Nanomaterials- electronics & -photonics

Resume : Upconversion of sub-band-gap photons is a promising technique for improving the efficiency of silicon-based solar cells beyond the Shockley-Queisser limit. Trivalent Erbium ions are well suited for upconversion from 1500 nm to 980 nm, but their small absorption cross section limits the efficiency. Topology optimization of gold nanostructures can be used to enhance the efficiency and the optimized nanostructure geometry can be produced using electron beam lithography. The talk will introduce a simple rate-equation model for upconversion and discuss how topology optimization is used to design gold nanostructures to optimize the amount of upconverted light. Numerical and experimental results will be presented.

Resume : In this work, Mie resonances in single Si nanoparticles (NPs) of different sizes have been systematically studied, using dark field (DF) and cathodoluminescence (CL) spectroscopy. An analytical method has been developed to compare experiment with theory. Experimental CL spectra are averaged over entire Si NPs, allowing for direct comparison to DF spectra of identical NPs. Theoretical spectra clarify the assignment of Mie resonances within the NP which contribute with different intensity in DF and CL, resulting in an apparent spectral shift. Furthermore, a substrate effect appears. A 100 nm-Si NP on 15 nm SiN results in a broad peak, spectrally in between that of the calculated electric and magnetic dipole, a NP on 50 nm SiN exhibits two separated peaks as theoretically predicted. High spatial resolution of electron beam excitation allows to study the spectral CL changes at varying beam impact parameters. Theory and experiment agree that depending on beam position within a small Si NP, relative intensity of electric and magnetic dipole change; electric dipole vanishing in the center of the NP. Similar results are found for larger (d = 210 nm) Si NPs although the mode assignment is challenging as higher order modes appear and overlap with others. In conclusion, comparison of CL and DF spectra is not trivial, in fact, excitation/radiation of distinct Mie resonances within a single Si NP are dependent on beam placement. However, substrate effects need to be considered in CL.

Resume : Due to their unique ability to con ne light to the nanoscale, plasmonic nanoparticles are the topic of investigation in photovoltaics, nano-sensors, drug delivery, and nano-optics. Furthermore, the optical response of these materials can be tuned and optimized for different applications by controlling the shape, size, and configuration of nanoparticle assemblies. In this regard, the modelling of nanoparticles plays a significant role in obtaining optimized nanostructures. To predict the optical response and to support experimental results of regular self-assembled plasmonic nanoparticle supper-lattices, we modelled different combinations and geometric parameters of nanoparticle clusters using the finite element method (FEM). The FEM simulations show a strong increase in the degrees of freedom with increasing particles per cluster, which enormously increases computational time, making optimization routines impossible for a large cluster of nanoparticles. Nevertheless, the optical response of particle clusters shows that the plasmonic modes arise from the single-particle mode, coupling modes, and the cluster lattice etc. Here, we present a statistical approach to predicting the plasmonic response of a sample. Scanning electron microscope (SEM) image processing of self-assembled nanoparticles gives the statistical information of cluster morphologies and distribution on the substrate. Based on the image processing input, we optimize linear combinations of FEM models to predict the whole sample's optical response. We support and verify our results by the experimental extinction curves of self-assembled nanoparticle samples. Our results indicate the potential of predicting the plasmonic effect of the large-scale particle cluster arrangements from the response of single, varying clusters.

Resume : We study the assembly kinetics of surfactant-stabilized gold nanoparticles in the presence of sulfate ions. The reaction proceeds in two steps: very rapid (a few minutes) formation of amorphous aggregates, followed by slow reordering (over several hours). The latter process is the only one detectable via absorbance spectroscopy and results in the formation of intimate contacts between the objects, with interparticle distances below the thickness of a surfactant bilayer. The rate-limiting step of the reaction could be related to surfactant expulsion from the initial aggregates, which allows the particles to come in close contact and form chains. There are marked differences in reaction yield and rate constant between spheres, rods and bipyramids, highlighting the role of surface curvature in contact formation. Once formed, the assemblies are very sturdy and stable under centrifugation and dialysis. The contact interaction is strong and highly directional, as shown by liquid-cell transmission electron microscopy.

