Laser material processing: from fundamental interactions to innovative applications

Resume : Throughout the last decade Bessel-Gauss beams have gained lots of interest in laser micro-fabrication. The distinct property of elongated focal zone has used in many applications where various tasks are achieved with high efficiency, quality and speed. Such applications where high width/depth aspect ratio is required range from micro-channel fabrication to efficient stealth dicing of various transparent materials. Despite its broad applicability, high quality micro-fabrication is critically dependable on the quality of the beam, or the optics with which they are generated. Bessel-Gauss beams are formed in the lab commonly using an axicon. The quality of glass axicons, especially the low sharpness of the tip, and irregularities of its surface and volume greatly reduces the quality of the generated beam – axial intensity modulations usually emerge. The fabrication of refractive axicons with great precision requires high precision machining and is a challenge to fabricate, therefore alternative methods of Bessel beam generation are emerging to substitute glass axicons and consequently to increase the quality of the beam inside a focal region. This could reduce the complexity of the setup eliminating the need of spectral filtering. Common alternatives are diffractive optical elements (DOEs) based on active liquid crystals or metasurfaces. This allows to have a high level of freedom in beam shaping, however, the manufacturing is sometimes complex and usually not feasible in the lab. Nevertheless, this is not the case for geometric phase optical elements (GPOEs) also referred as Pancharatnam-Berry phase elements. These elements are based on the anisotropy of nanogratings induced in fused silica. The control of orientation and retardance of nanogratings enables to create various phase retarders that can work as any beam shaping optical element. In this work we present geometric phase optical elements (manufactured by Workshop of Photonics) inducing cone shaped phase profile, and show high quality generated Bessel beam. We also show, that it is possible to spatially displace half of the cone and form superpositions of high quality Bessel beams. We apply these beams systematically for thin glass cutting with high peak power ultrashort pulsed laser. Numerical, analytical calculations of beam shapes and experiment work are carried out to demonstrate generated Bessel type beams invariant propagation and show the performance of them in laser micro-fabrication applications.

Resume : Laser beam shaping finds more and more applications in the fields of free-space and quantum communications, optical trapping, nano-fabrication and others. Moreover, the evolving technologies of a nano-fabrication or spatial light modulators lets us to produce not only smaller, but also more accurate and having other superior properties elements for beam shaping. Advances to the process of beam shaping is enabled not only by theoretical and experimental studies on various beam shaping elements and light interactions with matter, but also by introduction of new types of laser beams with novel properties. One of the most intriguing beams in photonics are so-called non-diffracting beams. Non-diffracting beams are robust in variety of applications due to their linear focus and might have such vortical properties like orbital angular momentum of light. The beam can heal itself after being perturbed in phase or amplitude by an obstacle. These beams can also carry a phase singularity either in their phase (optical vortex) or in polarization. During the interaction with particles the angular momentum can be transferred to an object, so it starts to spin and/or is optically trapped by forces and torques of the impinging beam. In this work we introduce a novel polarization state to cylindrically shaped Bessel vortex beams – spherical polarization. The resulting beam differs from the well-known Bessel-Gauss beams in a way that spherical polarization state modifies intensity profile of the cylindrical beam. Usually vector Bessel-Gaussian beams are either linearly or radially and azimuthally polarized and the polarization state does not interact significantly with the cylindrical nature of the nondiffracting beam. Here, the Bessel-like beams with a Gaussian envelope are either spherically - radially or meridionally – azimuthally polarized. By controlling topological charges of the beam and Bessel cone angle, we report on novel types of intensity distributions that are shaped like an optical ‘bottle’ or like a double needle. We study interaction of these optical beams with spherical particles and report on possible applications.

Resume : Humankind has always been fascinated by light. But, besides just mesmerising us, light can also be a powerful tool for manipulating matter and its characteristics. Light is no longer limited to just a diagnostic for probing materials’ characteristics, but has also become an engine for manipulating materials’ properties. This presentation is about using light in order to process or fabricate thin films and manipulate their characteristics. As an alternative to conventional thermal annealing, laser processing enables the use of temperature sensitive substrates without any loss in the effectiveness of a high temperature treatment. Laser processing is amenable to the demands of R2R, providing a highly localised and ultra rapid thermal treatment, which targets the material of choice only and has minimal influence onto the surrounding materials. The 10 parameters that affect the outcome of laser processing will be presented in detail, offering a description of how they may affect the outcome of the processing and transform the characteristics of oxide thin film materials. Successful application of laser processing on all three types of materials required in transistors (namely conductors, semiconductors and dielectrics) will be presented. These examples demonstrate cases of effective dopant activation, control of defect and crystal structure, as well as highly localised heating for the photo-chemical conversion of sol-gel precursors to oxide thin films of high quality for transistors.

Resume : We develop ZnO/p-Si photodetectors by ALD deposition of ZnO thin films on laser-microstructured Si, with high sensitivity and broadband operation (UV-Vis-NIR), due to increased specific surface area of the heterojunction and increased light absorption. ZnO is very promising for optoelectronic applications due to its wide direct bandgap (3.37 eV) and large exciton binding energy (60 meV). Despite these advantages, the difficulty in introducing reproducibly high-quality p-type impurities in ZnO remains the main drawback in optoelectronic applications based on ZnO p-n homojunctions. Therefore, ZnO optoelectronic devices rely on heterojunctions with other p-type semiconductors, such as p-Si. Microstructured Si substrates were fabricated by nanosecond laser processing in SF6 gas. A pulsed Q-switched Nd:YAG laser system was used with 532 nm wavelength, 5 ns pulse duration, and 10 Hz repetition rate. Thin ΖnO films (200 nm) were deposited on the micro-Si substrates by ALD, forming a conformal ZnO/p-Si heterojunction. Bottom Al electrodes were deposited on the back surface of Si, followed by thermal annealing (300oC, 40 min) in pure N2 ambient, and top finger Al electrodes were deposited on ZnO. The microstructured ZnO/p-Si device is characterized by SEM microscopy. EDS spectroscopy shows conformal coating of the micro-Si substrate with ZnO by ALD. XRD analysis of ZnO films deposited under identical conditions show they are textured polycrystalline films, with a preferential orientation of the crystal grains with the (100) crystallographic planes parallel to the surface. Photoluminescence (PL) spectra of ZnO on flat-Si and micro-Si substrates show that microstructuring of the substrate does not affect the main emission properties of ZnO. However, ZnO on micro-Si shows a decreased PL intensity compared to ZnO on flat Si, since part of the emitted light is “trapped” in the microstructured surface, as a result of multiple reflections, which correlates well with the increased absorption of micro-Si. We compare the responsivity (photocurrent per incident light power) of ZnO/flat-Si and ZnO/micro-Si photodetectors. The responsivity of ZnO/micro-Si is higher than that of ZnO/flat-Si for all wavelengths within the investigated spectral range. Therefore, the ZnO/micro-Si device exhibits enhanced responsivity across the entire UV-Vis-NIR spectrum. The responsivity enhancement is more pronounced for the NIR wavelengths where the ZnO/flat-Si device is not responsive. On the other hand, laser-structured Si in SF6 (black Si) absorbs near-infrared photons below the Si optical bandgap due to sulfur states introduced into the bandgap of Si. I-V measurements under 1550-nm illumination also show a responsive ZnO/micro-Si photodetector. The overall enhanced responsivity of the ZnO/micro-Si device is attributed to the increased specific surface area of the heterojunction and to increased light absorption, due to multiple reflections of incident light.

Resume : The addition of a new side-injection ion source combining µm-scale laser desorption with laser ionization to an existing hybrid ion-trap time-of-flight mass spectrometer (Fasmatech) leads to unique chemical imaging capabilities. The new ion source is fitted with a precision (piezoelectric) XYZ positioning stage. The sample holder can be cooled down to -40°C using liquid nitrogen. Two microscope objectives (one refractive and one reflective) enable simultaneous µm-scale laser desorption, fluorescence and transmission/reflection optical microscopy studies. The sample is irradiated at normal incidence by a desorption laser beam (Nd:YAG, 532/266 nm, 4 ns, 10 Hz), focused on the sample surface by a Cassegrain objective. Laser shots can be rastered over the sample surface using the sample positioning platform, allowing the acquisition of chemical maps with complete mass spectra recorded at each pixel. A second laser (Nd:YAG, 266 nm, 4 ns, 10 Hz) intercepts and ionizes the expanding desorption plume in orthogonal direction. The ions generated are then guided to a segmented RF octapole trap and analyzed by an orthogonal time-of-flight mass analyzer that can reach 35k mass-resolving power. The decrease in desorption laser spot size down to 7 µm along with the automated sample positioning has empowered us to map chemically the analyzed sample surface. The chemical image obtained can be compared with the real-time optical image taken by either transmission or reflection microscope. The analytical applications of this µ-L2MS (two-step laser mass spectrometry) technique include organic and inorganic advanced materials as well as geological, biological and environmental samples.

Resume : In LIBS, a laser pulse ignites a plasma at the surface of a sample, which is then spectroscopically analysed. In LIBS-Stratigraphy, this procedure is repeated, subsequent pulses ablate layer after layer, penetrating the sample. One of the challenges in LIBS-Stratigraphy has been the recovery of the crater depth. A common approach is to assume a material dependent average ablation rate. However, due to complex light-matter, light-plasma interaction, fluctuations among the laser pulses and incubation effects, the ablation rate varies wildly throughout one LIBS experiment and it has been shown that this measure is neither linear, nor does it solely depend on the material composition. Optical Coherence Tomography (OCT) is a well established imaging technique wherein a low-coherence light source is used in an interferometer to gain depth information of a sample. Typically, a narrow beam is scanned over the surface capturing three dimensional features of a sample, which have been used to analyse LIBS craters *ex-situ*. We present an approach to measure the crater depth and shape *in-situ* and online without any moving parts, yielding a dynamic history of the crater formation. This gives us access to interesting parameters, such as the true ablation rate and thus a mapping of the LIBS spectra to their true depth. Possible use cases range from fundamentals such as the study of incubation effects to applications such as the recovery of mass density using only optical tools.

Resume : The integration of metallic plasmonic nanoantennas with quantum emitters (QE) fundamentally alters their optical nonlinearities. Such hybrid nanosystems promise a plethora of novel applications, from ultrafast all-optical switching to random nanolasing and enhanced harmonic generation. Here, we explore a new platform for implementing these functionalities: percolated individual Au nano-sponges, fabricated by solid-state dewetting of silver/gold bilayers. We show that such sponges support hot spots that are localized on a 10 nm scale with long plasmonic lifetimes and exceptionally high Purcell factors [1]. Their large field enhancements make them appealing as efficient photoemitters [2] and for plasmon-emitter coupling since different types of QE can be infiltrated into the nanopores without the need for lithography methods [3]. We study the dynamics of this plasmon-QE coupling by probing time-resolved interferometric nonlinear emission from individual porous gold nanosponges infiltrated with zinc oxide QE. We demonstrate boosting of second harmonic and uncover the quantum pathways nonlinear QE-plasmon coupling. Our results offer new opportunities for enhancing and coherently controlling optical nonlinearities in hybrid nanoantennas. [1] J. H. Zhong et al., Nano Lett. 18, 4957 (2018) [2] G. Hergert et al., Nature Light 6, e17075 (2017) [3] J. M. Yi et al., ACS Photon. 6, 2779 (2019) [4] J. H. Zhong et al., Nature Comm., in press (2020)

Resume : The understanding of the light coupling process on a surface irradiated by ultrafast laser is the most promising strategy to address a nanoscale control of surfaces topographies. Ultrafast optical scattering by the surface is governed by the local nano-roughness and the mutual response of the nanostructures through both radiative and non-radiative fields interaction. The roles of collective effects and inter-pulse feedback on the resulting surface topographies are examined in terms of both experimental and 3D numerical approaches to identify the nature of the intriguing self-regulation process. Laser-induced periodic surface structures were realized on Ti samples and photoemission electron microscopy (PEEM) with a spatial nm resolution was employed for imaging the ultrafast laser light distribution on the pre- structured surfaces. Periodical distributions of light were progressively observed with a frequency shift as the number of applied pulses increases. Concentrated hot-spot patterns were revealed to be superposed to this expected periodic absorption, with the demonstration that nanostructures periodicity reducing is driven by the concentration of the local-field enhancement centers. Self-organization of matter on ultrashort laser-excited surfaces is a complex multiscale phenomenon, implying dynamic coupling between incoming coherent light and evolving material, driven out-of-equilibrium. A new way towards efficient fabrication of surface periodic nanostructures will be presented with the evidence of direct sub-100 nm arrays of nanostructures. A. Abou Saleh et al., ACS photonics 6, 9, pp 2287-2294 (2019) X. Sedao et al., ACS photonics 5, pp. 1418 (2018) A. Rudenko et al., Nanophotonics 8, pp. 459 (2019) A. Abou Saleh et al. Nanoscale, pp. 6609-6616 (2020)

Resume : Wide-gap semiconductors, such as ZnO and GaN, are well known for exhibiting a LASER effect in UV [1], where their resonant frequencies are located. This LASER radiation is commonly interpreted in the context of the recombination of an electron-hole plasma [2]. However, the exact mechanism behind the amplification at room temperature is not yet clearly established, especially the precise wavelength at which amplification takes place was not predictable. In this work, we hypothesize that the mechanism that drives the sharp amplification on the redwing of the recombination spectrum might be the resonant Rayleigh scattering. Firstly, we present here an ab-initio calculation of the optical gain for these two materials, including renormalization of the gap and filling of the bands. This allows to find the carrier density at laser threshold and set the corresponding resonant frequency. Then, we compare the synthetic spectrum resulting from our computation to those obtained experimentally. We show that the experimental amplification fits with high accuracy the Lorentzian shape of the Rayleigh scattering spectrum. Moreover, the shrinkage of the band-gap explains the red-shifting of the LASER peaks, whereas the maxima of the optical gain are blue-shifted. Furthermore, we demonstrated that the FWHM of the LASER peaks, for GaN and ZnO, are given by the damping coefficient of the resonance of the Drude-Lorentz model. [1] H. Zhu et al, J. Phys. Appl. Phys. 50 (2017) 045107. [2] M.A.M. Versteegh et al, Phys. Rev. Lett. 108 (2012) 157402-1.

Resume : Raman and Tip-Enhanced Raman Spectroscopies (TERS) are very powerful techniques to investigate the electronic and molecular structure of nanoscale materials. First, we report on photochemical and photophysical properties produced by Surface Plasmon Resonance (SPR) on metallic nanograins by means of high resolution (TERS). We describe the local variation of plasmon-induced Raman enhancement on the surface of nanostructure that also affects the photochemistry near the functionalized tip apex. Our TERS maps with 10 nm spatial resolution show Raman modes of hot electron reduction of 4-nitrothiophenol molecules on the tip and indicate at least partial photochemical dimerization. An apparent photo-induced reversibility of this dimerization can be conservatively explained by a local topography feature that we simulate in a finite element environment. Second, we have studied the surprising pressure effects on luminescence spectra of a series of molecular chromium(III) complexes and compare with the well-established properties of doped solids. Luminescence and Raman spectra and their variation with external pressure are presented. The pressure-induced red shift of 11 cm 1/kbar in [Cr(bpy)3]3 and similar molecular compounds is higher by more than an order of magnitude than for chromium(III) doped oxides, widely applied as pressure sensors.

Resume : Angular and time-resolved measurements were performed by implementing the Langmuir probe technique for the investigations of transient plasmas generated by ns-laser ablation of Ag in various background gases. The aim of this work was to implement a relatively simple technique and to understand how we can control the ionic energy distribution during the deposition process. The experiments were performed on laser plasmas generated on Ag targets at a constant irradiation condition (λ = 266 nm, ν =10 Hz and E = 80 mJ) in various expansion regimes (p = 10-6 – 10 Pa). The Langmuir probe measurements were performed for various gasses (O2, N2 and Ar) in order to understand the effect of background gas nature on the ionic energy distribution. The electrical investigations were mainly focused on recording the saturation ionic and electronic currents at various angles (in a 45 deg range) with respect to the main expansion axis at 4 cm from the target in the vicinity of the substrate holder. For each investigated pressure a time-resolved analysis was performed on the main expansion axis which allowed the determination of a wide series of plasma parameters and their spatial evolution. The novelty of the study comes from recording also the floating potential in all conditions. This approach allowed us to showcase a multiple structuring of the Ag laser produced plasmas and to reconstruct the ions energy distribution. The structuring is seen in the ionic part of the collected current and confirmed by the fast electrons distribution which matched the ionic one. Each structure characterizes an ionization state of the Ag ions, results confirmed by performing optical emission spectroscopy along the main expansion axis and discussed in the framework of multiple double layer formation during plasma expansion.

Resume : Pulsed laser irradiation of metals can result in hierarchically structured surfaces comprising meso-, micro- and nano-structures that determine surface properties such as reflectivity, wettability, or friction. For vacuum components in particle accelerators, the aim of laser-induced surface modifications is the reduction of the escape probability of secondary electrons and changes of the optical properties. While laser-induced secondary electron yield (SEY) reduction of laser-textured copper has mainly been reported for 532 nm ps-laser processing, this study explores the applicability of other wavelengths by comparing treatments in air with 355, 532 and 1064 nm light of a laser with 12 ps pulse duration, with the aim to determine optimum processing parameters for the fabrication of a large-area, homogeneously nanostructured oxygen-free copper surfaces with reduced SEY. The influence of the most relevant treatment parameters (laser power, scanning line distance and scanning speed) on the interaction and ablation depths, the degree of surface oxidation and the change in surface topography is analysed and the SEY is measured likewise. Similar surface structures and material characteristics are observed for all investigated laser wavelengths. The SEY maximum can be reduced from above 2 down to 0.7. These low SEY values are achieved for a wide range of applied power density. Independent of utilized wavelength, a comparable dependence of ablation depth and SEY on the accumulated spatial energy density is found, indicating that the surface processes are nonlinear and that optical reflectivity is not a valid parameter to predict processing efficiency in the picosecond pulse regime. Consequently, processing with 1064 nm light sources is technologically promising for the intended application of SEY reduction due to the higher processing efficiency, the wider processing window and the stability of the laser beam.

Resume : Laser material processing is highly versatile and has a wide range of applications. The pulsed laser radiation can be used for the formation of temperature gradient field leading to the redistribution of atoms and formation of different structures, for example, nanocones [1], graded bandgap structures, and heterostructures [1,2], etc. In this study, we applied nanosecond laser radiation for GeSn epitaxial solid solutions grown by the MBE method with the aim to exceed the equilibrium solubility of Sn atoms in Ge host material. It will provide the extension of spectral sensitivity of GeSn photodiode in the IR spectral region. The main problem for the formation of uniform GeSn relaxed layers by MBE: the large lattice mismatch of 14.7% (19.5%) between α-Sn and Ge (Si) [3]; less than 1% of equilibrium solid solubility of Sn in Ge [4]; the extremely high surface segregation of tin at higher Sn content [5]. The limited solubility of Sn in Ge and the large lattice mismatch between GeSn and Si leads to compositional fluctuations, Sn segregation, and significant roughening [5]. The Ge0.95Sn0.05/Si structures were irradiated by pulsed Nd:YAG laser: wavelength 1064 nm, pulse duration 6 ns, the repetition rate of 10 Hz, and a beam diameter of 0.5 mm. Four different intensities were used. Scanning of the laser beam was performed normally to the GeSn surface with a speed of 0.2 mm/s and hatch of 0.1 mm. The irradiation of the samples was carried out at room temperature in the Ar chamber. Photodiodes were formed on non-irradiated and Nd:YAG laser irradiated layers and characterized by using femtosecond laser pulses with the wavelength in 2.0-2.6 µm range. The laser-irradiated diode was found more sensitive in the long-wavelength due to laser-induced Sn atoms redistribution providing formation of graded bandgap structure. Analysis of SEM, TEM, AFM, EDS, XRD results provided evident microstructural and compositional changes as Sn drift to the surface and its more homogeneous lateral redistribution. XPS analysis demonstrated obvious tin atomic concentration dependence on used laser intensity. Acknowledgments The work was supported as part of the Program on Mutual Funds for Scientific Cooperation of Lithuania and Latvia with Taiwan, Project No. S-LLT-18-1. Pavels Pavels Onufrijevs has been supported by the European Regional Development Fund within the Activity 1.1.1.2 “Post-doctoral Research Aid” of the Specific Aid Objective 1.1.1 “To increase the research and innovative capacity of scientific institutions of Latvia and the ability to attract external financing, investing in human resources and infrastructure” of the Operational Programme “Growth and Employment” (No. 1.1.1.2/VIAA/3/19/409). References [1] A. Medvid et al., Nanoscale Res. Lett. 8, pp.1–8, (2013) [2] P. Onufrijevs, et al., Opt. Laser Technol. Vol. 128 pp. 106200 (2020). [3] Z. Liu et al., Sci. Rep., vol. 6, no. June, pp. 1–9, (2016). [4] E. Kasper, J. Mater. Res., vol. 31, no. 23, pp. 3639–3648, (2016). [5] L. Kormoš et al., Surf. Interface Anal., vol. 49, no. 4, pp. 297–302, (2017).