Resume : Cluster-assembled metallic films show interesting electrical properties, both in the near-to-percolation regime, when deposited clusters do not form a complete layer yet, and when the film thickness is well above the electrical percolation threshold. Correctly estimating their electrical conductivity is crucial, but, particularly for the latter regime, standard theoretical tools are not quite adequate. We therefore developed a procedure based on an atomically informed mesoscopic model in which ab-initio estimates of electronic transport at the nanoscale are used to reconstruct the conductivity of molecular dynamics simulated films of tens of clusters using an effective resistor network that appropriately accounts for ballistic transport. The method is shown to correctly capture one of the signature features of such systems, the non-monotonic behaviour of the conductivity as a function of the film thickness.

Resume : Hysteresis is a limiting factor for the actuation accuracy of PbZr1-xTixO3 (PZT) ceramics and thin films. Explanation of hysteresis for these materials using phenomenological models such as Rayleigh model is a common practice. On the other hand, application of Rayleigh model and its variants results in significant discrepancies in explaining the hysteresis behavior in epitaxial thin films. Here, hysteresis in application-relevant, epitaxial, monoclinic PbZr0.55Ti0.45O3 films were investigated for non-switching AC excitation fields at zero and 20 kVcm-1 DC bias cases. The hysteresis, loss and nonlinearity in the strain and polarization response of the films show unique features that is not expected from the Rayleigh model. The strain exhibits a hysteretic behavior and is linear with the excitation amplitude. However, the polarization is hysteretic and highly nonlinear over the investigated frequency range from 70 Hz to 5 kHz. The application of the bias shows almost no change for the strain response, whereas the loss tangent and nonlinearity of the polarization are significantly reduced. The observations are explained by a new model, the so called polarization rotation model. This model describes the film properties as a result of the nonlinear rotation of the polarization vector within the monoclinic unit cell in response to the applied electric field, accompanied by a viscous interaction of the domains. The model can describe the scaling of the loss tangent and (non)linearity of the strain and polarization in an amplitude and frequency range that is far exceeding the applicable range of the Rayleigh model. It is shown that the nonlinear response and the hysteretic loss can be ascribed to two separate processes. The nonlinearity stems from the nonlinear nature of the rotation of the polarization vector. On the other hand, the hysteresis and ferroelectric loss stems from viscous interactions of domains during the rotation of the polarization vector. [1] Lucke, P., Bayraktar, M., Birkhölzer, Y. A., Nematollahi, M., Yakshin, A., Rijnders, G., . . . Houwman, E. P. (2020). Hysteresis, Loss and Nonlinearity in Epitaxial PbZr0.55Ti0.45O3 Films: A Polarization Rotation Model. Advanced Functional Materials, 30(52), 2005397. doi:https://doi.org/10.1002/adfm.202005397 [2] Lucke, P., Bayraktar, M., Schukkink, N., Yakshin, A. E., Rijnders, G., Bijkerk, F., & Houwman, E. P. Influence of DC Bias on the Hysteresis, Loss, and Nonlinearity of Epitaxial PbZr0.55Ti0.45O3 Films. Advanced Electronic Materials, 2100115. doi:https://doi.org/10.1002/aelm.202100115

Resume : Luminescent materials based on RE-activated vanadates are widely used for various science and technology purposes because the vanadates are characterized by high optical absorption in a wide spectral range, effective energy transfer from the hosts to activator RE ions, and by intensive emission. Within our previous research we have found conditions of synthesis those allowed to achieve high intensity of luminescence emission of the RE-doped vanadate nanoparticles synthesized by sol-gel method. The next important task is to save high optical characteristics of oxide nanoparticles at their deposition on various substrates. It is important to prevent loses of luminescent characteristics of nanoparticles with their incorporation in films and various coatings. One of the perspective ways to save luminescent properties of the applied nanoparticles is pulsed laser deposition (PLD), because this method doesn?t require nor any matrices for dispersion of nanorarticles like a polymeric (silicon) matrix for the YAG:Ce particles used in WLEDs, neither heavy metal or organic solvents as in liquid phase epitaxy method. In the work we report results of experiments with pulsed laser deposition (PLD) of the RE-activated lanthanum vanadate nanoparticles on glass and silicon substrates. The applied vanadate nanoparticles were synthesized by aqueous nitrate-citrate sol-gel method using citric acid as a complexion agent. The deposition of nanoparticles was carried out using KrF excimer laser with ?gen = 248 nm. Peculiarities of the PLD process of the vanadates was reported previously very shortly and mainly for yttrium and neodymium vanadates. Therefore, various experimental attempts were carried out in order to find optimal experimental conditions such as pulse power, repetition rate, and deposition duration. The conclusion was made about favorable conditions for pulsed laser deposition of vanadate nanoparticles on glass and silicon substrates. Morphology and spectral properties of the obtained samples were investigated. It was found that nanoparticles forming the films have morphology (shapes and sizes of nanoparticles and their agglomerates) similar to those in free powders. Luminescent properties of the films are also similar to ones observed for the nanoparticles before deposition. Thus, the applied method of deposition allowed us to safe properties of nanoparticles in the composite films.

Resume : We propose a method for predicting the Chemical Vapor Deposition (CVD) epitaxial growth of SiGe-based structures, using an extension of the open-source “MulSKiPS” code developed by our group and demonstrated for the Physical Vapor Deposition (PVD) epitaxy of 3C-SiC. MulSKiPS is a Kinetic Monte Carlo super-Lattice (KMCsL) code, designed to study at atomic resolution the growth kinetics of materials with sp3 bond symmetry. Its super-lattice nature makes the code unique within Lattice KMC codes. The evolution of point-like and extended defects can be predicted as a function of the initial substrate condition, without labelling the substrate lattice points. In addition, the morphology evolution during growth/etching processes - e.g. of flat, structured, or patterned substrates, or nanoparticles – can be simulated, correlating morphology and defect kinetics. The ensemble of chemical reactions occurring in the vapor phase or at the solid-vapor phase boundary is effectively accounted for by the absorption/desorption and attachment/detachment atomistic processes, which are the active Monte Carlo events, dependent on the atom configurations and on the experimental conditions. We present the method and provide some case studies, highlighting the difference between PVD and CVD processes and the dependence of growth rates on process parameters - e.g. nature and pressure of precursors and carrier gases, temperature, substrate orientation. Quantitative predictions of the microstructural evolution of the studied systems can be compared with the structural characterization of actual samples.

Resume : The optical and electronic properties of metal oxide nanocrystals (MO NCs) strongly depend on the surface depletion regions, derived from the presence of surface states. Moreover, MO NCs exhibit a localized surface plasmon resonance (LSPR), offering tunable characteristics enabled by doping, or via electrochemical or photochemical charging. Dynamic control over the LSPR makes MO NCs promising for several optoelectronic and storage applications. For these reasons, by manipulating the NC depletion width, it is possible to control the features of the NC. However, the mechanism behind this phenomenon is very complex, and not yet fully understood. In particular, it is possible to engineer the depletion region by varying various parameters, including the material under consideration, the size of the NCs, the presence of multiple core-shell systems, etc. To do this, it is possible to calculate the band and carrier density profiles for NCs with different features. In this work, a new framework has been introduced that can predict the behavior and physics under the MO NC photodoping process, revealing that the charging mechanism is unexpectedly based on the electronic rearrangement of the energy bands. Numerical simulations were experimentally supported by studying the case of a core-shell structure of Sn:In2O3/In2O3 NCs, by tuning the thickness of the shell, as well as post-synthetically, both by photodoping and reversible chemical reactions. The engineering of the depletion layer and the consequent manipulation of the electronic structure allows to significantly increase the sensitivity of LSPR and to target specific properties in MO NCs. The fine-tuning of the NCs? band structure has enabled an improvement in charge storage capacity, which represents a step towards fully light-driven energy storage devices.