Resume : Laser thermal annealing (LA) is integrated, as micro- and nano- electronics processing step, when strongly confined heating is needed in the semiconductor device manufacturing flows. One of the main challenges for the application of the process in future devices is to achieve an optimal process control. That is why a reliable simulation of the process is needed, and despite models of LA have been implemented in academic or commercial packages, a further evolution of the methods is necessary for the general application in complex structures with nm wide elements where the thermal transport could be dominated by phonon effects. Moreover, ultra-fast (explosive) phase transitions occurs during the irradiation of device elements and their modelling is a challenging objective for the LA simulators’ development. In this context we integrate phonon transport corrections and modeling of explosive crystallization to our existing simulation tool, LIAB (LASSE Innovation Application Booster) that will help us to reproduce experimental data and predict behavior of semiconductor structures upon laser annealing. About the phonon corrections we simulated thermal transport induced by conventional and laser annealing in various structures comparing the results in which standard conditions and corrections were applied, noticing that there is a size dependent discrepancy between standard and corrected solutions. Regarding explosive crystallization we successfully simulated this challenging behavior including secondary melting during the process. The code we developed uses the FEniCS computing platform for solving continuum fields evolution and Gmsh as 3D finite element mesh generator.

Resume : Metal or semiconductor nanoparticles can be generated by UV light directly in solid polymer matrices where the appropriate precursor is dissolved. At least Au [1] and CdS [2] particle generation in poly(methyl metacrylate) matrices has been reported so far. In this work, we describe possible physical mechanisms that can be in charge for the nucleation and particle growth in polymers, taking into account their macromolecular nature [3]. Theoretical models describing the homogeneous and heterogeneous nucleation regimes are proposed and compared. The authors are grateful to the Russian Science Foundation (Project No. 18-79-10262) for financial support. 1. N. Bityurin, A. Alexandrov, A. Afanasiev, N. Agareva, A. Pikulin, N. Sapogova, L. Soustov, E. Salomatina, E. Gorshkova, N. Tsverova, and L. Smirnova, "Photoinduced nanocomposites—creation, modification, linear and nonlinear optical properties," Appl. Phys. A 112, 135–138 (2013). 2. A. A. Smirnov, V. Elagin, A. Afanasiev, A. Pikulin, and N. Bityurin, "Luminescent patterns recorded by laser irradiation of a PMMA matrix with a soluble CdS precursor," Opt. Mater. Express 10, 2114 (2020). 3. A. Pikulin and N. Bityurin, "Homogeneous Model for the Nanoparticle Growth in Polymer Matrices," J. Phys. Chem. C 124, 16136–16142 (2020).

Resume : Doping allows us to modify semiconductor materials for desired electrical, optical and magnetic properties. Ion implantation followed by annealing is a well-established method to dope Si and Ge. This approach has been maturely integrated with the IC industry production line. However, being applied to hyperdoping where the dopant concentration is much beyond the solid solubility, the annealing duration has to be shortened to millisecond or even nanosecond. Pulsed laser provides a unique processing method to recrystallize ion-implanted semiconductors. The molten layers undergo a fast cooling and recrystallize epitaxially on the beneath semiconductors with the time duration less than micro-second. In this process, the foreign impurities have limited diffusion time and can be effectively trapped into the lattice sites, leading to doping well beyond solid solubilities. In this talk, we propose that ion implantation combined with pulsed laser melting in nanosecond can be a versatile approach to fabricate hyperdoped semiconductors. The examples include magnetic semiconductors [1-5], Ge1-xSnx [6], and chalcogen doped Si [7-10]. [1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014). [2] S. Zhou, J. Phys. D: Appl. Phys. 48, 263001(2015). [3] S. Prucnal, et al., Phys. Rev. B 92, 222407 (2015). [4] Y. Yuan, et al., ACS Appl. Mater. Interfaces, 8, 3912 (2016). [5] Y. Yuan, et al., Phys. Rev. Mater. 1, 054401 (2017). [6] K. Gao, et al., Appl. Phys. Lett.,105, 042107 (2014). [7] S. Zhou, et al., Sci. Reports 5, 8329(2015). [8] M. Wang, et al., Phys. Rev. Applied. 10, 024054 (2018). [9] M. Wang, et al., Phys. Rev. Applied. 11, 054039 (2019). [10] M. Wang, et al., Adv. Optical Mater. 2001546 (2021).

Resume : This study addresses the experimental and theoretical optimisation of an additive lunar soil simulant laser sintering process done at the ICube laboratory, Illkirch, France. Combination of In-situ Resource Utilization (ISRU) and on-site Additive Manufacturing (AM) is one of the ?outer space applied technologies? candidates in coming future Moon settlements or potentially other celestial bodies for long duration human exploration. AM using lunar soil as a main resource which will help to reduce the amount of equipment needed to be carried along, thus greatly lowering the cost of the mission. Thanks to this technology, human shelters, or smaller parts, such as tools, fastening and support parts for a wide range of applications, can be manufactured on site. A diversity of synthetic lunar regoliths were tested as simulants in our experiments (JSC-2A, LHS1 and LMS1). A powder bed on X/Y translation stages was heated by a continuous 100W fibre laser emitting at 1090 nm. The numerical multiphysic model developed on COMSOL for this study is based on the composition, density, granulometry, optical, and thermal properties such as conductivity, heat capacity and latent heat of fusion of the aforementioned lunar regolith simulants. The simulations of the light/matter interactions were used to help assess the variability of the processing parameters. Experimental results obtained showed that the various simulants require different parameters for efficient laser melting/sintering: energy intensities, scan speeds, and hatching space. The experimental results are in good agreement with the output from the Multiphysics models: the theoretical heat affected zone is in accordance with the optical measurement of the various melted/sintered samples.

Resume : Niobium metal is the pure element with the highest superconducting critical temperature (Tc= 9.2 K), which is present in many applications. Particularly, in superconducting radio frequency (SRF) cavities of particle accelerators, the control of the surface characteristics of pure Nb is crucial, as the presence of defects may generate magnetic flux pinning that can increase by more than two orders of magnitude the surface critical current, ic. Several procedures such as chemical- or electro-polishing have been used aiming at cleaning surface contamination and decreasing its roughness. Sub-nanosecond lasers can be applied to generate a broad range of micro and nanostructures (e.g. Laser-Induced Periodic Surface Structures, LIPSS) that strongly modify the materials properties - as wettability, color, oxidation resistance or antibacterial behavior. In this work, we analyze a variety of surface structures generated on pure Nb sheets with different laser systems (UV, Vis and n-IR, fs and ps) by exploring a range of processing parameters. These include pulse overlap, irradiance or the effective number of pulses, under different atmospheres (air, N2, Ar, vacuum). The effects on Tc, critical currents and critical fields (Bc1, Bc2 and Bc3) have been obtained from magnetization, ac susceptibility and heat capacity measurements, revealing their dependence with the different surface nanostructures and the chemical changes generated with these laser treatments.

Resume : Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescent in expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study we report the use of Sudan Black B as both a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080TM for the development of a non-fluorescent composite. We use this material for the 3D printing of micro-optical elements, and meso-scale scaffolds for Mesenchymal Stem Cell cultures. Our results show the hybrid, made photosensitive with Sudan Black B, can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

Resume : The formation of laser induced periodic surface structures (LIPSS) on organic surfaces has been one of the key research lines in the laser processing of polymer materials for over the past decade. Besides the investigation about the mechanisms of formation, these nanostructures have shown their potential use in a broad range of applications. However, in most of the so-far published works, LIPSS formation is usually carried out in ambient conditions. To provide further insight into the growth mechanisms of LIPSS and their impact on the physical properties of nanostructured surfaces, we present a work dealing with LIPSS formation under controlled environments. Here, we show the possibility of preparing nanostructured surfaces of poly(ethylene terephalate) (PET) under vacuum, water, alcohols, and oils. We noticed that depending on the surrounding medium, nanostructures with different shapes were formed, not always following the geometrical characteristics of ?usual? LIPSS. We have also quantified the physicochemical properties of the irradiated structures by combining macroscopic and nanometric techniques. In the latter case, we made emphasis on the quantification of local properties using Atomic Force Microscopy (AFM). In particular, nanomechanical AFM measurements showed that laser structuring lead to important changes on the mechanical characteristics of the surfaces, reflecting on the Young?s modulus, stiffness, and adhesion force.

Resume : In this work, we present some results and analysis concerning the processing of semiconducting CdSe nanoparticles obtained by laser ablation of diluted CdSe powder in acetone. An Nd-YAG pulsed laser was used for ablation, tuned at the first and second harmonic, λ=1064 and 532 nm, 50 Hz frequency repetition for 30 minutes. The experiment was performed at different power intensities. An important difference in the size of the samples synthesized at 1064 nm and 532 nm is observed, being 12 nm for the samples processed with the infrared line and less than 5 nm for those processed with the green line. The emission and absorption of the samples run from 1.8 to almost 2.4eV for the smallest particles; in addition to this, by Raman spectroscopy, it is possible to differentiate between surface mode phonon and longitudinal optic phonon in samples synthesized at 532nm. A complete characterization by UV-Vis Absorption, Photoluminescence, Raman, Energy Dispersive Spectroscopy, Transmission Electron Microscopy, and X-Ray Diffraction is presented and analyzed

Resume : Fs-Laser Induced Periodic Surface Structures (LIPSS) on thin films have been found to be strongly affected by the substrate where the film is deposited. We propose that this behavior is caused by surface electromagnetic field enhancement associated to the generation of surface plasmon polaritons (SPP) in the interface between the thin film and the substrate, which will behave as a metal because of the laser excitation. We simulated, by means of COMSOL’s Wave Optics module (Finite Element Methods), the field that would result from the plane wave irradiation of a polymeric thin film on different substrates. We found that the intensity of the generated SPPs increases with the substrate mean roughness (Ra). However, they fail to form when the Ra increases above a certain threshold. This could mean that there is a limit to the substrate roughness that allows LIPSS generation on the surface of the thin film. Moreover, the influence of the roughness parameters on the SPP period and penetration length was studied. Although we did not observe a strong correlation between them, the higher the Ra the greater the standard deviation values for the period and penetration length. This can be interpreted as a loss of the uniformity of these parameters across the surface which is consistent with the observed absence of LIPSS for rough surfaces. Regarding the thickness of the thin film, we compared the period of the SPPs of our simulations with those given by the theory of SPP in thin films finding that the simulated period was always smaller than the theoretical one. We think that this is a consequence of the modification of the dispersion relation of SPPs when they propagate on a rough surface.

Resume : In stratigraphic LIBS analysis, the objective is to follow the change of elemental composition along the incident laser beam. However, due to complex light-matter, light-plasma interaction, fluctuations among the laser pulses and incubation effects, the ablation rate typically varies wildly throughout one LIBS experiment. In this work we present a proof of concept to use a coaxially mounted non-scanning single-spot (NoSc-SiSp) optical coherence tomography (OCT) for in-situ absolute depth measurements between the LIBS laser pulses. Unlike standard OCT, we do not use a very narrow, needle-like OCT-beam to scan over the surface of a sample. Instead, a wide OCT-beam is used, losing all the lateral information. This enables us to use OCT coaxially with the LIBS ablation path, passing the same optics and obtain information about the surface and the LIBS crater at the same time.

Resume : The intrinsic nanoscale point defects generating in the crystal lattice of ZnSe during the crystal growth and doping processes strongly determine the functional properties of the material as well as dopants (Fe, Cr) solubility. Nonstoichiometry and IR luminescence spectra of ZnS:Cr:Fe ZnSe:Cr:Fe powdered preparations and CVD-grown ZnSe:Fe:Cr crystals treated by high-temperature gas-static pressing (HIP) were changing depending on Fe and Cr doping level and preparation conditions. Whereas the nominally pure CVD-ZnSe crystals had excess of Zn over stoichiometric composition, all the Fe-doped ZnSe crystals had an excess of chalcogen. This correlates with the results of the Zn-Se-Fe phase diagram analysis. Isothermal sections of T-x-y-z diagrams of ternary Zn-S-Fe, Zn-S-Cr and quarternary Zn-S-Fe-Cr, Zn-Se-Fe-Cr were reconstructed and experimentally confirmed by X-ray diffraction and Energy Dispersive X-ray spectroscopy (EDS) in the temperature range of 873 K - 1088 K. The homogeneity limits for ZnS:Cr:Fe and ZnSe:Cr:Fe phases have been determined. As a result of the control the intrinsic point defects Cr- and Fe-dopant levels we achieved the large quantities of differential efficiency of the produced ZnSe:Cr2 :Fe2 lasers. The research was financially supported by the Ministry of Science and High Education of the Russian Federation by the project FSSM-2020-0005

Resume : The machining of technical glass with beam technologies enables novel fabrication processes for innovative optical elements with free form surfaces but require technologies for high-precision, low roughness machining. Reactive plasma etching of N-BK7 is challenging due to the complex composition of glass and feature therefore potential limits related to forming of a residues layer. The presentation demonstrates a sequential plasma etching and laser cleaning process for N-BK7 glass machining. First the glass is etched with a fluorine gas containing reactive plasma jet (RPJ) resulting in an etched surface containing also residues that change the surface composition. After RPJ etching the residues are removed by pulsed UV laser irradiation without ablation of the glass. RPJ etching and laser ablation are applied repeatedly enabling a prolonged, stabile etching process that is required for industrial machining processes. First results of the combination process of RPJ etching and laser ablation are shown and discussed. Thus, RPJ etching and laser ablation (RPJE-LA) of N-BK7 are studied separately showing the limitations. Thereafter, important process characteristics RPJE-LA approach such as etching rates, surface morphologies and surface roughness are given. Further, selected results of the surface composition alterations are given. The mechanism RPJE-LA are discussed in relation to the characteristics both process steps and the experimental finding of the RPJE-LA.

Resume : (Ba, Sr)TiO3 (BST) ferroelectric solid solutions with Curie point close to room temperature have been extensively investigated over the last 30 years for their integration in microwave (MW) tunable devices. Recently, several terahertz applications based on BST thin films have been reported. In this work, we present and discuss on the THz and MW properties of the BST thick films grown on MgO(001) and Al2O3(0001) substrates by using pulsed laser deposition. As a result of a parametric study, single-phase samples with thicknesses between 2 and 5 µm are achieved. THz time-domain spectroscopy measurements in transmission are carried out successively on substrates before and after the BST film deposition. In order to extract the dielectric properties of the films from the THz data, the substrate is considered as an overmoded dielectric resonator, characterized by a regular series of resonance peaks in the THz transmission spectrum, loaded by the BST thin film. In this system, the complex permittivity of the film sample is obtained by the analysis of the shift and attenuation of the peaks induced by the sample, in a close analogy to dielectric measurements by means of Fabry-Perot resonators. The complex permittivity in MW domain of the obtained films are accurately measured at 12.5 GHz using a resonant cavity method. The tunability of the ferroelectric layers are determined by integrating them in planar inter-digitated capacitors (IDC) fabricated using standard microfabrication technologies. The MW characterization of the IDCs is performed in reflection configuration under various applied electrical fields. A 40 % tunability of the permittivity under an applied field of 100 kV/cm is achieved at 30 GHz for structures with optimized topologies. Acknowledgments: This work was supported by a grant of Ministry of Research and Innovation, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2016-1711, within PNCDI III.

Resume : Nowadays, photochromic systems are the subject of more industry-funded research in the field of high-tech applications that have the potential to become the most important commercialization point for photochromic dye. Our interest is in smart systems, sensors, printed or stamped elements due to their potential applications in these sectors. Here, we report on the fabrication of a photoluminescent coatings using Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. An organic dye with a spiropyran structure was prepared to be used as target in three different forms: i) as prepared, ii) microencapsulated in a poli oximetilen melamine resin matrix, iii) embedded in a layered double hydroxide matrix. Photochromic dyes like spiropyran materials synthesized via laser processing have not yet been reported. The spiropyran dye and spiropyran-based materials were transferred by UV laser (266 nm) on different types of substrates. In the present work, we studied the optical, morphological and the photochromic properties of the organic dyes thin films obtained by MAPLE, emphasizing the protective matrix function. Different techniques, as AFM, XRD, FT-IR, DRIFTS, DR-UV-Vis and Raman spectroscopic measurements have been used for the morphologic and structural characterization of the organic dyes films. A photochromic study was performed by measuring the photoluminescence (PL) emission spectra and fluorescence microscopy images of the as deposited spiropyran dye-based films.

Resume : We show the performance of fully automated 1064 nm picosecond LIBS on samples generated by Laser Metal Deposition (LMD) as well as Cold Metal Transfer (CMT) welding. The first method uses micrometer-sized metal powders of various composition mixed in an inert gas jet and coaxially directed onto the meltpool generated by a CW-laser on the workpiece’s surface. This way, chemically graded 3-dimensional structures can be generated based on complex physicochemical models, resulting in functionally graded workpieces with laterally varying physical properties [1]. CMT has become a standard-technique to join light metal parts of different composition, shape and thickness in the automotive and aerospace industry. In particular the latter one requires high-standard quality and process control in real time. In both cases LIBS can be used as a parametrisation method for new buildup processes as well as a real-time online quality control tool with potential to by fed back in the LMD-process via closed-loop coupling. We present various lateral and in-depth chemical mapping analyses of multi-layer and multi-material parts, validated via metallographic cross-sections and scanning electron microscopy/x-ray spectroscopy. [1] https://doi.org/10.1016/j.addma.2018.06.023 [2] https://doi.org/10.1364/OE.27.004612 [3] https://doi.org/10.1016/j.addma.2018.10.043

Resume : Molybdenum oxides are versatile semiconductors whose optical and electronic properties depend strongly on their stoichiometry. In particular MoO3 is transparent and shows a wide bandgap (>3 eV) and a high dielectric constant k ~ 500. Additionally orthorhombic α-MoO_3 possesses the well-known layered crystal structure of MoO_3 which offers the possibility to create two dimensional (2D) morphologies. In this context, 2D MoO3 is an ideal material for electronic applications for high power electronics and short wavelength optoelectronics that materials with a wide band gap and high crystallinity in 2D limited thickness. In this contribution we show the successful preparation of thin films formed by 2D MoO3 crystals by a pulsed laser deposition based process that starts with the deposition of dense and continuous substoichimetric MoO_x films with thickness of few nm by PLD in vacuum from a MoO_3 target. Subsequently, the films are annealed in air up to 300ºC while following the evolution of their optical properties in-situ in the UV-VIS wavelength region by spectroscopic ellipsometry. When the temperature reaches 250ºC a clear change in the optical properties starts that is related to the films crystallization. Analysis of the optical properties shows how the initially absorbing films with a metallic-like behavior after the annealing become transparent in the NIR and VIS regions, and show a band gap >3 eV. Optical microscopy, AFM and electron microscopy show the formation of thin and large rectangular micron size α-MoO_3 single crystals; the structure and stoichiometry has been further confirmed by X-ray diffraction analysis, Raman and XPS spectroscopy. The full dielectric constant of α-MoO3 for the 2D crystals is reported for the first time and the implications for the optoelectronic applications will be discussed.// [1] I. A. de Castro, et al., Adv. Mater. 29, 1–31 (2017). [2] J-H Kim, et al., Nano Letters 19, 8868-8876 (2019)

Resume : Laser-based nanofabrication is a novel way of increasing the potential of micro/nanotechnologies and addressing new applications. The Double-Pulse Laser Induced Forward Transfer (DP-LIFT) technique appears to be a promising laser direct write approach to minimize the size of the printed structures and improve the flexibility of the process. In DP-LIFT, a long laser pulse is first applied to melt a solid thin film deposited on a transparent substrate, followed by an ultrashort laser pulse to initiate the transfer of the liquid material towards a receiver substrate. By controlling the irradiation conditions, ejections from nanodrops to liquid metal jets with controllable diameters, from few micrometers down to the nanometers scale can be obtained. In this study we investigated the transfer of copper. The jet dynamics is governed by various factors including the shape, diameter and temperature of the melted pool created with the long pulse. Numerical simulations of the temperature evolution of copper film gives an insight about the initial conditions for the interaction of the femtosecond pulse with the melted region. Time-resolved imaging of ejected copper yields direct evidence on the influence of the pool diameter and shape in the formation and break-up of thin nanojet and microjets. While the formation of microjet is due to the deformation of the film, as a basis of the conventional LIFT process, nanojet formation is attributed to shockwave effects combined with an appropriate pool shape.