Resume : Hybrid perovskites like (C4H9NH3)2PbI4 have fascinating layered crystal structure with periodic nanoscale interfaces between the inorganic {PbI4}2- and organic C4H9NH3+ layers. Because of these interfaces, electron and hole are confined in atomically thin {PbI4}2- inorganic well layers. Therefore, these layered perovskites are considered as electronically 2D systems, irrespective of their crystallite sizes.1,2 Importantly, the crystal structure is flexible, allowing a number of combinations of different organic cations and inorganic anions. So a rational design of the nanoscale interfaces, and hence, tunable optoelectronic properties are feasible. For example, excitonic binding energy can be controlled over an order of magnitude from a few tens of meV to a few hundreds of meV, with simple variation of composition of organic cations. Furthermore, one can introduce new intermolecular chemical interactions between organic cations, resulting into completely water stable low dimensional hybrid perovskite.3 In this talk, I will discuss about how controlling nanoscale interface between organic and inorganic layers can yield interesting optical, optoelectronic and chemical properties.4 But note that the nanoscale properties will be discussed using millimeter sized single crystals. 1. ACS Energy Lett. 2018, 3, 2940. 2.Phys. Chem. Chem. Phys. 2021, 23, 82. 3. Angew. Chem. Int. Ed. 2021, DOI: 10.1002/anie.202105883 4. Angew. Chem. Int. Ed. 2020, 59, 11653.

Resume : The compounds belonging to the family of perovskites show a great variety of mechanical, magnetic and optical properties, and for these reasons are nowadays key materials for many technologies, including piezoelectrics, photovoltaic solar cells and photocatalytic systems. Among them, all-inorganic halide perovskites (AIHP) represent an emergent class of material, which has many advantages, such as high stability, outstanding optical properties and low-cost. In particular, our attention is devoted to CsPbBr3 and CsPb2Br5 all-inorganic perovskites, which, unlike hybrid structures, show high performances for photocatalytic and photo-electrochemical degradation processes of different organic dye compounds, and are also exceptional candidates as photocatalysts for organic reactions. In fact, one of the most emerging applications of AIHP materials regards the wastewater purification process of textile effluents from industrial production. In this field, heterogeneous catalysis under light is widely accepted due to its high efficiency, yield of degradation and cost effectiveness. Among the different strategy developed for the AIHP materials synthesis, the surfactants-based solution route is widely applied, which also allows to control the stability and the growth kinetics according to the surface chemical phenomenon and the solubility equilibrium. Herein we report a novel synthetic strategy, which represents a facile, one-step, low-temperature and surfactant free approach to the synthesis of Cs-Pb halide perovskites. The present precipitation approach represents an innovative and interesting strategy of synthesis, which avoids the use of surfactant species and toxic solvents and, taking advantage of the Cs and Pb ?-diketonate compounds as precursors, it allows, reproducibly and selectively, the synthesis of CsPbBr3 and CsPb2Br5 perovskite phases. The final products are influenced by the synthetic parameters such as aging time and heating treatment. Structural, morphological and compositional analyses of the final products have been addressed through X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) analysis. Moreover, as a proof-of-concept, the photocatalytic properties of degradation processes have been tested using organic dye solutions, under both UV lamp (?:360 nm) and visible light source.

Resume : Cesium Lead halide perovskite nanocrystals are one of the most promising candidates for portable lasers and light sources. In order to harness this potential, the nanocrystals are often accompanied by a photonic environment that helps manage and improve the light emission. In this work, we report on an efficient quasi-3D photonic crystal composed of a 2D-grating on top of a distributed Bragg reflector (DBR). The optical properties of this quasi-3D system outperform those of each individual component since it supports both a series of Rayleigh-Wood anomalies and a series of guided modes populating the photonic bandgap of the Bragg mirror. In order to demonstrate the improved efficacy of the quasi-3D system in comparison with the alternative 2D-gratings and DBRs, we decorated all the systems with metal halide perovskite nanocrystals and studied the photoluminescence enhancement produced in each case. Interestingly, the quasi-3D system exhibited a PL enhancement of 16 times, exceeding the values observed for the separate components.

Resume : Colloidal lead halide perovskites (LHPs) are relatively new semiconductor materials which are of great interest due to their exceptional optoelectronic properties.[1] They can be classified as all-inorganic or organic-inorganic hybrids of APbX3 formula (where A can be a small-sized organic or metal mono-cation, respectively), and X is a halide anion; they present a three-dimensional (3D) inorganic framework. LHPs can also be prepared with other stoichiometries and different morphologies.[2] Thus, two-dimensional hybrid Ruddlesden–Popper (2D-RPs) lead halide perovskite (LHPs) nanostructures[3] are cutting-edge; they present a L2[APbX3]n−1PbX4 formula, where “L” usually represents a long-chain alkyl or aromatic ammonium ligand and “n” is an integer which stands for the number of atomic lead halide layers held together by weak van der Waals interactions, and sandwiched between organic layers. They exhibit different features from those of typical 2D perovkites: i) they are integrated by quantum well structures, thus exhibiting a strong quantum confinement due to their thickness (below the Böhr radius of the material); ii) the quantum confinement occurs without physically thinning the material down to the atomic thickness; and consequently iii) the emission peaks appear at the same wavelength as long as the [An−1PbnX3n+1] layer thickness is homogeneous, independently of its lateral dimensions; iv) the excitonic absorption and emission peaks are exceptionally narrow, with a small Stokes shift (<10 meV). Ruddlesden-Popper LHPs can be scaled down to a single quantum well dimension, which have low chemical stability as they tend to evolve to a mixture of quantum wells with different lead halide thicknesses and even to 3D material. The preparation of highly (photo)chemical and colloidal stable hybrid LHP nanosheets of m lateral size and 2.5 nm in height with a deep blue emission will be presented. The strategy of stabilizing the colloids for more than 8 h, storing them in the solid state for more than one year, and recovering the blue emissive colloid from the solid as needed will be discussed. References [1] doi.org/10.1021/acsnano.0c08903 [2] a) J. Song, L. Xu , J. Li , J. Xue , Y. Dong , X. Li , H. Zeng, Advanced Materials 2016, 28, 4861–4869. b) S. Gonzalez-Carrero, G. M. Espallargas, R. E. Galian, J. Pérez-Prieto, Journal of Materials Chemistry A 2015, 3, 14039-14045. c) M. C. Weidman, A. J. Goodman, W. A. Tisdale, Chemistry of Materials 2017, 29, 5019-5030. [3] C. C. Stoumpos, D. H. Cao, D. J. Clark, J. Young, J. M. Rondinelli, J. I. Jang, J. T. Hupp, M. G. Kanatzidis, Chemistry Matererials 2016, 28, 2852−2867. Acknowledgments. The work was supported by Ministerio de Economía, Industria y Competitividad (CTQ2017-82711-P, PID2020-115710GB, co-financed by FEDER; FPU17/ 05564, IRP), Ministerio de Ciencia e Innovación (Unit of Excellence “Maria de Maeztu” CEX2019-000919-M), and Generalitat Valenciana (IDIFEDER/2018/064 and PROMETEO/2019/080, GRISOLIAP/2019/041, RCT),c o-financed by FEDER).