Resume : A rapid, solvent-free laser based procedure, i.e. laser-induced forward transfer (LIFT) has been developed for the reproducible fabrication of sensitive sensors based on hybrid nanocomposites, i.e. single walled carbon nanotubes (SWCNTs) decorated with tin oxide nanoparticles (SnO2 NP). This nanocomposite overcomes challenges associated with solvent-assisted chemical functionalization and integration of these materials into devices. The gas response of the LIFT-ed SWCNT-SnO2 sensors has been evaluated at room temperature and an 2-times enhanced response to ammonia as compared to the SWCNT sensors is demonstrated. Spontaneous and full recovery of the hybrid nanocomposite signal after exposure to NH3 is achieved without any post treatment. The theoretical detection limit of the LIFT-ed SWCNT-SnO2 sensors at room temperature is calculated to be ~ 0.6 ppb. These results indicate that LIFT is an excellent technique which shows great promise towards advancing future developments in the field of chemical sensors. Keywords: sensor, ammonia detection, room temperature, LIFT, decorated carbon nanotubes, SWCNT, SnO2 Acknowledgement Financial support from UEFISCDI, though the 15PCCDI “Fabrication, calibration, and testing of advanced integrated sensor systems aiming at applications in societal security (TESTES)” project is gratefully acknowledged.

Resume : Current trends in designing medical and tissue engineering systems rely on incorporation of micro and nanotopographies for inducing a specific cellular response within the aimed application. As such, dedicated studies have recently focused on understanding the possible effects of high and low density packed micro topographies on behaviour of epithelial cells especially when considering their long-term viability and functionality. Herein we proposed to use stair like-designed topographies, with three different density degrees, all created in polydimethylsiloxane (PDMS), as active means to evaluate cell behavior. Our model cellular system was BEAS-2B, a reference line in the quality control of mesenchymal stem cells (MSCs). PDMS microtextured substrates of 4 µm square unit topography were created using a mould design featured by a KrF Excimer laser. Varying the spacing between mould features and their disposal in multiscale level led to irregular stairs/lines in low, medium and high densities respectively. Profilometry, scanning electron, atomic force microscopy, contact angle and surface energy measurements were performed for evaluating the topographical and interface characteristics, while density-induced cellular effects were evaluated by traditional cell-based assays. Our analysis showed that high density microstructures lead to uniform adhere profiles of cells while low-density microstructures lead to cellular clumps. Results confirm that step-like structures confine the cellular connection and limit their mobility while a rarer microstructure distribution allow cells agglomeration. Our analysis supports the hypothesis that epithelial organoid formation might be initiated by the restriction of cell spreading and migration by using user-designed and controlled micro-topographies on engineered surfaces. Keywords: polydimethylsiloxane (PDMS) replica, laser textured mould, BEAS cells, topography analysis, cellular behaviour. Acknowledgement This work was supported by the National Authority for Research and Innovation in the frame of the Nucleus Program and grants of the Romanian Ministry of Research and Innovation,UEFISCDI, project PCE 2021.

Resume : In recent years, transfer and patterning of graphene has been widely investigated, due to its interesting properties like extraordinary conductivity, flexibility and transparency. However, graphene based electronic devices are limited by the zero bandgap of single layer graphene. Alternatively, transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), have been considered a promising candidate for electronic device applications (i.e. field-effect transistors, optoelectronic devices). More specifically, MoS2 has a thickness dependent tunable bandgap, where the bandgap changes from direct (~1.8 eV) to indirect (~0.9 eV), from mono-layer to multi-layer, respectively. Here, we report on the use of Laser-Induced Forward Transfer (LIFT) technique for the reliable printing of a commercially available MoS2 ink (purchased from Sigma-Aldrich, solid content: 3.0-3.85%, viscosity: 4-11 mPa.s) in liquid and solid phase. In particular, LIFT process parameters have been examined (laser fluence, laser spot size, liquid phase on donor) to define the optimum process for reproducible transfer of MoS2 on silicon dioxide receiver substrates. Initial experiments, with 2 m/s scanning speed of the laser beam, resulted to printed drop patterns with diameters ranging from 50 to 100 μm. Next, a side-view imaging configuration is also employed by coupling a LIFT setup with a high-speed camera for the real-time visualization of the ejection process (liquid phase LIFT of MoS2). In this way, we illustrate and provide a detailed discussion of the dynamic behavior of MoS2 ink during laser driven drop ejection to understand the jetting evolution of the ink in order to predict the uniform and reproducible formation of drop patterns on top of source/drain electrodes of FET substrates. The captured videos are analyzed to determine ejection dynamics and morphological aspects, such as the volume of the printed pattern. The ejection velocity of the jet front was calculated around 12 m/s and volumes of the printed droplets had values ranging from 2.55 pL to 18.06 pL. Following the above experiments, the printed MoS2 was examined using RAMAN spectroscopy. Preliminary results showed the two characteristic Raman peaks (E12g and A1g) of MoS2. Finally, the reported process is applied for the printing of MoS2 on FET substrates in order to investigate the device performance.

Resume : Noble metal nanoparticles (NPs) have been attracting a lot of attention recently due to their size and shape dependant optical properties. Collective free electron oscillations driven by an external electromagnetic field in the confined space of an NP results in a so-called localized surface plasmon resonance (LSPR) featuring sharp extinction peaks in the optical spectra. Historically most metal NPs were synthesized chemically but with the advent of ultra-short pulse lasers, new pathways of synthesis and post-processing of monodisperse NPs have emerged. One of the main advantages of NPs synthesized by laser ablation in liquids (LAL) in contrast to chemical synthesis routes is that the resulting NPs can be made ligand-free. The exclusion of residual contamination is important for a myriad of bioapplications. The second important advantage is a simple and reproducible synthesis process that is scalable. Many laser parameters influence the yield and size distribution of the NPs because they are directly related to the complex temporal evolution of physical-chemical phenomena that take place during the laser ablation of a submerged metal target. To evaluate the structural and optical properties of NPs prepared by the LAL method their features should be explored in detail. In our study, we were focusing on the transient plasmonic properties of NPs synthesized from three plasmonic metal targets by the LAL technique. In this work, the fundamental harmonic (1030 nm) of a linearly polarized Yb:KGW femtosecond laser beam was utilized for ablation of pure Ag, Au, and Cu targets in ultrapure Type 1 water. The dependences of the resulting nanoparticles’ optical properties and size distributions on the laser processing conditions, namely pulse energy and pulse density, were investigated and the conditions ensuring the highest NP generation yield were highlighted. The dynamic plasmonic properties were explored by ultrafast transient absorption spectroscopy method exploiting Yb:KGW femtosecond laser and nonlinear parametric amplifier. The ultrafast LSPR relaxation dynamics in plasmonic NPs prepared by the LAL method were compared with the ones prepared by chemical synthesis. The TAS results indicate that the LSPR properties of LAL NPs are quite similar to NPs prepared by the wet chemical synthesis method suggesting that their qualities are also comparable. The preliminary results confirm that the physical-chemical synthesis of NPs could be a perspective tool preparation of high-quality plasmonic NPs for a range of applications where ligand-free materials are necessary.

Resume : In this work surface modifications of aluminium nitride (AlN) and silicon nitride (Si3N4) ceramics irradiated by nanosecond laser pulsed are studied. Laser processing is performed by Nd:YAG laser at four wavelengths – 266, 355, 532, and 1064 nm. It is found that laser treatment leads to variety of micro- and nanostructures on the surface of the material that are strongly dependent on the processing conditions. Experimental parameters, were the irradiation leads to formation of a conductive Al and respectively Si layers, are defined. The morphology, electric and optical properties of the modified zones are studied and discussed. Using a model based on the heat conduction equation the formation dynamics and the dependence of the layers thickness on the processing conditions is obtained. The formed structures can be used for UV plasmonics and optoelectronics.

Resume : Printed electronics have attracted significant research interest during the last decade owing to the advancement of printing technologies and the progress on the synthesis of novel materials. In particular, the combination of additive manufacturing processes with conductive inks of 2D materials i.e. graphene inks, has been widely employed in a broad spectrum of applications that span from touch sensors and displays to chemical sensors and Radio Frequency Identification. Here, we report our latest results on the site-specific and high-resolution printing of graphene inks onto conventional and flexible substrates using the Laser-Induced Forward Transfer (LIFT) technique. Using single laser pulses, LIFT enables the deposition of graphene inks with high accuracy, while preserving the functionality of this one-atom thick carbon material after transfer as supported by structural and morphological characterization. To study the jetting mechanism and establish a printability map for graphene ink printing we also employ high-speed imaging that reveals the dynamics of transfer and associates the printing outcome with the different jetting regimes that are mainly determined by the laser pulse energy for a given laser operating frequency. This work, we believe, provides further insights into the jetting mechanism of laser printed graphene inks for printed organic electronics applications.

Resume : Laser-induced periodic surface structures (LIPSS) are a universal phenomenon that is accompanying laser materials processing. These surface nanostructures pave a simple way for surface functionalization with numerous applications in optics, fluidics, tribology, medicine, etc. During the last decade remarkable experimental and theoretical improvements in understanding of their formation mechanisms were obtained - all pointing toward polarization-dependent energy deposition by absorption of optical radiation that is scattered at the surface roughness and interfering with the laser beam. This contribution reviews the current state-of-the-art on the role of electromagnetic scattering in the formation of LIPSS by ultrashort laser pulses. Special attention is drawn to recent finite-difference time-domain (FDTD) calculations that allow to visualize the radiation patterns formed in the vicinity of the sample surface and to the impact of a thin superficial laser-induced oxidation layer.

Resume : Pulsed laser ablation in liquid (PLAL) is an appealing technique to produce nano-carbon allotropes, from nanodiamonds to nanotubes [1]. Besides these most known forms of carbon, PLAL can efficiently synthesize polyynes, truly one-dimensional carbon systems, composed by a linear chain of alternated single and triple sp-hybridized bonds. They have attracted general attention for their predicted impressive mechanical and electronic properties [2]. By selectively tuning ablation parameters, such as fluence and liquid environments, we can obtain various chain lengths and terminating groups [3]. In this scenario, we have investigated ns-PLAL synthesis testing different organic solvents, especially alcohols. Ablation processes and parameters were studied to obtain the highest concentration of polyynes and the maximum synthesis yield. In particular, we have analyzed the fundamental role of the solvent and its two-fold function, i.e. to contribute as an alternative carbon source and to supply chain terminations. Absorption spectra and high-performance liquid chromatography (HPLC) analysis revealed the presence of H-capped long polyynes up to HC22H. Polyynes with other terminating molecules have been observed, namely methyl- and cyano-polyynes, till HC18CH3 and HC12CN, respectively. Size- and capped-selected polyynes have been separated through HPLC and further studied by surface-enhanced Raman spectroscopy (SERS), employing Ag nanoparticles colloids and films. We recognized the characteristic band of sp-carbon chains and we were able to distinguish between different end-groups, as predicted by DFT simulations. We proved the flexibility of PLAL to control the length and terminations of polyynes by properly optimizing the process parameters. These achievements are fundamental to functionalize polyynes for future optical and electronic applications. [1] D. Amans et al., Journal of Colloid and Interface Science, 2017, 489, 114–125. [2] C. S. Casari et al., Nanoscale, 2016, 8, 4414–4435. [3] S. Peggiani et al., Phys. Chem. Chem. Phys., 2020, 22, 26312–26321.

Resume : A new approach to describing the processes in ultrashort fs-ps laser ablation of metals is proposed within the framework of a non-equilibrium combined continuum-atomistic model. Ultrashort superpowerful laser action on condensed media is accompanied by the same powerful transfer of matter, which is characterized by high values of speed comparable to the speed of sound and high pressures. The description of such processes is carried out, as a rule, within the framework of various hydrodynamic models. At the same time, the atomistic approximation is used to describe the state of the lattice. Due to the great degree of nonequilibrium of the processes, a similar hydrodynamic transfer, but only for a short time, also occurs in the electronic component. It is known that at the metal - vacuum interface, there is a thin surface layer of spatially separated electric charges of the opposite sign - electric double layer (EDL), which arises as a result of the displacement of the electron gas outside the positively charged crystal lattice. EDL is generally electrically neutral. Non-equilibrium laser heating causes a rapid increase in the temperature and pressure of electrons. Excessive electron pressure leads to violation of the quasi-neutrality of the EDL and generates an additional force that exerts a tensile effect on the lattice ions. For EDL, the hydrodynamic representation is used, which is the most complete and general description of electronic processes in metals under non-equilibrium conditions of action. With a sufficient value of the force generated by the electric field, detachment of individual ions and their clusters occurs. The presented nonequilibrium combined model, taking into account the effects of the electric field, was used to simulate the fs-effect on the Al target. Mathematical modeling made it possible to find two ablation mechanisms, for which a bimodal velocity distribution of the removed substance was constructed. The first is that a nonthermal mechanism (Coulomb explosion) arises and develops in the course of a laser pulse. It is characterized by the removal of individual ions and ionic clusters propagating at a speed of ~ (8-15) km/s. The second mechanism appears after the end of the laser pulse in the unloading wave with negative pressure and corresponds to the thermal mechanism in experimental studies. It is the main mechanism for the removal of matter with characteristic velocities of tens - hundreds of m/s. The results obtained are qualitatively and quantitatively close to the experimental data. This work was supported by RSF, project 18-11-00318.

Resume : Ultrashort pulsed fs-ps-laser action on various materials leads to consideration of a number of important fundamental problems, which at high heating rates include the features of heterogeneous melting/solidification mechanisms and the associated ultimate overheating and undercooling of matter. The speed of movement of the solid/liquid interface (SLI) υsℓ plays an important role in crystallization/melting processes, and is one of the fundamental concepts of materials science. Based on the analysis of kinetic models of melting/crystallization with diffusion and collisional-thermal confinement, a modification of the transition state theory is performed, which forms the basis of the Wilson - Frenkel kinetic model developed at the beginning of the 20th century. The modification consists in replacing constant coefficients in the forward and reverse transition rates with a functional temperature dependence of the solid/liquid interface Tsℓ. Using 2 EAM interaction potentials for Al and Cu and the molecular dynamics method, atomistic modeling of melting/crystallization of metals (Al, Cu) under conditions of deep overheating/overcooling has been performed. By comparing the results of atomistic modeling with the data of the modified kinetic model for both metals, the temperature dependences of the response function υsℓ in the region of maximum permissible values of overheating/undercooling are constructed. The modification of the Wilson - Frenkel model is essentially a new kinetic model and allows one to obtain for metals the temperature diffusion-limited dependences of the velocity of the interface υsℓ, described by the same equation in the entire temperature range. The temperature dependences of the solid / liquid interface velocity, determined from the results of modeling using both interaction potentials, demonstrate a clear asymmetry with respect to the melting point Tm, which is explained by the strong difference between the solidification kinetics in a strongly undercooled state and the kinetics of melting in a highly superheated state. This work was supported by RSF, project 18-11-00318.

Resume : The kinetic theory of absorption of ultrashort laser pulses by ensembles of metal nanoparticles of spheroidal shape in the conditions of plasmon resonance is constructed. For the particles of the oblate or prolate spheroidal shape, the dependence of the absorbed energy on a number of variables, including a particle volume, a degree of the shape deviation from a spherical one, a laser pulse duration, and the value of shift of the carrier frequency of a laser ray from the frequency of the surface plasmon excitation in a spherical particle, is found. The analysis of the dependence of the energy absorbed by a spheroidal metal nanoparticle is carried out for the different values ​​of laser pulse duration and frequency identical to the surface plasmon resonance frequency. For the case of spheroidal metal nanoparticles with increase in the laser pulse duration, the peak of the dependence of the absorption splits into two peaks located on the opposite sides of the value corresponding to the plasmon resonance frequency. At the degree of prolateness or oblateness increases, the distance between the doublet components grows. The obtained theoretical results can be useful for the analysis of experimental data on the optical characteristics of metal nanoparticles in different dielectric media.

Resume : Food monitoring is becoming increasingly important, as health issues relating to the contamination of food by various analytes are becoming increasingly more prominent. Food can be contaminated or misused at any stage of the production chain, therefore, there is a need for detection methods that not only produce fast and reliable results but also have the potential to be implemented in portable devices that can be deployed at the Point-of-Need. Electrochemical sensors are increasingly used for the detection of various analytes (pesticides, mycotoxins, plasticizers etc...) in food, since they can provide rapid and reliable detection without the need for expensive instrumentation and skilled personnel required by conventional analytical techniques [1,2]. Herein, we describe the use of Laser Induced Forward Transfer (LIFT) utilizing a 355 nanosecond laser for the highly precise functionalization of SPEs for the fabrication of two different types of electrochemical sensors for the detection of pesticides and plasticizers in olive oil. As far as the detection of pesticides is concerned, the developed sensor is based on the inhibition of Acetylcholinesterase immobilized in a chitosan-carbon black matrix. For the detection of plasticizers, on the other hand, aptamers were used. Both type of sensors were developed with the use of the LIFT technique that possesses significant advantages in comparison to the conventional drop-casting method for sensor fabrication. With LIFT bio-printing [3, 4], delivery of the biomolecules and/or the signal enhancement matrix can be achieved in one step, with high special resolution, thus allowing extremely small electrode surfaces to be printed, ultimately reducing consumables’ wastage. Moreover, due to the high impact pressure of the transferred droplets at the receiver substrate, the physical adsorption of the biomolecule mixture onto the surface is enhanced, improving the electrochemical communication with the screen printed electrodes. Employment of the optimized sensor fabrication protocols allowed the sensitive detection of both carbamate and organophosphate pesticides in pretreated olive oil samples at values below the legislation limit of 10 ppb, whereas DEHP and DINP could be identified, following a simple olive oil sample pretreatment with the use of the LIFT-spotted aptamer-based sensor. [1] Pérez-Fernández, Β., Costa-García, Α., and De la Escosura- Muñiz, A., Biosensors, 10, 32(2020) [2] D. Soulis, M. Trigazi, G. Tsekenis, C. Chandrinou, A. Klinakis and I. Zergioti, Molecules, 25, 4988 (2020) [3] Chatzipetrou, M., Milano F., Giotta L., Chirizzi D., Trotta M., Massaouti M., Guascito M.R., Zergioti I., Electrochemistry Communications, 64, 46-50(2016) [4] Chatzipetrou, M., Tsekenis, G, Tsouti, V, Chatzandroulis, S., Zergioti, I., Applied Surface Science, 278, 250-254(2013)

Resume : Bacterial biofilms are multicellular communities adhering to surfaces and embedded in a self-produced extracellular matrix. Due to physiological adaptations and the protective biofilm matrix itself, biofilm cells show enhanced resistance towards antimicrobial treatment. In medical and industrial settings, biofilms e.g. on implants or on surfaces in food-processing industry can be a fertile source of bacterial pathogens and are repeatedly associated with persisting, nosocomial and foodborne infections. As extensive usage of antibiotics and biocides can lead to the emergence of resistances, various strategies are currently developed, tested and improved to realize anti-bacterial surface properties through surface functionalization steps avoiding antibiotics. In this study, contact-less and aseptic large-area ultrashort laser scan processing is employed to generate different surface structures in the nanometer- to micrometer-scale on technical materials, i.e. titanium-alloy, steel, and polymer. The processed surfaces were characterized by optical and scanning electron microscopy and subjected to bacterial colonization studies with Escherichia coli test strains. For each material, biofilm results of the fs-laser treated surfaces are compared to that obtained on polished (non-irradiated) surfaces as a reference. Depending on the investigated surfaces, different bacterial adhesion patterns were found, suggesting an influence of geometrical size, shape and cell appendages of the bacteria and – above all – the laser-processed nanostructure of the surface itself.

Resume : Inter-pulse accumulation of heat could affect the chemical and morphological properties of the laser processed material surface. Hence, the laser pulse repetition rate may restrict the processing parameters for specific laser-induced surface structures. In this study, the evolution of various types of laser-induced micro- and nanostructures at various laser fluence levels, effective number of pulses and at different pulse repetition rates (1 – 400 kHz) are studied for common metals/alloys (e.g. steel or titanium alloy) irradiated by near-infrared ultrashort laser pulses (925 fs, 1030 nm) in air environment. The processed surfaces were characterized by optical and scanning electron microscopy (OM, SEM), energy dispersive X-ray spectroscopy (EDX) as well as time of flight secondary ion mass spectrometry (TOF-SIMS). The results show that not only the surface morphology could change at different laser pulse repetition rates and comparable laser fluence levels and effective number of pulses, but also the surface chemistry is altered. Consequences for medical applications are outlined.

Resume : Anisotropic etching of crystalline materials is well known and has been studied for silicon using various organic and inorganic wet etchants. Due to these crystallographic etching mechanisms smooth, well defined 3D structures such as pyramidal structures can be obtained in monocrystalline <110> silicon. Potential applications are related to micromechanics or antireflection texturing for photovoltaics. Since wet etching processes feature some disadvantages, the development of anisotropic dry etching processes could be useful for future technologies aiming to higher integration avoiding wet chemical processing. This work a laser-based technique for anisotropic dry etching of <110> silicon using an ultra-short pulse laser source is proposed and demonstrated. Therefore, a micro plasma is generated by an optical breakdown in an CF4/O2 gas mixture with a pressure of 600-800 mbar that interact with silicon to form volatile products by chemical reactions of the plasma species with the silicon surface. The influences of different process parameters such as substrate temperature, crystallographic orientation, gas composition and pulse energy were investigated. Correlations between the etched surfaces features and the process parameters were extracted from topographical, geometrical as well as morphological studies using SEM imaging and AFM measurements. The present work shows that it is possible to etch pyramidal structures into (100)-silicon.

Resume : Silicon carbide composite (SiC/SiC) is a high-tech material with extraordinary characteristics that is useful for different applications in aerospace, light wight construction and car industry. The machining of this SiC/SiC composite material is challenging due to the hardness and brittleness. Therefore, often near surface defects are formed caused by the machining processes. Laser machining enable new approaches for machining. However, laser machining makes often use of ablation processes that cause damage to the material too. Here we propose and demonstrate a new approach for gentle SiC/SiC machining making use of a laser-induced plasma for reactive species generation. The generated reactive species enabling a chemical reaction-based material removal process. A fs-laser (775 nm, 150 fs, 1 kHz) was focused in a CF4/O2 gas mixture igniting a laser induced plasma (LIP) in front of a SiC/SiC sample. The plasma – surface distance was approximately 130 µm. This LIP initiate material removal processes of the multiphase SiC/SiC sample without a mechanical damage of the SiC composite structure. Different surface features such as etching of the cover SiC layer, etching of the SiC matrix and exposure, thinning and sharpen of the SiC fibres, underetching of the fibres, was observed. Across the whole etched area, no mechanical damage such as cracks, delamination’s, broken fibres were observed so that a gentle machining process can be expected. The present work shows first results and discussing potential application of this machining approach.

Resume : Tashkent Films of manganese silicides on silicon, obtained in a high-vacuum reactor, which was supported by a high-speed pumping system (450 l•c-1). In the manufacture of the HSR film, silicon KDB-10 or KDB-3000 with orientation (111) and polycrystalline silicon KDB-0.1 were used as a substrate. Before loading into the reactor, the surface of the samples was polished by mechanical and chemical methods. Evaporation of twice sublimated manganese occurred in the reactor at Т1130°С for 15-20 min. It was found that the Hall coefficient is positive over the entire temperature range under consideration, the carrier concentration is p  1020 cm-3, and the Seebeck coefficient. depending on Tpod was  = 150-200 µV / K, and electrical conductivity  = 10-15 (Ohm∙cm)–1. To study the speed  and the conversion coefficient S, the films were placed in a shielded case, and the thermoelectric power that appears at the contacts of the film during its irradiation was fed to the input of an oscilloscope or measuring amplifier. It was found that HSR films with a thickness of 5-7 µm on silicon substrates have a speed of   10–6 s, and the conversion coefficient S, regardless of the radiation wavelength, was more than 500 µV / W. The technical parameters of the HSR films are as follows: - the spectral sensitivity range extends from 0.2 to 200 µm, - the conversion coefficient S = 500–2000 µV / W at the radiation length  = 10.6 µm, - the thermoelectric coefficient.   300 µV / K, - time constant (response speed)   10–6 c, - element electrical resistance no more than 200 Ohm.

Resume : Spectrally selective solar cells can be utilized in novel photovoltaic (PV) applications like colored windows or agrivoltiacs. Recently, we demonstrated that the combination of a metal-oxide multilayer electrode with an ultrathin germanium solar cell leads to spectrally selective transmission [1]. However, the innovative contact and the ultrathin absorber lead to new challenges for the laser processes used for monolithic interconnection, which are necessary to fabricate PV modules. In this study, we show experimental results of the three laser scribing steps P1, P2 and P3 that we use to process PV mini modules. Especially, we focus on the P2 scribe, which is the ablation of the ultra-thin germanium absorber layer through the semi-transparent electrode. We compare the ablation process for a spectrally selective electrode with two silver layers to a standard AZO electrode. We consider different laser wavelengths and powers for the ablation process. The laser cuts were analyzed by optical microscopy and SEM. [1] Osterthun, Norbert, et al. "Spectral engineering of ultrathin germanium solar cells for combined photovoltaic and photosynthesis." Optics Express 29.2: 938-950.

Resume : In majority of laser micromachining applications Gaussian mode is most common and versatile. However, some form of beam shaping can improve various laser related processes. For example, due to a long diffraction-less focal region Bessel beams proved to be beneficial in transparent material laser micromachining and their applicability is steadily expanding. Variations of nondiffracting Bessel-like beams having different transverse intensity distributions such as parabolic and elliptical beams also exist and find their use too. We demonstrate generation of high aspect ratio beams with complex transverse intensity distribution that can be obtained by superimposing several higher order Bessel beams also known as Bessel vortices. Introducing different cone angles of the interfering beams allows for further modifications of the resulting profile. In this work we present a technique for generating superimposed higher-order Bessel beams of different spatial frequencies and topologies. We first experimentally tested our simulations for superimposed beams using spatial light modulator. We then inscribe a beam shaping mask inside fused silica sample to create a geometrical phase element. Lastly, we demonstrate the ability to use geometrical phase elements and superimposed beams to obtain high aspect ratio modifications inside various glasses.

Resume : Laser-direct writing of graphene structures on different polymeric sources has been demonstrated to be a potential approach to produce, among others, micro-supercapacitors, nano-generators or sensors. Laser-induced graphene is produced on the surface of polymers by using, in general, laser radiation emitted by CO2 lasers due to the good absorption of most polymers to this laser radiation. The fast thermal decomposition and carbonization of the laser irradiated surfaces lead to the formation of graphene. In this work, we have studied the capabilities of other laser sources emitting ns- or ps- pulses to produce graphene on some polymers. These are able to produce graphene patterns with a higher resolution, and finer details can be produced. Finally, we demonstrate the capability of this graphene to be used as temperature sensors.

Resume : Pancharatnam-Berry phase elements (PBPE)and their applications are booming nowadays: from devices like high NA metalenses to special optics like top-hat elements, from wavelengths in the ultraviolet to the THz diapason. The reason behind such flexibility is due to the variety of different production approaches - lithography-based, sculptured coatings or inscribed in glasses by femtosecond laser pulses. Due to the varying orientation and individual properties of sub-elements of the PBPE such elements act as both scalar and vectorial diffractive optical elements (or as shapers of the spatial spectra of the input beam), but usually their vectorial properties are largely ignored due to the complexity of mastering phases and amplitudes of both transverse components. Here, we build upon a phase-based implementation of the top-hat converter and propose a new approach, which enables us to increase the efficiency of the top-hat converter. We propose to employ the vector nature of geometrical phase elements and demonstrate how phase masks together with the polarization of the incident beam enable us to achieve high efficiencies. We report on our systematic numerical study on the efficiency and feasibility of such elements. Moreover, we use a femtosecond laser-based setup developed by “Altechna R&D” (“Workshop of Photonics”, see Special Optics) to inscribe nano-gratings in the bulk of the glass. By controlling the orientation and retardance of those nano-gratings we effectively manufacture a PBPE, where the Gauss to top-hat converter is implemented efficiently. Lastly, we present an experimental study on top-hat converters, which were fabricated using a new encoding technique.

Resume : A combination of beams exhibiting long focal lines and small focal spot sizes is desired in a variety of applications. A good example is laser micromachining of structures with dimensions comparable to the wavelength of incident light. Optical beams exhibiting this property are called optical needles, with Bessel beam being a common example. Conical prisms are commonly used to generate Bessel beams, so a combination of axicons together with passive optical apodization components flattens the on-axis intensity profile and reduces on-axis oscillations. A good example of such alteration is known as the logaritmical axicon, which is usually designed employing principles of geometrical optics. Here, we consider optical elements based on the space-domain Pancharatnam–Berry phase (PBP). Unlike diffractive and refractive elements, the phase here is not introduced through optical path differences but results from the geometric phase that accompanies space-variant polarization manipulation. Our implementation is based on type 2 modification of bulk transparent material, resulting in formation of nanogratings with fast axes aligned perpendicular to the grating corrugation. By spatially varying fast axis direction of nanogratings in respect to incoming electric field vector any phase element can be emulated. Here we numerically evaluate Fresnel diffraction from a specially designed PBP element and form an optical needle with Bessel-like transverse profile and its longitudinal size exceeding transverse by few hundred times. Our experimental implementation is based on PBP elements produced by “Altechna R&D” with their transmittance being higher than 90% in a broad-spectrum region ranging from 380 nm to 1100 nm. Lastly, we investigate both numerically and experimentally stability of optical needle generation on elipticity of the incident Gaussian beam, on the misalignment of propagation axis and center of the element, on the rotated polarization of the incoming beam etc.

Resume : One of the challenges for laser micromachining technologies is the beam shape and its longitudinal profile, which makes a huge impact on the efficiencies of processes. Airy beam has a unique beam shape because its Rayleigh length is considerably bigger when compared to a Gaussian beam. Also, its intensity peak travels along a curved trajectory during the beam propagation. Curved trench machining is proved to be possible using Airy beams. They also can enhance resolution in light-sheet microscopy. We have employed an optical system for beam shaping which was based on geometric phase optical elements (GPOE). Out implementation is based on nano-gratings inscribed by femtosecond pulses (technology by “Altechna R&D”). In these GPOEs spatial profile of phase and retardance is induced by space-variant self-assembled birefringent fused silica modifications of the second type. We study, how the coefficient of the mask for Airy beam generation determines the resolution (or fine structure) of the GPOE. The smaller the curvature, the longer the trajectory and vice versa. However, as the technology has its own spatial resolution, we study also different methods to produce a mask: phase and amplitude-only, binary and gradient-like. As we study efficiencies of different methods, we encounter yet another problem – an appearance of the undiffracted zero-order beam, which interferes with an intensity peak of a diffracted Airy beam. Both simulations and experiments show that combining phase masks for Airy beam generation with linearly-variant and quadratically-variant phase masks induce displacement of an Airy beam transversely and longitudinally, respectively. Thus, we can separate the beam from the zeroth-order (undiffracted) beam.

Resume : Femtosecond laser texturing creates a set of hierarchical micro and nanostructures on solid surfaces allowing a control over their wettability. One of the promising applications of this effect is in the integration and durability of dental and orthopedic implants. It is still unclear, however, why and how the wettability of laser textured surfaces changes with time. The classical models, such as the Wenzel and Cassie-Baxter, have not provided enough explanations and a more realistic study is required. In this work, we used a continuum-level modelling method to study the wetting dynamics of a water droplet on Ti and Ti alloy. The wetting studies were performed on both plain solid surfaces and on surfaces with various reliefs. The calculated evolutions of the contact angle with time for both structured and non-structured surfaces provide explanations of several experimental results. Such simulations are shown to be promising for explaining the wetting mechanism for laser textured materials. [1] A. Klos, X. Sedao, T.E. Itina, C. Helfenstein-Didier, C. Donnet, S. Peyroche, L. Vico, A.Guignandon, V. Dumas, Nanomaterials 2020, 10, 864. [2] J. Du, Y.Zhang, Q Min, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 609, 2021, 125649.

Resume : The lithium–sulfur (Li-S) battery is a promising next-generation rechargeable battery with high energy density. Given the outstanding capacities of sulfur (1675 mAh g–1) and lithium metal (3861 mAh g–1), Li-S battery theoretically delivers an ultrahigh energy density of 2567 Wh kg–1. However, this energy density cannot be realized due to several factors, particularly the shuttling of polysulfide intermediates between the cathode and anode, which causes serious degradation of capacity and cycling stability of a Li-S battery. In this work, a simple and scalable route was employed to construct freestanding laser-scribed graphene (LSG) interlayer that effectively suppresses the polysulfide shuttling in Li-S batteries. Thus, a high specific capacity (1160 mAh g–1) with excellent cycling stability (80.4% capacity retention after 100 cycles) has been achieved due to the unique structure of hierarchical three-dimensional pores in the freestanding LSG.

Resume : TiO2 is one of the most studied materials due to its non-toxicity, environment friendliness and corrosion resistance. It has found many applications, especially in the field of biomedicine and biotechnology, environment technology or photochemistry. However, in some environments thin passivation layer is not enough protection and treatment promoting the growth of the oxide layer even reaching several microns is required to increase the corrosion resistance. Typically, this goal is reached via anodization that under optimized conditions can lead to the fabrication of highly ordered nanotubes directly onto the Ti substrate and simultaneously enables to control their geometric features. Titania nanotubes (TiO2 NTs) provide unique properties related to high electron mobility, high specific surface area and enhanced light absorption. Therefore, many works are focused onto titania NTs regarding them as an ideal platform for further modifications. Most of them concern doping or decorating titania with non-metals (e.g. B, I [1]) or metals (e.g. Au, Ag, Cu [2]) as well as conducting polymers, dyes and metal oxides. Less obvious route to alter TiO2 optical properties is by introducing nanoparticles containing rare earth elements [3] and further leaser treatment leading to their encapsulation inside the TiO2 NTs. Herein, we present novel material based onto well-separated TiO2 nanotubes decorated with three different nanophosphors. First, electrochemical anodization was utilized in order to obtain hierarchical structure composed of laterally spaced NTs. As-prepared substrates underwent thermal treatment to ensure anatase crystalline phase and material was covered with rare earth vanadate and fluoride matrices doped with Eu3+ or Yb3+/Er3+ ions. In the final step of fabrication procedure, laser annealing was utilized for selective closing of NTs tops [4]. SEM inspection revealed the complete coverage of NTs by phosphors as well as the formation of tight caps over chosen area. The presence of nanophosphors coatings was also confirmed by Raman measurements as well as the optical investigations by means of UV-Vis spectrophotometer and NIR laser system. In addition, an exposure of modified nanotubes to the light of a UV lamp or NIR laser showed red and green emission, visible by naked eye, of a shape defined by the mask used during laser treatment. Obtained results confirmed that the laser-assisted modification of titania nanotubes decorated with rare earth elements can open a new way for unique marking. This work was financed by National Science Centre (Poland) via grant no 2017/26/E/ST5/00416 and The National Centre for Research and Development via grant no LIDER/39/0141/L-9/NCBR/2018. [1] K. Siuzdak et al., New Journal of Chemistry 39 (2015) 2741-2751 [2] K. Grochowska et al., Scientific Reports 10 (2020) 20506 [3] A. Szczeszak et al., Journal of Materials Chemistry C 8 (2020) 11922 [4] J. Wawrzyniak et al., Scientific Reports 10 (2020) 20235

Resume : The work proposed herein investigates the possibility of using clay thin films, prepared by laser techniques, as absorbents for allergen proteins found in eggs. Thin films of lamellar clays were deposited by laser techniques (matrix assisted pulsed laser evaporation (MAPLE) and pulsed laser deposition (PLD)). The main property of these materials is the adsorption capability, which is connected to the layer charge density and swelling characteristic. The considered clays were layered double hydroxides and kaolinite. Chemical, structural and morphological properties of the clay-based films were investigated in order to identify the absorption mechanism and capabilities.

Resume : Developing cost-effective devices based on p-type wide-bandgap semiconductors operating at deep UV (UV-C) spectral range is still challenging. This motivated us to explore wide-bandgap p-type MnO quantum dots (QDs) (with the bandgap of ≈ 5 eV) synthesized by femtosecond pulsed laser ablation in liquid (FLAL), which is a cost-effective technique. In this study, we demonstrate photodetectors based on p-MnO QDs. MnO target in ethanol was ablated by ultrafast Ti:Sapphire laser (800 nm and 75 MHz) to synthesize the wide-bandgap p-MnO QDs under ambient conditions.[1,2] We subsequently demonstrated the p-type conductivity of the QDs using the Kelvin probe (KP), as well as via field-effect transistor (FET) measurements. X-ray diffraction (XRD), transmission electron microscopy and Raman spectroscopy were also performed to ascertain the MnO QD composition. Absorption spectroscopy indicated that the bandgap was in the 4.8−5 eV range. The solution-processed MnO QDs are simply spray-coated on the interdigitated electrodes (IDE) SiO2 to fabricate MnO-based solar-blind deep-UV photodetector. As proof of concept, a high‐performance, self‐powered, and solar‐blind Schottky DUV photodetector based on such QDs is fabricated, which is capable of detecting under ambient conditions. The carrier collection efficiency is enhanced by asymmetric electrode structure, leading to high responsivity. Electrical and photocurrent analyses reveal a good photocurrent response (227 mA/W) under 244 nm laser illumination with a cut-off below 300 nm. The Self-powered characteristic is demonstrated by operating the photoreactor under 0V. The highly stable p‐type and crystalline nature of the p-MnO QDs would be immensely beneficial for a wide range of applications in electric and optoelectronic devices.

Resume : Increased selectivity, response speed, and sensitivity in the chemical and biological determinations of gases and liquids are arguably an important step towards future micro and nano sized sensing systems. Since their development by White and Voltmer in 1965, surface acoustic wave (SAW) devices have attracted much research attention due to their unique functional characteristics which make them appropriate for the detection of chemical and biological species. This work surveys our latest progress in laser printing engineered complex materials, i.e. graphene functionalized with monoclonal antibody anti-alpha-fetoprotein, for applications as recognizing elements in miniaturized surface acoustic wave sensor design and application. Here, graphene functionalized with monoclonal antibody anti-alpha-fetoprotein have been printed by laser induced forward transfer (LIFT) into 2-dimensional pixels onto the active surface of a SAW platform. First, a parametric study (i.e. laser fluence, donor film morphology and thickness as well as single versus multiple pixel deposition) was carried out to determine the optimum experimental conditions under which sensitive pixels are obtained. Following the morphological and structural characterization of the laser printed material, the responses of the coated SAW resonators are measured. The sensitivity of the monoclonal antibody anti-alpha-fetoprotein functionalized graphene coated SAW devices gives an indication these devices represent an enabling technology for monitoring liver damage. Acknowledgement Financial support from i) NILPRP through the NUCLEU program and ii) UEFISCDI, though the PN-III-P2-2.1-PED-2019-1603 (SAWSENSE) project are gratefully acknowledged.

Resume : We study femtosecond laser interactions in various bandgap materials at non-conventional driving wavelengths from the deep-ultraviolet to the mid-infrared part of the spectrum. The range of nonlinear responses accessible by radiation tuning allow to revisit questions as important as the achievable resolution in laser machining technologies. In particular, we establish that the concept of nonlinear resolution is not applicable for femtosecond laser ablation. Independently of the nonlinearity of interaction, we find a systematic one-to-one mapping between femtosecond laser ablation features in dielectrics and beam contours at a strict threshold-intensity. This is because any observable based on threshold-based response (as ablation) simply ruins all potential benefits that could be expected on resolution from the nonlinear confinement of absorption. Accordingly, the use of extreme UV should not be overlooked to reach the nanoscale resolutions routinely achieved in lithography. At the opposite side of the spectrum, ultrashort infrared laser pulses open opportunities to tailor in the three dimensions (3D) some semiconductors inside which breakdown regimes were inaccessible until recent demonstrations. Our first proposed solution uses hyper-focused beams to demonstrate permanent modifications in the bulk of silicon with sub-100-fs. For more practical alternatives, we rely on optimizations in the time domain. We generate and apply ultrafast trains of pulses at the highest achievable repetition-rates (up to THz). This introduces unique multi-timescale control parameters used for improved energy deposition and reliable 3D laser writing deep inside silicon chips.