Resume : Chirality in semiconductor materials enables a number of powerful applications, reaching from consumer electronics and 3D displays to drug screening and encryption [1-3]. Lately, chiral hybrid perovskites have emerged as a promising class of materials for optoelectronic applications based on their ability to preferably absorb and emit one type of circularly polarized light. However, so far, the chiral organics used to introduce chirality into lead halide perovskites almost exclusively consist of a small group of commercially available, primary amines [1]. In nature, chirality is most prominently found in amino acids. These represent a diverse group of organic compounds whose application for industrial production is highly desirable as they are non-toxic, biodegradable and are available in large quantities at relatively low cost. We now introduce the chiral small organic 3-aminobutyric acid into the 1D perovskite dimethylammonium lead iodide (DMAPbI3) using a simple spin coating based approach. We find that the resulting material displays strong circular dichroism in the blue spectral region that is tunable in strength by adjusting the amount of amino acid introduced. We resolve the detailed structural origin of the chirality from single-crystal XRD experiments of the crystal structure. We employ transient optical spectroscopy to investigate the dynamics of excited state polarization and decay. Our findings expand the pool of chiral hybrid materials and provide fresh impulses for future maximization of chiral effects in hybrid perovskite materials. [1] G. Long, R. Sabatini, M. I. Saidaminov, G. Lakhwani, A. Rasmita, X. Liu, E. H. Sargent, W. Gao Chiral-perovskite optoelectronics. Nat. Rev. Mater. 5, 423?439 (2020). [2] B. Thaom, X. Gao, K. Pan, J. Deng Chiral Helical Polymer/Perovskite Hybrid Nanofibers with Intense Circularly Polarized Luminescence. ACS Nano 15, 7463-7471 (2021). [3] C. Chen, L. Gao, W. Gao, C. Ge, X. Du, Z. Li, Y. Yang, G. Niu, J. Tang Circularly polarized light detection using chiral hybrid perovskite Nat. Comm. 10, 1927 (2019).

Resume : Hybrid halide perovskite semiconductors exhibit nearly ideal properties for myriad optoelectronic applications, including photovoltaics, light emission, and radiation detection. Curiously, these properties coexist with complex, organic cation-derived dynamic disorder and extensive chemical substitution. Furthermore, it appears that both dynamics and substitution enable and improve the functional performance. Neutron scattering and nuclear spectroscopy studies of these materials have yielded significant insight to the nature of the organic cation dynamics and how these dynamics are impacted by chemical substitution. In methylammonium-based materials, substitution tends to impede dynamics, thus resulting in orientational glass behavior. While substitution disrupts cooperative phase transitions in formamidinium-based materials, substitution preserves the local behavior of formamidinium. The retained dynamics and polarizability is advantageous for screening charged defects and myriad other behaviors thought to be responsible for the potentially transformative behavior of these solution-processable, high-performance materials. The dynamic degrees of freedom of the hybrid halide perovskites provide additional opportunities for application engineering and innovation not found in conventional compound semiconductors.

Resume : One of the main goals for perovskite materials is to approach ideal efficiency limits in solar cells or LEDs: being the radiative decay of optical excitations unavoidable, this can be done by reducing contributions from traps and defects. Despite all the advances in device performances, the bimolecular radiative recombination rate in metal halide perovskites is still not clearly established: coefficients derived under different assumptions can take very different values, and a lively debate is going on trying to conjugate their exceptionally long excitation lifetimes with large optical absorption coefficients. Here we provide a calibrated radiometric measurement of the instantaneous photoluminescence flux emitted by thin-films of hybrid perovskites with controlled carrier density under pulsed excitation. In all the analysed samples we uncover a radiative recombination rate much lower than the bimolecular recombination coefficient, revealing the presence of non-radiative bimolecular recombination rate that can be attributed to a population of dark states. Our findings suggest that to minimize unwanted decay channels for optical excitations one should also take account of this non-radiative contribution to the bimolecular decay, that is due to extrinsic effects, like trapping and defects, and can be substantially reduced with materials optimization.

Resume : Halide perovskite nanocrystals (NCs) have emerged as an intriguing material for optoelectronic applications, most notably for light-emitting diodes (LEDs), lasers, and solar cells. Their emission wavelength can be tuned with material composition and size as well as dimensionality, as in the case of two-dimensional (2D) nanoplatelets (NPls). These colloidal quantum wells have additional appeal for light emission, as the one-dimensional quantum confinement enhances their radiative rates and enables directional outcoupling. On top of this, due to a monolayer-precise control over their thickness, they constitute an intriguing system for spectroscopic studies on their fundamental optical, phononic, and energetic properties. In this talk, I will explore the recent results on halide perovskite nanoplatelets, including their synthesis. I will focus on their interesting excitonic properties, as these govern the interaction significant in light-emitting applications. Presenting the newest insights gained from optical spectroscopy and theoretical modeling, I will conclude by showing how these intriguing nanocrystals can be integrated into optoelectronic devices.

Resume : Metal halide perovskites have drawn increasing attention as photodetector materials due to their strong light absorption and resulting photocurrent.[1] More specifically, the sensitive detection of X-rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for X-ray imaging. In addition to lead-based perovskites, the lead-free double perovskite Cs2AgBiBr6 system has gained significant attention for photodetection due to the facile processing in combination with outstanding properties, such as high X-ray sensitivity,[2] high carrier mobility, and high stability. We aim to detail the dynamics and transport of the photogenerated charges that govern the photoresponse, relying on a set of high-resolution structural and optical spectroscopic tools.[3,4] Moreover, we demonstrate the importance of manipulating the perovskites’ microchemistry and intrinsic charge carrier dynamics to enhance the photoresponse toward an improved material platform for next-generation imaging.[5] Ultimately, to integrate perovskites in practical devices, controlled deposition and patterning is a critical step. We demonstrate the development of an all-evaporated structure or a dry lift-off process to fabricate air-stable perovskite photodetector arrays on both glass and flexible substrates, with a pixel resolution down to 5 μm.[6,7] 1. Clinckemalie, L.; … Debroye, E. Challenges and opportunities for CsPbBr3 Perovskites in Low- and High-Energy Radiation Detection. ACS Energy Lett., 2021, 6, 1290, 10.1021/acsenergylett.1c00007 2. Steele, J. et al. Photophysical Pathways in Highly Sensitive Cs2AgBiBr6 Double Perovskite Single-Crystal X-Ray Detectors. Adv. Mater., 2018, 30, 46, 1804450, 10.1002/adma.201804450 3. Zhang, H.; Debroye, E. et al. Highly Mobile Large Polarons in Black Phase CsPbI3. ACS Energy Lett., 2021, 6, 2, 568, 10.1021/acsenergylett.0c02482 4. Zhang, H.; Debroye, E. et al. Highly Mobile Hot Holes in Cs2AgBiBr¬6 Double Perovskite. Submitted 5. Keshavarz, M.; Debroye, E. et al. Tuning the Structural and Optoelectronic Properties of Cs2AgBiBr6 Double Perovskite Single Crystals Through Alkali Metal Substitution. Adv. Mater., 2020, 32, 40, 2001878, 10.1002/ adma202001878 6. Pintor, I. et al. All-Evaporated, All-Inorganic CsPbI3 Perovskite-based Devices for Broadband Photodetector and Solar Cell Applications. ACS Appl. Electron. Mater., 2021, 10.1021/acsaelm.1c00252 7. Xia, B. et al. Flexible Metal Halide Perovskite Photodetector Arrays via Photolithography and Dry Lift-off Patterning. Submitted