Resume : Carbon-atom wires are finite linear chains based on sp-carbon hybridization and show appealing properties for energy and electronic applications [1]. These nanostructures exist in two different configurations: one with alternated single and triple bonds, called polyyne, and one with a sequence of double bonds, named cumulene. Among the large variety of available synthetic methods, pulsed laser ablation in liquid (PLAL) is a scalable physical technique which allows the synthesis of hydrogen-terminated polyynes which suffer from a limited stability [2]. Encapsulation of polyynes in a polymeric matrix is a good strategy to improve their stability and to create new functional materials. In the work here presented, we developed PLAL for the in situ synthesis of polyynes directly in a polymer matrix. Specifically, we ablated graphite in a solution of poly(vinyl alcohol) (PVA) [3] or polymethylmethacrylate (PMMA) at different concentrations by a Nd:YAG nanosecond pulsed laser at 532 nm. Ag nanoparticles were added to polyynes/polymer mixtures in order to structurally characterized by surface-enhanced Raman spectroscopy (SERS) both the polymeric solutions and the free-standing films, which were obtained after solvent evaporation. The nanocomposites were also morphologically analysed by scanning electron microscopy and the stability of polyynes encapsulated in the polymer was investigated. We observed improvements both in the yield of carbon-atom wires by laser ablation in polymeric solutions and in the stability of polyynes if embedded in PVA or in PMMA. By this way, we here propose a novel strategy for the preparation of new functional materials for future industrial applications. [1] C.S. Casari and A. Milani, MRS Comm., 8, 207, 2018. [2] S. Peggiani et al., Chemical Physical Letters, 740, 137054, 2020. [3] S. Peggiani et al., Materials Advances, 1, 2729, 2020.

Resume : The application of metals in the form of nanostructured antimicrobials is continuously expanding. In the last decades, especially Ag-based nanoantimicrobials 1 have attracted the interest of scientists, as assessed by the huge number of reports on their synthesis and characterization 2. Designing bioactive materials, with controlled metal ion release, exerting significant biological action and associated to low toxicity for humans, is nowadays one of the most important challenges for our community. The most looked-for nanoantimicrobials are capable of releasing metal species with defined kinetic profiles, either slowing down or inhibiting bacterial growth and pathogenic microorganism diffusion. In recent years, we have developed and deeply characterized many different nanoantimicrobial systems, ranging from Ag-modified textiles 3 to bioactive food packaging 3. On the one hand, all these materials were found to be human safe since they showed no significant leaching of (potentially toxic) whole nanoparticles into contact media. On the other hand, antibacterial ionic species released by transition metal nanophases provided a powerful alternative route to fight bacterial resistance towards conventional antibiotics and disinfecting agents. Laser ablation synthesis in solution (LASiS) has been used in our labs to produce bioactive Ag-based nanocolloids, in isopropyl alcohol, which can be used as water-insoluble nano-reservoirs in composite materials 4. In fact, including nanophases into polymers (like polyethylene oxide or poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) allows to produce multifunctional packaging, combining biodegradable and antibacterial properties of both organic and inorganic phases 5. In this study, infrared spectroscopy was used to evaluate the chemical state of pristine nanoparticles and final materials, providing useful information about synthesis processes, as well as storage and processing conditions. Transmission electron microscopy was exploited to study morphologies of nano-colloids, along with UV-Vis for bulk chemical characterization. Electrothermal atomic absorption spectroscopy was used to investigate metal ion release from modified surfaces and industrial products. Analytical spectroscopy results were matched with bioactivity tests on target microorganisms of food spoilage. Different approaches to the synthesis and characterization of 2nd-generation nanoantimicrobials, e.g., to those materials combining antibacterial efficiency and nanosafety issues, will be critically discussed, based on spectroscopic, morphological, release and bioactivity evidence. References: 1. M.D. Dizaj et al., Mat. Sci. Eng. C (2014), 44, 278–284. 2. M.C. Sportelli et al., TrAC (2016), 84A, 131-138. 3. M.C. Sportelli et al., Applied Surface Science (2020), 507, 145156. 4. M.C. Sportelli et al., Food Packaging and Shelf Life (2019), 22, 100422. 5. S. Raho et al., Foods (2020), 9, 1459.

Resume : Palladium nanoparticles are widely used because of their extraordinary catalytic and electronic features. Regarding the biomedical field, they are commonly used in dentistry appliances, sensors for detection of diverse analytes and as part of cancer therapy. In this work, Pd nanoparticles are obtained by laser ablation of solids in liquids (LASL) technique, in order to investigate their antibacterial activity. Colloidal solutions of nanoparticles were prepared by ablating a palladium foil submerged in distilled de-ionized water and methyl alcohol, using a nanosecond Nd:YVO4 laser operating at 532?nm and a picosecond Nd:YVO4 operating at 1064 nm. Synthesized nanoparticles were characterized by means of Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), UV?Vis spectrophotometry and X-ray diffraction (XRD). The kinetics of palladium ions release was tracked during the first 14 days by means of Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Finally, the obtained nanoparticles were deposited on medical grade titanium discs in order to evaluate their antibacterial activity against S. aureus. The obtained colloidal solutions resulted mainly in crystalline Pd nanoparticles, rounded in shape and ranging from few to hundreds of nm. The nanoparticles size are more homogeneous when nanosecond laser is used, and it decreases if methyl alcohol is used as solvent. Synthesized Pd nanoparticles exhibited different inhibitory effect on bacteria. These results demonstrate the influence of size, crystallography, stability and ion release kinetics of palladium nanoparticles on their biocidal activity.

Resume : Functional coatings are finding high value applications in numerous technological fields, especially when involving nanocapsules systems for the release of active agents. Traditional deposition methodologies often produce poor quality coatings due to nanoparticle agglomeration, moreover temperature or solvents involved may damage sensitive bio-based polymers. In this scenario, Matrix Assisted Pulsed Laser Evaporation (MAPLE) technology is able to preserve the integrity of polymeric materials while controlling thickness, composition, and uniformity of the coating. The presented work reports on the use of two families of polymeric nanocapsules: azobenzene-based photo-responsive polyamide nanocapsules and biocompatible/biodegradable PLGA nanocapsules loaded with functional substances. The successful deposition of the capsules on various substrates was confirmed by Infrared Spectroscopy, Scanning Electron Microscopy and Atomic Force Microscopy. The active coatings were then tested as delivery platforms for the encapsulated active agents and release behaviour was monitored via UV-vis spectroscopy. Photo-responsive capsules were able to release the cargo material by application of a visible light-source, while sustained release in PLGA-based capsules occurred due to their erosion and biodegradation. Overall, MAPLE technique qualifies as a laser-based technique with potential use also in applications such as food packaging, anticorrosion coatings and biomedical devices.

Resume : The latest advances in graphene and other 2D materials have disrupted, among others, the field of flexible electronics and sensors. At the same time, the precise and intact deposition of 2D materials still pose a great challenge. The Laser Induced Forward Transfer (LIFT) technology has been reported as a reliable, high resolution and digital fabrication tool for flexible electronics, sensors and optoelectronics [1,2]. Here, we report on the use of LIFT for the transfer of CVD-grown, single layer graphene at predefined areas with high resolution, with Raman Spectroscopy, AFM and SEM characterization confirming the transfer of high-quality graphene pixels (2D over G ratio >2). Moreover, a flexible touch sensor, in a parallel plate capacitor configuration will be presented and will demonstrate the controllable and defect-free transfer of graphene electrodes with area as large as 1 mm2, with Ag nanoparticles (NP) as bottom electrodes, a 3 μm-thick PDMS layer as the dielectric and graphene as the top electrode. Four-point probe IV measurements yield a sheet resistance in the order of 500 Ohm/sq, while preliminary capacitance measurements of the touch sensor exhibit values in the order of 2-4 pF. Also, more than 50% increase of capacitance, owing to the deformation of the dielectric’s thickness when stress is applied on the configuration is demonstrated. These results are promising for the development of sensitive graphene-based touch sensor with thin, flexible and lightweight form factors. [1] Laser Induced Forward Transfer of high viscous, non-Newtonian silver nanoparticle inks: Jet dynamics and temporal evolution of the printed droplet study, Ioannis Theodorakos, Agamemnon Kalaitzis, Marina Makrygianni, Antonios Hatziapostolou, Ayala Kabla, Semyon Melamed, Fernando de la Vega and Ioanna Zergioti, Adv. Eng. Mater., (2019) [2] Copper micro-electrode fabrication using laser printing and laser sintering processes for on-chip antennas on flexible integrated circuits, O. Koritsoglou, I. Theodorakos, F. Zacharatos, M. Makrygianni, D. Kariyapperuma, R. Price, B. Cobb, S. Melamed, A. Kabla, F. de la Vega,and I. Zergioti, Opt. Mater. Express 9, 3046-3058, (2019)

Resume : More and more efforts are being done in order to fabricate functional surfaces with an increased number of applications. In particular, the fabrication of structures in the micro- and nanoscale allows the design of materials with advanced surface properties. Examples of complex structures possessing specific functions and properties may be found in nature. For instance, the control of wettability by the presence of hierarchical surface structures ranging from micro to the nanometer scale, may provide self-cleaning properties as the lotus leaf does in nature; hierarchical structures play also a role in the excellent adhesion of the gecko feet, and the presence of anisotropic micro and nanostructures affect the friction as it happens in the snake skin. In order to obtain complex structures, different strategies have been developed based on chemical etching, lithographic techniques, or template-based methods. Laser-based methods have demonstrated to be effective in the fabrication of surface micro- and nanostructures which find a wide range of applications such as cell culture, sensors or controlled wettability. One laser-based technique used for micro- and nanostructuring of surfaces is the formation of laser induced periodic surface structures (LIPSS). LIPSS are formed upon repetitive irradiation at fluences well below the ablation threshold and in particular, linear structures are formed in the case of irradiation with linearly polarized laser beams while irradiation with circularly polarized lasers gives rise to the formation of circular nanostructures. In this work, we report on the simple fabrication of a library of ordered nanostructures in a polymer surface by repeated irradiation using a nanosecond pulsed laser operating in the UV and visible region in order to obtain nanoscale controlled functionality. By using a combination of pulses at different wavelengths and sequential irradiation with different polarization orientations, it is possible to obtain different geometries of nanostructures, in particular linear gratings, grids and arrays of nanodots. We use this experimental approach to nanostructure the semiconductor polymer poly(3-hexylthiophene) (P3HT) and the ferroelectric copolymer poly[(vinylidenefluoride-co-trifluoroethylene] (P(VDF-TrFE)) since nanogratings in semiconductor polymers as P3HT and nanodots in ferroelectric systems are viewed as systems with potential applications in organic photovoltaics or non-volatile memories.

Resume : Amorphous chalcogenides are non-crystalline materials with considerable infrared transparency and high optical nonlinearities. They also possess various types of photoinduced phenomena when exposed to near bandgap light. Radio-frequency magnetron co-sputtering technique with a confocal geometry enables the fabrication of thin films with various compositions having considerable optical quality. One may easily examine pseudo-binary compositions of various molar ratios simply applying different electrical power on the individual cathodes. Thin films of amorphous Ge-Sb-Se ternary system of desired optical quality were obtained by co-sputtering technique. Linear optical properties, specifically refractive indices and optical bandgap energies, were obtained by spectroscopic ellipsometry employing Cody-Lorentz oscillator model. Subsequently, nonlinear optical properties by means of Kerr coefficient ? and the two-photon absorption coefficient ? of co-sputtered thin films are estimated from dispersion curves and optical bandgap energies. Furthermore, the influence of prolonged near bandgap light irradiation from suitable laser sources provides a valuable information about the photo-stability of these materials and hence their potential suitability for nonlinear optical applications in the near infrared domain.

Resume : Ferroelectric thin films have been intensively investigated in the last decades, owing to a combination of dielectric, electric and electromechanical properties with a wide spectrum of applications. It was recently shown that graphene-ferroelectric heterostructures can be successfully used in improving the functionalities of graphene-based transistors/devices. The qualities of the ferroelectric surface and of the growth/transfer process of graphene on it are key issues for obtaining nanoelectronic devices with enhanced properties and functionalities. Lead Zirconate Titanate (PZT) and HfO2 have been chosen as ferroelectric materials. A parametric study regarding the deposition of very thin layers (thicknesses in the nm range) directly on Silicon substrate, with very low roughness and appropriate ferroelectric properties was carried out. Another parametric study is related to properties modification by strain engineering for Y-doped BiFeO3 (Bi0.97Y0.03FeO3) films grown on Nb:SrTiO3(001) substrates. The layers photocatalytic activity was shown to strongly depend of epitaxial strain relaxation due to thickness variation.

Resume : In order to operate with high-power lasers, it is necessary to have high performing and resistant optics. The aim of this work is to test the resistance of antireflection coatings that can be used for ultra-short high-power lasers beam delivery/handling systems. At the present time, one of the biggest problems when operating high power lasers is the systematic damage coatings applied to various optical components. The use of antireflection (AR) coatings reduces the unwanted reflections from surfaces, keeping only the desired component, for which the reflectivity can reach up to 99.99%. In order to have high reflections for a range of wavelengths and diminished (antireflection) for another range, some more elaborate mirrors were developed. Generally, the optical coating is a dielectric material (e.g. metal oxide) deposited as thin film on optical support (quartz). The antireflection coatings are based on multi-layers with different refractive indices by pulsed laser deposition (PLD). The materials that were used are cheap and have repeatedly demonstrated their efficiency for this purpose: Hf, Al and Si oxides. In the frame of this work, heterostructures formed from 5 to 7 different layers should be tested to ultra-short high-power laser beam in order to determine the LIDT values and to advance their applicability in ultra-high peak power facilities.

Resume : Different types of laser-generated surface structures, i.e., Laser-induced Periodic Surface Structures (LIPSS, ripples), Grooves, and Spikes are generated on titanium and Ti6Al4V surfaces by means of femtosecond (fs) laser scan processing (790 nm, 30 fs, 1 kHz) in ambient air. Morphological, chemical and structural properties of the different surface structures are characterized by various surface analytical techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), Glow discharge optical emission spectroscopy (GD-OES), and depth-profiling Auger electron spectroscopy (AES). It is revealed that the formation of near-wavelength sized LIPSS is accompanied by the formation of a graded oxide extending several tens to a few hundreds of nanometers into depth. GD-OES performed on other superficial fs-laser generated structures produced at higher fluences and effective number of pulses per spot area such as periodic Grooves and irregular Spikes indicate even thicker graded oxide layers. These graded layers may be suitable for applications in prosthetics or tribology.

Resume : Selective laser melting (SLM) is recognized as a promising additive manufacturing technology nowadays. 3D printed part represents thousands of melted tracks that are obtained by the interaction of powder with the laser, formation of the melt pool, and solidifying. To obtain high-quality dense parts it is necessary to determine optimal laser parameters, i.e. laser power and scanning velocity. The purpose of the present research is to develop an optimization approach of the SLM process by characterizing the melt pool. Nickel-titanium (nitinol) powder was used in the present study due to the contradictory printing parameters found by different researchers and the high application potential in 3D printing of biomimetic scaffolds for medical implants. Among the materials used for implants, nitinol attracts increased attention by reason of the shape memory effect and excellent biocompatibility. Single tracks of the NiTi powder were printed using Trumpf TruPrint 1000 equipped with 200W continuous fiber laser (55 um laser spot). Chosen laser powers and scanning speeds cover the most combinations reported in the literature. Cross-sections of the single tracks were examined to determine the effect of printing parameters on the melt pool shape and evolution. Numerical simulation of the multiphase system involving solid powder and liquid melt pool was carried out using OpenFOAM software. The model taking into account the main interaction forces that play significant role in the SLM process. Additionally, the microhardness tests were done directly on the cross-sections of the single tracks. The results demonstrate that characterization and analysis of the melt pool provide useful information for optimization of the printing process. Microhardness values have singularities at some combinations of parameters. Further research will involve 3D printing of nitinol samples, mechanical properties comparison of linear and volumetric samples with subsequent development of the model.

Resume : Ultrafast laser welding is a proven technique which enables to bond a wide variety of materials together. This technique relies on laser energy deposition at the interface between two materials. While, to date, ultrafast laser welding has been demonstrated in numerous material configurations such as glass-glass, glass-semiconductor, glass-metal, polymer-polymer, and ceramic-ceramic, it has no equivalent for the semiconductor-metal configuration so far, which would be particularly interesting for applications in microelectronics. We explain the nonexistence of semiconductor-metal laser welding technique by the important nonlinear propagation effects before reaching the interface between the two materials. Nonlinear propagation imaging in silicon with 9.8-ps pulses at 1555-nm wavelength shows significant nonlinear focal shift values for pulse energies up to 1 µJ, in good agreement with a semi-analytical model based on self-focusing theory. We demonstrate that this nonlinear focal shift leads to a drastic depletion of the light intensity at the exit surface of silicon at levels insufficient for laser welding applications. The determination and the precompensation of the nonlinear focal shift allow us to maximize the light intensity at the interface between silicon and copper, leading to the very first demonstration of semiconductor-metal laser welding. A maximum shear joining strength of 2.2 MPa is measured between the samples. Given that this order of magnitude is also the one that can be obtained with laser welding in other material configurations as well as with other joining techniques, our proposed method holds high potential for applications. Ultimately, material analyses of the welds with electron microscopy and Raman spectroscopy shed light on the physical mechanisms involved during welding, which might include silicon amorphization, covalent bond creation, and surface plasmon excitation. Our proposed ultrafast laser welding technique relying on the precompensation of the nonlinear focal shift has the potential to be applied in numerous semiconductor–metal configurations. Moreover, we anticipate that this technique is also applicable in several semiconductor–semiconductor configurations where at least the first material is transparent to the laser wavelength.

Resume : Smart solar-blind deep-UV (DUV) photodetectors based on solution-processed quantum dots (QDs), operating in the UV-C range presently suffer from low responsivity including weak self-power performance. Here, we address this issue by demonstrating a method for fabricating an enhanced solar-blind DUV photodetectors based on solution-processed ZnO QDs functionalized by p-CuO micro-pyramids for the first time. The photodetector performance is optimized via a p−n junction structure. Self-assembled catalyst-free p-CuO micro-pyramid arrays are fabricated on a pre-ablated Si substrate by pulsed laser deposition while the solution-processed n-ZnO QDs are synthesized by femtosecond-laser ablation in liquid (FLAL) technique. The photodetector is fabricated simply by spray-coating ZnO QDs on a CuO micro-pyramid array. The photodetector is characterized by superior photo-responsivity at 244 nm (UV-C) with relatively fast photoresponse (< 80 ms) with a cut-off at 280 nm. The photoresponse photo-responsivity at 0 V, indicating a self-powered characteristic that can be due to a built-in electric field in the depletion layer. We show that p-CuO micro-pyramids contributed in performance enhancement. These high-performance solar-bind DUV photodetector arrays can be scaled up for mass production of a wide range of applications.

Resume : This study compares the weld quality of glass on silicon welding by nanosecond and femtosecond laser pulses. Glass is a widely used material in technical applications thanks to some of its unique properties: chemically inert, transparency to visible light, insulating properties at room temperature, high melting point, and one of the most abundant resource on earth, thus quite cheap. Nonetheless, its desirable properties play against it when it comes to laser welding. The low absorptivity, high chemical stability, and high melting points, unfortunately increase the complexity of the laser welding process in this material. Experiments have been conducted on 700 µm thin borosilicate glass plates (Mempax, Schott) for welding on silicon. The glass plates have a high surface quality with an arithmetic average roughness of 0.5 nm and a flatness of 2 µm. This surface quality is suitable to obtain local optical contact without external pressuring device. In this study, the welded seams were analyzed by a Raman spectrometer, using a frequency-doubled Nd:YAG (532 nm) laser source, to estimate the resulting residual stress. The results were extracted by the shift in position, the change in intensity and the variation of the width on the silicon peak at 520 cm-1. In nanosecond welding, melting of silicon can be observed, as well as the bonding of glass on silicon. In femtosecond welding, the absorption is more localized due to the non-linear process and clear mixing of the glass and silicon can be seen. The discrepancy regarding the temperature dynamics is presented to explain the different performances of the two techniques. The results clearly shown that the use of Femtosecond pulses preserve the material quality. Compared to the use of nanosecond pulses, there is lower residual stress, better homogeneity, and better transparency of the welded seams. Using femtosecond pulses, there is a strong bond with high mechanical resistance between the glass and the silicon. All the above results prove that the femtosecond pulses are better suited than nanosecond ones, for glass on silicon welding.

Resume : The family of materials known as diluted magnetic semiconductors (DMS) has received intense attention because of their potential in fields like optoelectronics and data storage. In DMS, a small fraction of the atoms in the lattice of a semiconductor is replaced by transition metal atoms such as Fe, Mn, Co or Ni. The low percentage of doping magnetic atoms allows to maintain the desirable electronic and optical semiconductor properties and at the same time incorporate magnetic response. Despite considerable progress, the mechanisms underlying DMS behaviour are still the subject of debate. Among the materials studied for DMS behaviour, the group of the II-VI semiconductors is particularly important. Zinc sulfide (ZnS) is of particular interest partly to a large bandgap which renders it particularly suitable for optoelectronics. In nanostructured form, ZnS shows appealing properties, and a broad range of morphologies have been synthesized. Among the dopants proposed for ZnS, Co is particularly favorable because the ionic radius of Co2+ is very close to that of Zn2+, which facilitates the inclusion of the transition metal ions in the semiconductor lattice with low strain. Pulsed laser deposition (PLD) is one of the preferred techniques to deposit high-quality thin films, often allowing stoichiometric transfer of multi-elemental targets to the substrates, together with fine control on the characteristics of the deposited film. When performed with ultrashort laser pulses, it allows the exploitation of complex irradiation schemes where energy deposition is controlled in the time scale of the laser-induced processes in the material. In the present work [1], a double pulse femtosecond irradiation approach was applied to a PLD experiment. With this methodology, we show here the double-pulse PLD fabrication of Co-doped ZnS crystalline nanoparticles. The analysis of the deposits morphology provides evidence on the effect of the double pulse irradiation scheme, indicative of a coupling effect on the material. TEM-EDX and Raman analysis revealed the crystalline nature of the nanoparticles, finding structures corresponding to the two polytypes of ZnS, wurtzite and zinc blende. The compositional analysis confirmed the presence of Co in individual crystalline nanoparticles. The influence of the interpulse delay on the composition was assessed, showing that the average Co/Zn ratio is lower than that expected from purely stoichiometric transfer. Neither this ratio nor its dispersion show changes as a function of the delay between pulses. [1] Ignacio Lopez-Quintas et al., Femtosecond Double-Pulse Laser Ablation and Deposition of Co-Doped ZnS Thin Films, Nanomaterials 10, 2229 (2020).

Resume : Fluoride and ZnO based materials occupy an original and strategic position in modern optics and optoelectronics. The fluorides exhibit unique optical features (low phonon energy, high transparency in UV region, suitable host for rare earth ion dopants), which make them excellent candidates for variety of optoelectronics and photonics applications. ZnO material can be utilized in several emerging applications in optoelectronics and sensors because of its properties, ie. good transparency, high electron mobility, and strong room-temperature luminescence. Combinations of these materials in nanostructured films might result in structures of interesting properties with a potential for application in optoelectronics. We demonstrate fabrication of either pure and Eu doped fluorides (CaF2 and LaF3), and pure and Eu doped ZnO nanostructured thin films by means of hybrid laser deposition technique. Pulsed Laser Deposition (PLD) utilizing pulsed Nd:YAG laser operated at 266 nm was used for fabrication of ZnO based material. Fluorides were prepared by Electron Beam Evaporation (EBE). We investigated dependence of morphology, optical and structural properties on mixture ratio of fluoride/ZnO content. Pulsed laser annealing (PLA) utilizing a KrF laser at λ=248 nm was performed to further modify these properties at fluence varied from 10 to 300 mJ/cm2. The effect of PLA on optical properties was characterized in-situ by spectrophotometry and photoluminescence measurements.

Resume : Carbon-based nanocomposites are meant to lead the electrochemical energy storage technology. In this work, we focus on the performance of graphene nanowalls (GNWs) mats grown on stainless-steel by chemical vapor deposition as electrodes for supercapacitor devices. In order to improve the GNWs intrinsic capacitance, we grew transition metal oxides nanoparticles (TMO NPs) on the graphene surface using an innovative optical technique based on pulsed laser radiation. For the electrode fabrication, the GNWs layers were laser processed immersed in several aqueous solutions containing organometallic salt precursors of Mn, Ce, Ni, Fe, Cu, and Co. Photothermal processes led to a substantial increase of the local temperature of the system allowing the crystallization of the TMO NPs on the surface of the GNW sheets with sizes of just few nanometers. The electrochemical performance of the electrodes was characterized using cyclic voltammetry, galvanostatic charge - discharge, and electrochemical impedance spectroscopy. The morphology and crystallographic nature of the phases were determined by means of transmission and scanning electron microscopies, besides Raman spectroscopy. The results showed exceptional augment of the electrodes capacitance with the incorporation of the TMO NPs: two orders of magnitude for positive electrodes, and three orders of magnitude for negative electrodes. Furthermore, it was demonstrated the functionality of the developed electrodes by manufacturing asymmetric supercapacitors using a PVA-H3PO4 solid electrolyte. The results showed that the devices maintain an areal capacitance of the order of that of individual electrodes, exhibiting excellent stability during tens of thousands of charge-discharge cycles, and retaining more than 95% of the initial capacitance and coulombic efficiency. The developed technique stands for a versatile, high throughput and easy way to fabricate hybrid graphene-based electrodes that only involves the use of non-toxic organometallic precursors as chemical reactive. The laser processing of the GNW materials was carried out with an industrial laser marking system, which allowed the reduction of the fabrication time, being this technique easily scalable to the industrial sector.

Resume : Ultra high precision machining of surfaces require gentle tools for high resolution, low-defect material removal at normal pressure that can be easily computer controlled. However, laser machining techniques still do not fulfill all requirements for such applications. Plasma processes enable high quality etching of various materials but require vacuum conditions. Laser and plasma processing are complementary technologies where each technology has its inherent advantages and shortcomings. In this presentation, a novel technology will be introduced which combines plasma and laser processing in order to make use of the advantages of both technologies. An ultra-short pulse laser source was used to generate a localized, free-standing micro plasma in a gas at atmospheric pressure by an optical breakdown. In order to modify, etch or deposit material, the plasma is brought in the proximity of a surface to allow the interaction of the species of the micro plasma with the surface. In particular, etching of fused silica and polyimide is discussed. These are reference materials etched by the laser-generated, reactive plasma that contains chemical species such as fluorine, chlorine or oxygen. In the presentation, the impact of selected parameters such as laser pulse energy, temperature, pressure, gas composition or plasma-surface distance on the etching rate and surface characteristics are shown. SEM, AFM, and XPS investigations reveal the achieved surface qualities and remarkable small chemical as well structural modifications.

Resume : Laser-induced (nano)ripples were found to enable reduction of (nano)fiber adhesion [1]. We demonstrated this with KrF* excimer laser irradiated poly(ethylene terephthalate) (PET) films, where nanoripples of different spatial periods were formed for variable angles of incidence. Similar structures were discovered on the so-called calamistrum located at the hindmost legs of cribellate spiders such as the garden center spider (Uloborus plumipes). These spiders produce nanofibrous silk to catch their prey; interestingly enough, the silk does not stick to the calamistrum which interacts with the nanofibers during silk production. The physical mechanism behind adhesion of the nanofibers to the prey is thought to be the van der Waals force. Therefore, for antiadhesion, the ripples are employed to decrease the contact area between the fibers and the base material, consequently reducing the van der Waals forces. Furthermore, the (nano)ripples might align the fibers to a certain extent, which could also contribute to a reduction of the adhesion. We characterized the laser-produced ripples by scanning electron microscopy (SEM), atomic force microscopy (AFM) and other techniques. In order to study their influence on adhesion we measured the deflection of spider silk and other fibers, when they had been brought into contact with gold-coated laser-processed and pristine surfaces. Furthermore, we investigated the influence of different environmental conditions and laser processing parameters. References: [1] Joel A.-C. et al., Biomimetic Combs as Antiadhesive Tools to Manipulate Nanofibers, Applied Nano Materials (2020) 3, 3395.

Resume : Thin film metallic glasses (TFMG) are considered valuable materials for niche markets in various domains such as biomedical, aeronautic and renewable energies. Their amorphous structure induces outstanding mechanical properties (Metal-like) and surface state (Glass-like). Ultrafast laser irradiation treatment can considerably increase the properties of the thin film coatings by creating multiscale surface structures named LIPSS (Laser Induced Periodic Surface Structures). Under controlled irradiation, TFMG undergo a remarkable self-organization process exhibiting very regular and homogeneous patterns with few bifurcations. The objective of this work is to explore the potential to create a multi-scale topography and to modify the surface physico-chemistry for the enhancement of the TFMG functionalities. Zirconium-Copper (Zr-Cu) thin film metallic glasses were irradiated by a femtosecond laser in order to structure the surface by tailoring multiscale patterns and topographical architectures. The initiation and the positive feedback leading to surface structuring are controlled by the femtosecond laser parameters (fluence and pulses number), allowing the formation of nanowells regularly disseminated. By using double pulses with delays between the pulses and controlled polarizations, HSFL (High Spatial Frequency LIPSS) were generated in addition to the nanowells. The concentration and uniformity of the latter can be regulated by modulating the temporal separation between the two pulses. These two types of nanostructures were analyzed by microstructural characterizations such as SEM, AFM and TEM, as well as statistical measurements. Those results obtained on binary alloys Zr-Cu propose irradiation strategies to achieve surface functionalization of TFMG improving physico-chemical features such as wettability, corrosion behavior or mechanical properties.

Resume : The possibility to fabricate nanostructured surfaces with tunable wettability is being extensively investigated both in research and industrial applications. Now, with the help of laser-based techniques, by combining surface architecture with surface chemistry it it possible to attain superhydrophobicity. In this paper we discuss our recent progres made in obtaining hydrophobic and superhydrophobic surfaces by matrix assisted pulsed laser evaporation (MAPLE). We will define the experimental conditions under which polymer films with tunable wettability can be obtained, the physical aspects, and some applications of the superhydrophobic surfaces obtained. First, we emphasize various polymer materials and advance the fabrication strategy adopted to fabricate superhydrophobic surfaces. In the following section we propose an explanation for tuning the wettability of the polymers surfaces and finally, we present a potential application and draw general conclusions along this proposed guideline for designing superhydrophobic polymer coatings by MAPLE.

Resume : Two Photon induced photopolymerization (TPP) is a very well-known microfabrication technique that allows the fabrication with many advantages such as 3D freeform fabrication due to its high degree of freedom. For many applications, especially in industrial use, a higher speed is desired for TPP fabrication. One possibility to speed up the fabrication is the use of parallelization optics, which could allow to decrease dramatically the TPP fabrication times. TPP parallelization requires the development of optical setups that accurately split the beam in order to fabricate with multiple beams. At the same time, all characteristics have to be maintained that make single beam TPP such an excellent fabrication technology. Furthermore, the photochemistry involved in the process must be also refined in order to increase the resin sensitivity, while minimizing the influence of each fabrication voxel on the neighbour photochemical reactions. In this presentation, a review of the approaches used for parallel TPP fabrication, as well as the different resins produced to such aim, developed within the frame of the European PHENOmenon project will be presented and discussed. The use of static and dynamic beam splitting will be introduced, discussing their advantages and drawbacks, proposing alternatives for the optimization of the technique for the parallel fabrication of complex 3D structures.

Resume : The high-field performance of resonator materials employed in state-of-the-art accelerators such as the large hadron collider or the European X-FEL strongly depends on e.g. impurity concentrations and surface flatness [1]. In particular, the applicable field gradient is limited by local defects with sharp morphologies like holes, pits, bumps, scratches or particles on the surfaces which lead to a reduced field emission threshold, an increased power loss or even a breakdown of a successful particle acceleration. Therefore, substantial efforts are invested to optimize the surface finish of the cavities. Conventional methods include mechanical grinding and polishing, buffered chemical polishing as well as electro polishing, however these techniques cannot quantitatively remove all relevant defects. Furthermore, the extensive use of chemical agents leaves non-negligible contaminations on the treated cavity surfaces, i.e. the cavities have to be carefully cleaned subsequently. As an alternative, metal surfaces can also be polished by employing short-pulsed lasers: Due to the interaction with intense laser radiation, the surface of the treated material is melted for a short time and the liquefied metal may solidify with smoothed surfaces under suited conditions. Additionally, the use of chemicals and related contaminations is thereby substantially reduced. Here, we have investigated the effect of laser treatments on rough niobium and copper metal surfaces. Different roughness profiles were prepared with standard emery papers and different polishing procedures. Surface regions of ca. 4 mm^2 were remelted by employing pulsed radiation from a Nd:YAG laser with about 10 ns pulse duration, 1064 nm wavelength, 7 mJ per pulse and scanning the laser beam over the area to be polished. The polishing procedure was controlled pulse-by-pulse by monitoring the electron emissions from the sample, as described elsewhere [2]. The morphologies of the so-treated metals were investigated by optical profilometry and scanning electron microscopy (SEM), and local electron field emission (FE) characteristics were measured using a FE scanning microscope [3]. The results show, that a successful polishing procedure critically and sensitively depends on the details of the laser illumination, such as the fluence and the number of laser pulses applied per surface area. The topography of the laser-treated metals prove the absence of sharp and jagged features as expected. FE experiments reveal a well-reproducible onset field for field emission after the laser treatment with reasonable field gradients for accelerator applications in contrast to conventionally polished materials. Future prospects of the technique will be discussed. References: [1] A. Gurevich, Supercond. Sci. Technol. 30, 034004 (2017). [2] V. Porshyn et al., J. Laser. Appl. 32, 042009 (2020). [3] P. Serbun et al., Rev. Sci. Instrum. 91, 083906 (2020).

Resume : In-situ boron doping of Ge can be of use in various types of devices. Ge:B layers can be employed as sources and drains in Ge pMOS transistors or as the p-type films in Ge p-i-n Photo-Detectors (PDs). If the growth temperature is low enough, they can even be used in GeSn PDs and Light Emitting Devices. Those SWIR and MIR devices are rapidly gaining interest since the demonstration of electrically pumped lasing, up to 100K, in GeSn stacks by the University of Arkansas. We recently obtained substitutional B concentrations up to 3.0x1020 cm-3 in high quality Ge:B layers grown at 349°C, 100 Torr with a fixed F(Ge2H6)/F(H2) = 7.92x10-4 Mass-Flow Ratio (MFR) and a F(B2H6)/F(Ge2H6) MFR varying from 0.0 up to 2.68x10-2. These substitutional concentrations were above the solid solubility limit of boron in Ge. Boron atoms then tend to form clusters, resulting in significant electrical deactivation. To assess material quality and try to improve the electrical activation of B in Ge (by dissolving those clusters), nanosecond laser annealing (NLA) experiments were thus performed on Ge:B / Ge:P / Ge SRB / Si(001) stacks in a SCREEN-LASSE tool, with energy densities (ED) ranging from 0.4 J cm-2 up to 2.0 J cm-2. The pulse duration was 160 ns +/- 2 ns and the laser wavelength 308 nm. The melt threshold was at 0.825 J cm-2, as determined by in-situ Time Resolved Reflectivity measurements at 638 nm. A detailed picture of the impact of NLA on Ge:B surface morphology, crystalline structure and electrical properties was obtained thanks to Atomic Force Microscopy, X-Ray Diffraction (XRD) and four points probe sheet resistivity measurements. Below an energy density of 0.825 J cm-2, surfaces remained smooth, with the same cross-hatch than for as-grown samples. At an energy density of 0.825 J cm-2 and above, isolated melted islands appeared. These islands multiplied as the energy density increased. For ED higher than 1.05 J cm-2, continuous liquid layers were formed. In this ED range, surfaces remained smooth. Single shot NLA experiments with ED higher than the melt threshold resulted in lesser quality structures, with a lower intensity of the Ge:B XRD peak and a higher sheet resistance than in as-grown layers. Multishot NLA experiments were thus performed. At first, the laser light was shone at the same position and with the same ED of 0.85 J cm-2 2, 10 and 100 times. As the shot count increased, isolated melted islands started to multiply, but no continuous layer was formed. Indeed, only part of the surface was melted. XRD profiles showed no changes compared to as-grown layers for less than 10 shots. For 10 or more shots, we had a complete loss of the Ge:B XRD shoulder peak. Next, we changed the energy density between 0.70 and 0.90 J cm-2 for 100 shots. Above the melt threshold, there was an increase of the melted islands size and a complete disappearance of the Ge:B XRD shoulder peak.

Resume : One of the most crucial challenge for optoelectronic and photovoltaic applications is the finding of a viable alternative to the use of transparent conductive oxide (TCO) and more especially to Indium based oxides (like the well-known and largely used Indium Tin Oxide). In recently published studies, we proved the possibility to obtain pure carbon transparent conductive electrodes thanks to an innovative full laser process while keeping high compatibility with standard microelectronic technology. We firstly elaborate Diamond-Like Carbon layers (DLC) by Pulsed Laser Deposition (PLD) of high purity graphite. This PLD grown DLC is a hydrogen and impurity free amorphous carbon composed of a homogenous mixture of sp² (graphitic) and sp3 (diamond) hybridized carbon atoms. It shares a strong kindship with diamond as being a perfect electrical insulator while presenting high transparency in the visible range. We demonstrate that performing UV laser annealing on DLC leads to bring high conductivity on its surface. This major change is explained by the formation of a fully graphitized sp² layer on the top of the DLC. Obtained conductivity and transparency is similar to commercial ITO performances. This technology presents some very innovative perspectives and interests. Annealed DLC layers are already suitable to be used as transparent resistors being able to dissipate high power without altering the layer. We also investigate the direct integration of this technology in an organic light emitting diode (OLED) showing the potential of this technology. We also highlight the biocompatibility of the layers, offering a very large application field to this technology.

Resume : Solid-state thin-film batteries are promising power sources for microelectronics. The thin-film cathodes in these batteries are annealed at about 600-700 °C to crystallize them into electrochemically active phases. This thermal treatment has several drawbacks such as uncontrollable loss of lithium, the need for thermally stable current collectors like Pt as a long processing time, which stimulates the search for more effective annealing approaches. Photonic based methods such as xenon flash lamp annealing (FLA), ultra-violet excimer laser irradiation (UV-laser), and pulsed infrared laser (IR) annealing can be employed for recrystallization of various thin-film materials. These methods employ light pulses that rapidly heat the surface and allow the crystallization of thin films in sub-second time while the underlying current collector and substrate remain unheated. In this work, we investigated FLA (millisecond pulses with broadband visible spectrum 200…1500 nm), UV-laser (20 ns pulses at 248 nm), and IR annealing (continuous wave mode at 1064 nm) for crystallization of two popular thin-film cathodes - LiMn2O4 (LMO) and LiCoO2 (LCO) and compared the three methods to the reference thermal annealing in terms of processing time, crystallinity, and electrochemical performance. FLA and UV excimer laser can crystallize LMO films on FTO sub-strates in short periods of 6 minutes and 25 minutes, respectively, compared to the thermal processing time of 60 minutes at 600 °C. The performance of the FLA-processed LMO cathodes (crystallinity, capacity, diffusion coefficient) is comparable to that of the thermal reference. LCO cathodes with thicknesses up to 3 µm could be crystallized by FLA. The rapid surface heating during FLA also offers a fast crystallization of thin-film cathodes on temperature-sensitive substrates. To demonstrate that, we crystallized LCO cathode films using FLA on aluminum foils. Flexible thin-film batteries consisting of an LCO cathode, lithium phosphorous oxynitride (LiPON) electrolyte, and Li metal anode were fabricated with a performance comparable to the best state-of-the-art thin-film batteries on rigid substrates.

Resume : The present work is focused on the realization of fully printed magnetic field sensors using a cost efficient commercially available material showing the magnetoresistive (MR) effect. The main challenge of this approach is the absence of the electrical conduction and MR-response of as-printed structures because particles of this material are easily oxidizing and are covered by organics directly after printing. To address this issue, we tested the functionalization of the printed material in air on the millisecond time scale using microoptically optimized diode laser array operating in the near infrared spectral range. The energy input on the millisecond time scale is desirable since such treatment simultaneously evaporates organics, enables particles sintering without their further oxidation and ensures the compatibility of the process with thermally sensitive substrates. For these experiments, the paste was formulated based on a commercially available material and sensor structures were screen-printed on various substrates ranging from rigid (alumina, glass) to flexible (polymer foils, paper) ones over inkjet or screen printed Ag electrical contacts. To realize electrically conductive structures revealing MR effect on different substrates, the optical power density and the dwell-time were varied in a broad range. Resulting sensors exhibit electrical resistances in the range of 100 Ohm, show isotropic sensitivity and MR effect typically up to 6% at 500 mT. In contrast to the laser processing, the conventional thermal treatment even in an inert gas mixture did not enable proper electrical conductivity and MR functionality.

Resume : Transparent conducting oxides (TCO) are important optoelectronic materials which are typically fabricated by sputtering techniques. Lately, many efforts have been devoted to the fabrication of TCO films by solution-based processes; however, they are still inferior in terms of opto-electrical perfor-mance, and often require high annealing temperatures. Among various TCO materials, indium-tin-oxide (ITO) is the most widely used for different optoelectronic applications such as displays, screens, solar cells, etc. because of its low electrical resistivity in conjunction with a high visible transmittance. Flash Light Annealing (FLA) is an attractive technique used for printed electronics, as the transient heating (1 μs - 10 ms pulse length) could be carried out on a temperature sensitive substrates without affecting them. However, as the emission spectrum of the Xenon lamps used in FLA has a max-imum in the visible region, it is difficult to process films that are optically transparent. In this work, we are proposing integration of an organic coloring agent onto ink-jet printed ITO films before application of the FLA. Because of the increased light absorption, a higher effective temperature can be achieved thus enabling effective sintering of the ITO films. As the result, uniform 250 nm thick ITO film with a sheet resistance below 150 Ω/□ and trans-mittance above 85% can be obtained with FLA. As-fabricated printed and annealed ITO films on glass were employed as transparent capacitive sensors, which can be used to unlock the LCD interface with the help of a touch-sensing mechanism.

Resume : CuO is one of the most widely studied p-type oxide semiconductor, thanks its peculiar properties, such as catalytic activity, high stability under gas exposure, antibacterial activity, optoelectronic properties. Therefore, CuO nanostructures (CuONs) find widespread applications in many fields: optoelectronics, solar energy cells, catalysis, energy storage and gas sensing. Anyway, the success of such technologies implies knowledge and control over the nanostructures’ properties (shape, sizes, structure and crystallinity) and consequently the development of simple, versatile, low-cost techniques for their production allowing such a fine control. To meet these requirements, we present a laser-based synthesis method for a controlled production of CuONs. In particular, by employing pulsed laser ablation in liquid environment, a simple, versatile and green technique, we have produced ligand-free CuONs with desired size, composition and shape. After a complete chemical (XPS, EDX, RBS, DSC, TGA), optical (UV-Vis, Raman), structural (XRD) and morphological characterization (SEM), we used CuONs to fabricate a chemoresistive gas sensor working at room temperature. Under Nitric Oxide (NO) gas exposure, CuONs-based sensor changes its resistance, showing good performances in sensitivity, selectivity, stability, low limit of detection and fast response/recovery time. In particular, at a temperature of 50°C, we found response and recovery times of 3 s and 21 s, respectively and a LOD of 2.28 ppm; good reproducibility of the tests after several days and good response in humidity conditions. The peculiar shape and size (20 nm thin needles) of CuONs obtained by the laser synthesis are promising for chemoresistive gas sensor.

Resume : Femtosecond laser sulfur hyperdoped silicon (fs-hSi) is capable of absorbing photons in the infrared spectral range while simultaneously exhibiting neglible reflection, thus representing a silicon-based material for infrared optoelectronic applications. For an effective generation and extraction photogenerated charge carriers have to diffuse from the depletion region to the metal-semiconductor-contact, before they recombine. However, laser processing of crystalline silicon creates detrimental amorphous and polycrystalline silicon surface layers due to high pressures occurring during rapid solidification of the material. Non-crystalline silicon phases exhibit a large density of recombination centers which reduce the effective charge carrier lifetime. Though crystalline silicon material is a prerequisite for electronically exploiting this material. Thermal annealing is a well-established approach to turn amorphous and polycrystalline phases into crystalline material again. This method restores the crystallinity successfully, but high annealing temperatures above 400 °C lead to a significant decrease in infrared absorption due to thermal diffusion of sulfur to silicon grain boundaries and sulfur cluster formation. The application of fs-hSi in an optoelectronic device requires an annealing process which restores the crystallinity and simultaneously supplies the infrared absorption of the sulfur dopants. This work demonstrates a two-step scanning femtosecond laser process, both performed with 100 fs laser pulses but with different fluences and atmospheres, for fabricating and annealing fs-hSi. The first process is carried out in sulfur hexafluoride atmosphere with high peak fluences resulting in laser-induced periodic surface structures and sulfur doping of silicon beyond the thermal saturation concentration. The following femtosecond laser process is used to heal the laser induced crystal damage and thus increases the crystallinity by processing with low laser peak fluence in vacuum atmosphere. The increase in silicon crystallinity is quantified by laterally probing the femtosecond laser annealed fs-hSi samples with Raman spectroscopy showing an increase in crystallinity of the lasered material. The optical properties like absorption are characterized up to a wavelength of 2500 µm with an integrating sphere. The resulting material, femtosecond-laser-annealed fs-hSi, shows to be a promising material for the application in infrared optoelectronic devices.

Resume : Understanding real structure-activity/selectivity correlations is a keystone in catalysis research for the development of tailored catalysts [1]. Pulsed Laser Post Processing (PLPP) has recently been applied as a promising tool to tune nanomaterials regarding e.g. optical and electro- chemical properties, phase composition, particle size, or defect density [2–5]. Therefore, applying PLPP allows implementing a correlational research agenda to individually study materials properties and catalytic performance of well-defined catalyst materials before and after PLPP. The recently published continuous liquid flat-jet setup for homogeneous excitation of colloidal particles by pulsed lasers [6] was deployed to modify Co- and Co-Fe-spinel nanoparticles. This led to improved catalytic activities which will be discussed in terms of laser-based modifications of the morphology and the material's defect density. Furthermore, the precise irradiation allows a systematic analysis and understanding of the underlying mechanisms for laser-based changes of materials properties on applying different laser parameters. [1] A.J. Medford et al. Journal of Catalysis 328 2015 36–42. [2] M. Lau, et al. ACS Appl. Energy Mater. 2018, 1, 10, 5366–5385. [3] M. Lau, Laser Fragmentation and Melting of Particles, Springer, Wiesbaden, 2016. [4] F. Waag, et al. Scientific reports 7 (1) 2017 13161. [5] D. Zhang, et al. ChemNanoMat 3 (8) 2017 512–533. [6] S. Zerebecki et al. J. Phys. Chem. A 2020, 124, 52, 11125–11132

Resume : Magnesium and its alloys are widely used due to their strength and low density. These properties make them very useful for many different structural applications where lightweight materials are required. In particular, they are excellent candidates as biomaterial for load-bearing degradable implants due to their excellent biocompatibility and biodegradability. However, their use is not widely generalized due to the excessive corrosion rate they experiment within corporal fluids, which compromises the mechanical integrity of the biomedical device in a too early stage. Different strategies have been studied to address this problem, but the problems of fast and localized corrosion remain unsolved. One promising surface modification technique to address the corrosion is the application of laser-textured patterns. In this work, we have explored the influence of different laser processing parameters (deposited energy, pulse length, etc.) on the degradation rate of magnesium alloys. Results suggest that with an adequate selection of the processing parameters the corrosion rate can be greatly reduced.

Resume : The suitable 3D printing approaches for piezo materials processing include Fused Deposition Modeling, Laser-based stereolithography (SLA), Digital Light Processing (DLP), Selective Laser Sintering, and Binder Jetting. Of the different additive manufacturing (AM) approaches, the SLA/DLP-based methods demonstrated the most promising results in terms of piezoceramics shaping due to high accuracy, reasonable dimensional control, and ability to use pastes and suspensions with high loadings (over 50 vol.%) of ceramic powders in the feedstock. In the present report, experimental studies were carried out to expose oligomers and measure the cured material to determine two key parameters related to the photopolymerization process: critical energy to initiate polymerization and penetration depth of curing light. The piezoceramic BaTiO3 material was observed for AM using a commercial SLA printer at 355 nm, a commercial DLP printer at 405 nm, and an experimental laboratory SLA setup at 465 nm. Working curves for the different photopolymers with piezoceramic filling degree showed unique behavior both within and among the resins as a function of curing light wavelength. The kinetic model of cure was proposed that could explain the critical energy to initiate polymerization and the penetration depth of curing light.

Resume : Flash lamp annealing is, like laser annealing, a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing: it allows the use of temperature-sensible substrates for thin films, leads to energy and cost savings compared to long-time annealing methods, and enables the formation of new materials in thermal non-equilibrium. Originally developed for microelectronics, flash lamp annealing has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, batteries etc. In this presentation, we shortly compare the pros and cons of flash lamp and laser annealing for thin film processing and discuss these issues at the example of thin semiconductor films on glass. In detail, the crystallization of amorphous Si on borosilicate glass, the crystallization of amorphous Ge on SiO2/Si substrates, and the formation of NiGe on different Ge substrates (amorphous, polycrystalline and monocrystalline) have been investigated. In all cases, the thin films were deposited by magnetron sputtering, followed by flash lamp annealing. The evolution of microstructure and its electrical properties was traced by corresponding characterization methods such as Raman spectroscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, sheet resistance and Hall effect measurements.

Resume : We applied femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for element detection with high spatial resolution and reconstructed chemical images from LIBS signals. Fs-lasers produce well defined ablation craters due to limited heat transfer out of the laser-matter interaction volume which is beneficial for high resolution LIBS imaging. In our experiments different lasers with a pulse length of 400 fs at wavelength 1040 nm and a length of 175 fs at 800 nm, respectively, were used. Laser pulses at the fundamental or the second harmonic wavelength were focused on the sample surface by glass lenses or a Schwarzschild microscope objective for plasma excitation. The specimens were placed on a 2D translation stage and measured applying one laser pulse per site on the sample surface. Investigated samples were (a) Cu grids (100 µm mesh) on Mn metal substrate, (b) Cu microdot arrays (dot size: e.g. 8 µm x 8 µm, thickness h = 60-300 nm) on Si wafers, (c) metal thin films (h = 35-500 nm for Cu, h = 5 nm for Ag) on glass slides, and (d) patterned metal oxide thin films on MgO crystals. Our results demonstrate accurate digital sample reconstruction from measured LIBS signal intensities for the Cu grid, the microdot samples and the metal oxide films [1]. For the Ag thin films the limit for optical detection was an ablated mass of 370 fg per pulse. For the Cu films the limit was 4.3 pg which is equivalent to a Cu particle of radius 490 nm. In further experiments we investigated orthogonal fs/fs double pulse (DP) LIBS to reheat the laser-induced plasma by a second fs-laser pulse in order to increase the optical plasma emission. We found out that orthogonal DP excitation enhances the emission line intensities in fs-LIBS (factor 2×) without reducing the spatial resolution of approx. 1.5 µm on Cu thin films. Acknowledgements: Financial support by the Austrian Research Promotion Agency FFG is gratefully acknowledged (K-project PSSP 871974). We thank M. Haslinger and Profactor GmbH for preparation of the Cu/Si samples. [1] C. M. Ahamer, K. M. Riepl, J. D. Pedarnig, Spectrochim. Acta Part B 136 (2017) 56-65. Doi:10.1016/j.sab.2017.08.005

Resume : Nanocomposite materials composed of plasmonic nanoparticles (NPs) inside semiconductor transparent thin films have recently attracted attention due to their unique physical and chemical properties. Particular interest represents laser-assisted fabrication and treatment of such materials, e.g. laser-induced self-organization of nanoparticles, structural modifications of the porous film, laser nanostructuring, etc. Here we demonstrate experimental and numerical results on the laser-assisted fabrication of plasmonic-semiconductor nanocomposites based on TiO2 thin films containing Ag and Au nanoparticles. The dependencies of the optical properties of such nanocomposites on laser irradiation parameters and on the metallic fractions are examined. The main mechanisms of Au and Ag nanoparticles formation in semiconductor thin film under UV laser irradiation, nanoparticle size distribution, composition and location are revealed and discussed based on the developed modeling. The obtained results pave the way for the application of laser techniques for a better-controlled fabrication of plasmonic-based thin films. The obtained nanocomposites can be used in novel nanophotonic devices for sensing, light field control as well as photocatalysis, photovoltaic, nonlinear optics and etc.

Resume : The properties of carbon-based nanocomposites can be tuned towards various applications by adding metals into the carbon matrix. Recently, we used a novel single-step laser-induced self-assembly process to produce hybrid materials composed of a carbon matrix and embedded gold-silver nanoparticles. SEM imaging revealed structures of well-controlled morphology including nanoparticles, 2D flakes, and 3D flowers ranging from micro- to nanometer sizes obtained by varying experimental parameters. Tunable parameters of the fabrication process are the laser irradiation time (CW, 325 nm, 10 – 60 min), the substrate (glass, polyethylene terephthalate, Al2O3 and Si wafers, Si nanowires), the concentration in liquid solution of the supramolecular complex ([Au13Ag12(C2Ph)20(PPh2(C6H4)3PPh2)3][PF6]5, up to 8 g/l), and the solvent (acetone, aniline, acetophenone or dichloroethane). Structural and elemental investigations of flakes by HIM, TEM, EDX, and XRD confirmed the presence of crystalline Au-Ag alloy nanoclusters (3 – 5 nm) in a crystalline orthorhombic carbon matrix. Optical characterization of flakes by photoluminescence and micro-Raman spectroscopy showed two emission peaks (with 457 nm laser excitation) and an induced modification with increasing laser power, respectively. Moreover, applications of these hybrid structures for surface-enhanced Raman scattering (SERS) induced by the plasmonic Au-Ag nanoparticles inclusions were demonstrated.

Resume : We report on the production of Ag nanoparticles (AgNPs) water solution, by means of a two-phase pulsed laser method, for the use in ophthalmological applications. The first phase of producing AgNPs > 20 nm consists in liquid laser ablation of a Ag target by using the fundamental wavelength (λ = 1064 nm) of a Nd:YAG laser. In the second phase we reduced the mean size of as-obtained AgNPs and also adjusted the size distribution by additionally irradiating with the 3rd and 4th ultraviolet harmonics (355 and 266 nm) of the same laser source. Our studies demonstrate that the most effective post-ablation treatment of initial colloids is represented by the consecutive irradiation with the 3rd and the 4th harmonics of the fundamental Nd:YAG laser wavelength. This way the synergistic effect between the two mechanisms of AgNPs light absorption was induced. Using this two-step approach we fabricated AgNPs contaminant-free colloids with a size < 10 nm and a narrow size distribution having a SD=±1.6 nm. Toxic effect on fungal and bacteria strains of the as-produced AgNPs was investigated. Considering the antimicrobial action, we therefore propose this procedure as a non-invasive method for ocular infections treatment and prevention

Resume : Samarium-cobalt (SmCo) is a permanent magnetic material having peculiar characteristics. Magnetic SmCo nanoparticles (SmCo Nps) can be used in different application fields such as sensors and biosensors for environmental and biological measurements and medical application, but little is known about their antimicrobial properties (1). SmCo Nps were produced using liquid phase Pulsed laser ablation technique (PLD) (2) and they were resuspended in Phosphate Buffer Saline (PBS). They were analyzed for their potential microbiological applications to cause the death of bacteria and viruses (3, 4). First of all, we evaluated SmCo Nps toxicity through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on Cellosaurus cell line Vero 76 after 24 hours. Nanoparticles resulted non toxic at any concentration tested. Our preliminary data are very encouraging: SmCo Nps in fact were active on Gram-positive bacteria to the highest concentrations, but they did not show any activity on Gram-negative bacteria, most likely due to the differences that they have in the structural composition. Furthermore, we also evaluated nanoparticles’ activity against Herpes Simples Virus Types 1 (HSV-1). SmCo Nps antiviral activity was assessed in co-exposure with the virus, inhibiting the viral replication during the early phases of infection at the highest concentrations. At the final, these preliminary data appear very interesting, emphasizing the innovative properties and applications of nanoparticles to act as antibacterial and antiviral agents. Our future aim is to extend the analysis towards microorganisms resistant to the common therapies, as well as verify SmCo Nps’s activity against the pandemic virus responsible of Coronavirus Disease 2019 (COVID-19). Bibliography: 1) J. Kudr, Y. Haddad , L. Richtera, Z. Heger, M. Cernak , V. Adam and O. Zitka. Magnetic Nanoparticles: From Design and Synthesis to Real World Applications, Nanomaterials, 2017. 2) Della Ventura B., Gelzo M., Dello Russo A., Edmondo B., Castaldo G., Gentile F.,Velotta R.. Novel and Sensitive Immunosensors Based on Metal-Enhanced Fluorescence by Nanostructured Surface:Application to Human IgG Detection in Urine (2018) 25° International Symposium On Matastable, Amorphous and Nanostructures Materials, Roma, 2/06/2018, 06/06/2018 3) D. V. Quy, N.M. Hieu, P Tra, N. H. Nam,N. H. Hai, N. T. Son, P. T. Nghia, N. T. V. Anh, T. T. Hong, and N H Luong. Synthesis of Silica-Coated Magnetic Nanoparticles and Application in the Detection of Pathogenic Viruses, Nanomaterials, 2013. 4) C. Xu, O. U. Akakuru, J. Zheng and A. Wu Applications of Iron Oxide-Based Magnetic Nanoparticles in the Diagnosis and Treatment of Bacterial Infections, frontiers in Bioengineering and Biotechnology, 2019.

Resume : Transition metal oxides (TMO) are a class of very interesting materials due to their optical, magnetic and catalytic properties. These properties are strongly related to oxides structure and morphology and a synthetic route that allows to control size and composition of obtained nanoparticles is essential. In last years, laser ablation in liquid (LAL) has been proposed as a simple technique to produce metal oxide nanoparticles without the use of any toxic reagents. However, nanomaterials obtained by LAL often present several phases and wide size distribution. The successive laser irradiation of the colloidal solution obtained by LAL can be a suitable strategy to overcome these drawbacks. We have ablated some transition metals (Fe, Mo, Ta and W) in water with femtosecond (800nm, 100fs, 1kHz) and nanosecond (532nm, 7ns, 10Hz) laser sources to obtain TMOs and we have studied the changes in their morphology and composition due to laser melting and fragmentation by irradiating colloidal solutions with a nanosecond laser. The obtained materials were characterized by microscopic, spectroscopic and diffractometric techniques.

Resume : Methods for laser processing of materials are evolving fast over the years as they provide unequaled spatial and temporal control, allowing to achieve transformations at interfaces on solids under air, controlled atmospheres or liquid environments. Those methods can trigger thermally activated physico-chemical phenomena which are not available with other alternatives involving high power consumption, long processing times, energy losses and incompatibility with thermally sensitive substrates. In this communication, we present a redox approach for the in situ synthesis of thin films on soda-lime-type glass substrates by means of a reactive variant of the Laser Induced Reverse Transfer (LIRT) technique. This alternative opens a new path to develop a plethora of electro-optic and sensor devices with features decisively more attractive from an industrial-scale perspective. In particular, we show that reactive LIRT can induce specific chemical transformations under ambient pressure. The latter are enabled with spatial control and at room temperature, providing facile selective modification of any transparent substrate surface. This research is supported by the project SPRINT (EU H2020-FETOPEN 801464).

Resume : When irradiated with a KrF* under an inclined angle, the laser-induces cones/spikes on polyimide foils can be used for directional fluid transport. The concept was inspired and abstracted from the European true bugs, which transport defense liquids on areas ornamented with oriented drop-like microstructures [1]. The fluid transportation occurs due to capillary action within the structured channels, and is strongly dependent on the microstructures’ curvature radii. A similar structuring pattern was used to ornament the lateral sides of microneedles. For manufacturing microneedle arrays, a two-photon polymerization (TPP) setup, with a fs laser was used. These microneedles were proven to transport a liquid film on their surfaces up to their tips, proving useful for biomedical applications where microneedles need to be coated with drugs/vaccines [2]. The TPP microneedle arrays can be used as replication masters, for mass production. References: [1] Hischen F. et al., The external scent efferent system of selected European true bugs (Heteroptera): a biomimetic inspiration for passive, unidirectional fluid transport, Journal of Royal Society Interface (2018) 15, 20170975. [2] Plamadeala C. et al., Bio-inspired microneedle design for efficient drug/vaccine coating, Biomedical Microdevices (2020) 22, 8.

Resume : Hybrid perovskite-silicon tandem solar cell architectures are currently considered as one of the more promising architectures for the widespread deployment of devices employing 2 junctions. These have the potential to go beyond the single junction Shockley-Queisser limit (ca. 33%). In fact, lab scale devices have already surpassed 29% efficiencies[1], already displacing the current record efficiencies for single junction silicon and perovskite devices. A range of strategies have been reported to interconnect the bottom silicon sub-cell with the top perovskite sub-cell [2, 3]. Forming a tunnel junction between the sub-cells is one such strategy. The connecting intermediate layer must efficiently transport one type of carrier from each sub-cell, whilst hindering the other carrier type. It must have a high vertical conductivity, but low lateral conductivity to prevent carrier recombination. Additionally, the optical coupling between the two sub-cells is critical to minimise parasitic absorption and unwanted reflectivity. Here we report on the current status of our approach[4] at forming tunnel junctions directly on the silicon sub-cell using GILD[5]. We believe that this approach is scalable, cost-effective, and simple to integrate into manufacturing lines, unlike tunnel junction formation by ion implantation [6]. In short, our doping system consists of an Nd:YAG ns pulsed 1064nm laser coupled to a high speed galvano head, which permits the rastering of the laser spot over areas up to 10x10 cm2. The wafer samples are held in an argon filled chamber at atmospheric pressure and saturated with phosphorus(V) oxychloride (POCl3). The laser pulse melts a thin (hundreds of nm) layer which quickly incorporates the phosphorus adsorbed at the surface of the wafer before solidifying. To form n /p tunnelling interfaces we used our system to n dope a thin layer on p emitters that were already formed on n-type silicon wafers. Laser pulse energy, spot spacing and pattern, and number of passages are varied and their impact on phosphorus n doping profiles is analysed by secondary-ion beam microscopy. Because the surface undergoes melting-solidification cycles, the resultant surface topology is analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). References 1 Green M, et al (2021) Solar cell efficiency tables (version 57). Prog Photovoltaics Res Appl 29:3?15. DOI:10.1002/pip.3371 2 Ko Y, et al (2020) Recent Progress in Interconnection Layer for Hybrid Photovoltaic Tandems. Adv Mater 32:2002196. DOI:10.1002/adma.202002196 3 Jo?t M, et al (2020) Monolithic Perovskite Tandem Solar Cells: A Review of the Present Status and Advanced Characterization Methods Toward 30% Efficiency. Adv Energy Mater 10:1904102. DOI:10.1002/aenm.201904102 4 Gaspar G, et al (2020) Sequential silicon surface melting and atmospheric pressure phosphorus doping for crystalline tunnel junction formation in silicon/perovskite tandem solar cells. In: 37th EU PVSEC 2020, European PV Solar Energy Conference and Exhibition, Lisbon. DOI:10.4229/EUPVSEC20202020-3BV.2.102 5 Turner GB, et al (1981) Solar cells made by laser-induced diffusion directly from phosphine gas. Appl Phys Lett 39:967?969. DOI:10.1063/1.92628 6 Bellanger P, et al (2018) Silicon Tunnel Junctions Produced by Ion Implantation and Diffusion Processes for Tandem Solar Cells. IEEE J Photovoltaics 8:1436?1442. DOI:10.1109/JPHOTOV.2018.2864632 Acknowledgements: This work was supported by national funds FCT/MCTES (PIDDAC) through the grant agreement PTDC/CTMCTM/28962/2017.

Resume : We present a study on the formation of Laser Induced Periodic Surface Structures (LIPSS), with linearly polarized femtosecond UV laser pulses (265nm), on the surface of free-standing films of Poly(ethylene terephthalate) (PTT) and PTT reinforced with tungsten disulfide nanotubes (PTT-WS2) and their effect on the chemical and mechanical properties of both materials. We report the changes in the surface topography, wettability and surface energy, Young Modulus and adhesion force, by means of Atomic Force Microscopy, contact angle and Peak-Force Quantitative Nanomapping measurements, respectively. LIPSS were formed at 15.9-31.3mJ/cm2 for PTT, and at 19.1-33.9mJ/cm2 for PTTWS2 for 500 to 10000 pulses. We attribute the higher fluence needed for their formation in PTT-WS2 to its higher crystallinity and heat diffusion. LIPSS formed parallel to the laser polarization with a period close to the wavelength of the laser. The effect of nanostructuring was similar in both materials: the original samples were hydrophilic, which increased after irradiation; little change was found in their total surface energy, but their negative polar component increased radically; and LIPSS formation did not affect the Young Modulus, although a decrease by a factor of four was found for the adhesion force. We conclude that the origin of this behavior as well as the increase of negative polar surface energy is a change of surface chemistry during irradiation.

Resume : There is increasing interest in laser-induced formation of 3D porous graphene-like carbon electrodes and sensors from polyimide under ambient conditions. This agile method offers the potential of tuning the hierarchical porous structure and the degree of order through varying laser parameters (power, scan speed). In turn, these structural and electronic properties can have a significant influence on the performance of these carbon nanomaterials for sensing applications, such as humidity sensing. Traditional “One-Factor-At-a-Time” (OFAT) optimization approaches are limited since they do not take account of interaction effects between design parameters (in this case laser power and scan speed). Here we report on a Design of Experiments methodology for rapid optimization of the formation process for laser-induced porous 3D graphene-like carbon (LIG) via a Design of Experiments methodology with a low-cost CO2 laser engraving tool. This methodology (taking sheet resistance as the parameter to be optimised) allows us to produce LIG structures with graphene-like Raman signatures, ie full-width at half-max of the 2D peak ~60-80 wavenumbers (cm-1). Interestingly, the Design of Experiments methodology reveals parameter combinations that yield comparable Raman data while reducing write time by a factor of 5 for only a modest increase in sheet resistance (from 16 ohm/sq to 36 ohm/sq). Proof-of-concept humidity sensors fabricated using this DoE approach yielded order of magnitude increases in device capacitance (~0.8 pF to ~10 pF) for a relative humidity of 80% vs 0%. These data highlight the opportunities for efficient optimization of these nanoscale materials for development of direct-write, low-cost sensing elements.

Resume : Additive manufactured (AM) materials with gradually changing composition, so-called Nabla-materials, promise a revolution in industrial applications. The materials' properties such as flexibility, abrasiveness or density can be varied in the same part. One method to prepare functionally-graded additively manufactured materials (FGAM) is direct metal deposition as (a mixture of) metal powder injected into a gas jet and coaxially directed onto a cw-laser generated meltpool at the workpiece’s surface. By functionally grading the chemical composition and hence the physical properties of a workpiece, AM enables unprecedented opportunities in automotive, aerospace and medical applications, where engineers direct their close attention to a high standard combination of quality assurance and quality control (QA/QC) [1]. Laser-induced breakdown spectroscopy (LIBS) is a fast and cheap method to do elemental analysis, as it requires no sample preparation and only optical access to the parts during the graded manufacturing process [2]. For additively manufactured goods, LIBS as a fast, sensitive and micro-invasive method does not interfere with the laser-based AM process and represents the only method to access chemical information of the solidified solder after each addition in real time [3]. This information is neither accessible after the completed AM process, nore via slow and insensitive x-ray spectroscopic methods during the AM buildup. We present our latest results using LIBS on AM-parts. [1] https://doi.org/10.1016/j.addma.2018.06.023 [2] https://doi.org/10.1364/OE.27.004612 [3] https://doi.org/10.1016/j.addma.2018.10.043

Resume : The performance of transparent silver nanowire (AgNW) electrodes can be improved by using thin coatings of two-dimensional assemblies of amino-terminal oligoglycine (denoted as tectomers), which causes a 50% sheet resistance decrease for AgNW electrodes with initial resistivities of 100 Ω/sq, while largely retaining the electrodes’ high transparency. Tectomer coatings also remarkably impart enhanced hydrophobicity and protection against AgNW degradation under ambient conditions. Additionally, these coatings are pH-sensitive, and their rich surface chemistry enables opening new perspectives on the fabrication of AgNW electrodes with (bio)sensor functionalities.[1] In this work, we report on the laser patterning of AgNW electrodes biofunctionalized with tectomer coatings. A pulsed, green laser (532nm) was utilized to create non-conductive paths, 12 to 50 µm in width (Figure 1), and the conditions were tuned to avoid the damage of the substrate materials: glass and polyethylene terephthalate (PET) for rigid and flexible electrodes, respectively. The electron transport properties, transparency, and durability of the resulting interdigitated electrodes were characterized, and their potential applications in optoelectronics will be discussed. 1. Jurewicz, I., Garriga, R., Large, M. J., Burn, J., Bardi, N., King, A. A. K., Velliou, E. G., Watts, J. F., Hinder, S. J., Muñoz, E., Dalton, A. B. Functionalization of silver nanowire transparent electrodes with self-assembled 2-dimensional tectomer nanosheets. ACS Applied Nano Materials, 1(8), 3903-3912. 2. Seral-Ascaso, A. et al., submitted.

Resume : Rising worldwide energy-consumption and burning of already depleting fossil-fuel reserves drive the climate change. Simultaneously, fabrication techniques of the eco-friendly devices often demand handcrafted, complicated procedures that are not always scalable to the commercial level. Therefore, emphasizing the versatility and scalability of the synthesis procedures for the new technologies becomes increasingly important to facilitate change towards “green” energy sources. The laser-assisted modification approach meets the selected criteria, thus combining it with a flexible substrate creates a potential for a variety of applications. One of such materials would be titania, in the form of laterally-spaced nanotubes grown on the elastic foil. Here, we propose the usage of the laser for selective closing of the titania nanotubes. Irradiation with a 355 nm pulsed laser at 30 mJ/cm2 allows a formation of a tight seal over the nanotube opening, trapping the molecules deposited inside or on the formed cap.[1] Due to the innate biocompatibility and corrosion resistance of the titania, the presented system can be used in research involving living cells or even in vivo. On the other hand, since the titania exhibits photoactive properties and the nanotubes effectively multiply the available surface area, the development of a TiO2-based photocatalyst is feasible. Sputtering a thin metal oxide layer over the nanotubes prior to the laser treatment leads to the formation of the defect-rich, semi-crystalline electrode after irradiation with the same laser at 50 mJ/cm2. In the oxygen evolution reaction, the electrode prepared in such a way exhibits approximately 240 times higher current densities (compared to the bare nanotubes), which are boosted by an additional 15% under solar radiation.[2] In summary, we demonstrate laser-assisted modification technique that utilize geometric transformation of the titania nanotubes, as well as a simple modification with a metal oxide layer resulting in a creation of an efficient, photoactive electrode for oxygen generation. The employed materials and techniques are highly-scalable and easily adjustable, generating a minimal amount of waste throughout the modification process. This work was supported by the Polish National Science Centre. Grant Number: 2017/26/E/ST5/00416. 1. Wawrzyniak, J.; Karczewski, J.; Kupracz, P.; Grochowska, K.; Coy, E.; Mazikowski, A.; Ryl, J.; Siuzdak, K. Formation of the Hollow Nanopillar Arrays through the Laser-Induced Transformation of TiO2 Nanotubes. Sci Rep 2020, 10, 20235, doi:10.1038/s41598-020-77309-2. 2. Wawrzyniak, J.; Karczewski, J.; Coy, E.; Iatsunskyi, I.; Ryl, J.; Gazda, M.; Grochowska, K.; Siuzdak, K. Spectacular Oxygen Evolution Reaction Enhancement through Laser Processing of the Nickel‐Decorated Titania Nanotubes. Adv. Mater. Interfaces 2021, 8, 2001420, doi:10.1002/admi.202001420.

Resume : Due to their superior electro-optical properties, liquid crystals (LCs) have a long tradition of being used to dynamically change the properties of light. Some of the most famous applications of LCs are spatial light modulators or flat-panel displays. Additionally, LCs have also been used for integrated photonic circuits to alter the refractive index of planar waveguides i.e. in combination with glass, silicon, or polymers. A waveguide type, which has so far not been combined with the technology of LCs, are the so-called femtosecond laser direct written waveguides. This waveguide type is created by modifying the volume of a transparent material using femtosecond laser pulses. In the past decades, this fabrication technology has advanced from first proof of principle demonstrations to a well-recognized method for fabricating photonic devices in various glasses. However, one of the biggest drawbacks of this technology is the limited possibility to actively tune, switch or reconfigure the devices once they are fabricated. Up to now, most approaches to tune the device properties actively are based on thermal effects. We present a novel approach of fabricating switchable femtosecond laser direct written devices by using LCs. For this, femtosecond laser direct written waveguides have been added to a liquid crystal cell to demonstrate the potential of using liquid crystals for tuneable waveplates in integrated photonic circuits. A commercially available empty liquid crystal cell (LCC1318-A, Thorlabs) is used as the sample for the experiments. The liquid crystal cell consists of two fused silica substrates coated with indium tin oxide (ITO) and polyimide (PI). The ITO-layers are used as electrodes for the cell, whilst the PI-layers are the anti-parallel alignment layers for the LCs. The glass substrates are glued together by a mixture of glue and spacers, which is applied to the rim of the cell. The gap between the substrates is 8µm. We polished the top side of the cell to enable transversal inscription of waveguides with a femtosecond laser (a longitudinal inscription was not feasible due to the damage the laser beam can induce in the ITO and the alignment layer of the cell). The laser beam is reshaped using an anamorphic zoom system to enable low birefringence waveguides. Laser pulses are focused using a 20x objective lens (NA=0.42, Mitutoyo) mounted on a z-stage (Aerotech ANT130-060-L). Waveguides are inscribed into the liquid crystal cell using laser pulses at 100 kHz repetition rate and 515 nm wavelength. The pulse duration is set to 300fs. The waveguides were interrupted by a 0.1mm gap around the liquid crystal interface to avoid damaging the ITO and PI layers. We show that it is possible to use liquid crystal cells as switchable retardation elements in femtosecond laser direct written circuits. The retardation inside the waveguide can be changed using the applied voltage, allowing e.g. to switch from anti-diagonal to diagonal output polarization.

Resume : Direct Laser Interference Patterning (DLIP) with ultrashort laser pulses (ULP) represents a precise and fast technique to produce tailored periodic sub-micrometer structures on various materials. In this work, an experimental and theoretical approach is presented to investigate the previously unexplored fundamental mechanisms for the formation of unprecedented laser-induced topographies on stainless steel following proper combinations of DLIP with ULP. The combined spatial and temporal shaping of the pulse increases the level of control over the structure features whilst it brings new insights in the structure formation process. DLIP is aimed to determine the initial conditions of the laser-matter interaction by defining an ablated region while double ULP are used to control the reorganisation of the self-assembled laser induced sub-micrometer sized structures by exploiting the interplay of different absorption and excitation levels coupled with the melt hydrodynamics induced by the first of the double pulses. A multiscale physical model has been developed to correlate the interference period, polarization orientation and number of incident pulses with the induced morphologies. Special emphasis is given to electron excitation, relaxation processes and hydrodynamical effects that are crucial to the production of complex morphologies. Results are expected to derive new knowledge of laser-matter interaction in combined DLIP and ULP conditions and enable enhanced fabrication capabilities of complex hierarchical sub-micrometer sized structures for a variety of applications.

Resume : The creation of effective nanoscale sources of broadband (white) radiation, operating in the visible range, is an essential task for the development of active elements of nanophotonics, ultra-compact optical chips, and the study of biological objects. Metal-dielectric nanostructures, combining the plasmon and dielectric components, provide a high degree of localization of electromagnetic energy (plasmon component) and low optical losses (dielectric component), as well as strong nonlinear optical properties. Here we study ultrathin gold films at silicon films or bulk after exposure by femtosecond laser pulses resulted in the integration of metal and high-index semiconductor components. Obtained structures demonstrate a broadband response under excitation with femtosecond pulses at 1050 nm as well as a strong second harmonic generation.

Resume : In highly porous carbon electrodes, a large fraction of pores is inaccessible to the electrolyte, which reduces the capacitance. This effect is accentuated at high charge/discharge current densities (> 1 A/g). Creating additional channels in the porous electrode has been shown to overcome this limitation by promoting a four-fold increase in the specific capacitance at ca. 25 A/g [1]. Ion diffusion can be monitored through Probe Beam Deflection (PBD) [2]. In short, this technique allows the detection of mass flows in the electrolyte diffusion layer due to changes in the concentration gradients (and hence the refractive index) within a 100 ?m distance from the electrode surface. In this particular case, the beam initially travels parallel to the electrode/electrolyte interface and its rate of deflection towards or away from the interface is dictated by the variation of the ionic concentration. This work reports on how device performance and ionic diffusion are altered when porous carbon-based electrodes are modified by opening up vertical channels. The screen-printed electrodes were modified using a 1064 nm Nd:YAG pulsed laser (spot diameter ca.42 ?m). Changing the pattern and the laser rastering speed allowed to tune the distance between consecutive channels whilst their diameter and depth was varied by applying different pulse energies. Moreover, two different electrode thicknesses were tested (ca. 140 ?m and ca. 200 ?m). These features were then inspected via profilometry measurements. Complementarily to PBD, cyclic voltammetry and galvanostatic charge/discharge measurements were undertaken to evaluate performance metrics dependence on electrode modification. [1] J.Y. Hwang et al. Adv. Funct. Mater. 27 (2017) 1605745 [2] F. Decker et al. J. Electroanal. Chem. Interf. Electrochem. 228 (1987) 481-486 Acknowledgements: This work was supported by national funds FCT/MCTES through the grant agreement UIDB/50019/2020 – IDL – Instituto Dom Luiz.

Resume : The fabrication of diffractive elements in ophthalmic polymers to induce refractive index changes to be applied for refractive correction is of great interest in the field of Optics and Ophthalmology. In this work, silicone hydrogel used for soft contact lenses were structured with linear periodic patterns by means of Direct Laser Interference Patterning (DLIP). As laser sources, a Q-switched laser system emitting 10 ns pulses at a wavelength of 266 nm and a mode-locked solid-state oscillator delivering 12 ps laser pulses at a wavelength of 532 nm were used to produce periodic patterns on the surface of the polymer material. DLIP structuring was carried out employing a two-beam interference setup, studying the features of the laser processed areas as a function of both the laser fluence and the interference period. Next, static water contact angle (WCA) measurements were carried out with deionized water droplets on the structured areas. Contact angle variation was evaluated as a function of time to study the hydration properties of DLIP structures. The topography of the structured areas was investigated using optical confocal microscopy. Compositional and structural modifications on the materials were studied by means of micro-Raman spectroscopy. Finally, periodic patterns were characterized through diffractive techniques to determine the diffractive properties of the DLIP periodic patterns.

Resume : Laser marking is a well-established advanced technology for locally modifying object properties or for producing robust object identification at the micrometer scale such as with QR Codes or color marking. Color laser marking consists in focusing a high-power laser onto a metal material surface. The focused spot acts as a local heat source, leading to the formation of an oxide layer in the case of color marking. When illuminated, the incident light is reflected from the upper and lower interfaces of the oxide layer, leading to interference and the appearance of a color which depends upon the thickness and refractive index of the layer. These properties depend themselves on the temperature to which the metal is heated. The spectral response and subsequent color information of the laser-induced colored sample is generally measured using a standard spectrometer or ellipsometer. Due to their design, these instruments only provide a global spectral response over an area of a few thousand µm². However, color laser marking is a local process that modifies the metal structure at a scale of micrometers, dependent on the size of the focused laser spot. Consequently, the spectral analysis would be more accurate locally if carried out at the micrometer scale, allowing the exploration of local information of the thin films. In this work, we propose to extract both the 3D topography and the 2D spectral color response of laser-induced colored samples at a scale of around 1 µm in only one measurement and without the use of an external spectrometer or ellipsometer. The technique proposed is to use low coherence interference microscopy and to apply a Fourier-transform analysis to the polychromatic fringe signal to produce a dual quantitative spectral/topographical response at each pixel in the field of view covered by the acquired image size. To achieve this, a careful system calibration is required. The technique benefits from the classical advantages of white light interference microscopy, i.e., contactless imaging over a large field of view with a lateral resolution limited by the diffraction of light (about 1 µm). Experimental results on multiple laser-induced colored stainless steel samples were obtained using an original home-built white light interference microscope in the Linnik configuration. The results demonstrate the ability to extract the spectral information and subsequently a color map of the sample showing color variations at a scale of around 1 µm. By providing clear identification of micro-sized areas of color difference, this characterization tool has potential to better monitor the color process parameters.

Resume : Current challenges in printed circuit board (PCB) assembly and IC packaging technology involve high resolution for ultra-fine pitch components (< 0.3 mm and < 60 ?m respectively), high throughput and compatibility with flexible substrates. These challenges are poorly met by the conventional deposition techniques (e.g. slot die coating and stencil printing), thus the need for a digital and high-resolution deposition technology is essential. Laser-Induced Forward Transfer (LIFT) constitutes an excellent alternative for assembly and packaging of electronic components: it is fully compatible with the widely used soldering materials, it is environmentally friendly and offers versatile control over the printed solder paste volume with high resolution (< 50 ?m) and throughput (up to 10000 pads/s). In this work, a novel process for printing lead-free, jettable solder paste (powder size 15-25 ?m; metal loading 87%) relying on LIFT is reported. A side-view imaging configuration is employed by coupling a LIFT setup with a high-speed camera for the real-time visualization of the ejection process. The experimental data from the captured videos are analyzed to determine morphological aspects, such as the volume of the printed pattern. Transfers are achieved with diameters ranging from 50 to 150 ?m and printed volumes down to sub-nl. Finally, the reported process is applied for the actual assembly of a 0.22 mm ultra-fine pitch BGA IC on FR4 type PCBs, resulting in functional demonstrators.