Resume : The communication technology during the back centuries used the Morse code for transmitting coded signals. In late 1800, the message was transmitted in an efficient speed manner with help of Morse code communication from one area to another was delivered via telegraph wires where the dots and dashes combination would serve as each alphabet or number. The triboelectric nanogenerator is a widely preferred energy harvesting device that allows a wide variety of material selection, cheap fabrication, and low-frequency operation. The main advantages of this work are to eradicate the use of battery which have low life cycles and create an abundance of waste pollution. The nanogenerators could be a sustainable power source contributing its role to solve the partial energy crisis. Sr3CO2WO9 (SCWO) is synthesized by an aqueous sol-gel reaction. The cubic symmetry and Fm-3m space group of SCWO are shown by XRD analysis. The microstructure of PDMS-SCWO particles confirms the particles are distributed all over the PDMS. Triboelectrification is a phenomenon in which two materials bearing different polarity either rub or due to friction could accept or donate electrons leading to the generation of electrical output. These particles have a high dielectric constant and low loss make triple perovskite a promising candidate for TENG. A vertical contact separation triboelectric nanogenerator could produce voltage and current of 300 V and 2.2 ?A for 10 wt% polydimethylsiloxane ? Sr3Co2WO9 (PDMS-SCWO) composite film. The power density of the rough surface TP-TENG was 30.5 ?W/cm2, which is many times enhancement as compared to the power density of 5.5 ?W/cm2 of plain surface TP-TENG. Furthermore, the output is stable for TP-TENG making it a potential candidate for information signaling (Morse code) in real-time applications.

Resume : During the last decade, the demand in nanophosphors has dramatically increased for addressing the requirements needed for several applications. In particular, nanosized phosphors with efficient optical properties have attracted much attention since they can be used in high-performance displays as well as fluorescent probes in nanomedicine or for specific shaping such as 3D printing with ink-jet techniques. Two distinct approaches can be considered for their design, the bottom-up (assembly from molecules) or the top-down strategies (size reduction to nanoscale). In this talk, I will illustrate both approaches for synthesizing several types of nanosized phosphors, i.e. inorganic (oxide and fluoride), organic-inorganic hybrids (organic dye encapsulated into silica nanoparticles) and semi-conductor nanocrystals (Quantum Dots or QDs). In particular, the preparation of Y3Al5O12:Ce3+ and NaYF4:Yb3+,Tm3+ nanoparticles and their implementation as respectively yellow-emitting phosphor for LED devices based on microLEDs (LED) and up-converting phosphor in the infrared range for medical imaging will be discussed. Furthermore, the development of luminescent hybrid nanoparticles composed of fluorescein entrapped into silica matrix by reverse microemulsion method will be presented. Finally, the last part will be devoted to a family of Cd-free QDs, constituted of InP cores coated with a ZnS shell, which are of great interest due to the size dependence of their outstanding optical properties.

Resume : The quest for revealing new or improved functionalities in ferroelectric materials is at its peak nowadays. The new non-lead ferroelectric thin films were intensively developed in last years for application in the field of optics, electronics, sensing or harvesting solar energy. In this work we present the proprieties of different class of ferroelectric thin films, with different crystalline structures, obtained by Pulsed Laser Deposition (PLD) having tailored properties needed in photonics, electronics or sensing field. The use of PLD technique emphasizes the importance and the role of chemical pressure and epitaxial strain fine stoichiometric changes induced into the lead-free ferroelectrics as a result of either doping or of the lattice misfit between the lattice parameter of perovskites films and the used substrates on the enhancement of optical and electrical properties in thin films. The crystalline properties of the thin films thus obtained were studied using X-ray diffraction. The optical properties and the thicknesses of composing layers were investigated by spectroscopic ellipsometry (SE). Furthermore, the dependence of optical, electric and magnetic properties depending on temperature was determined. Acknowledgements: This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI ? UEFISCDI, project number PN-III-P4-ID-PCE-2020-2921, within PNCDI III

Resume : Organic-inorganic halide perovskite nanocrystals (PNCs) are gaining increasing attention in contemporary research due to their promising performance in light-emitting as well as solar technology. Photoexcitation of these PNCs with an ultrashort laser pulse can produce coherent phonons along the lattice displacement coordinate, leading to lattice vibrations. Here, we employ femtosecond pump-probe spectroscopy to initiate the photophysics by the formation of coherent phonons and to observe the subsequent coherent vibrational dynamics of formamidinium lead halide (FAPbX3, X=Br, I) PNCs.[1] We find that the FAPbX3 PNCs generate halide-dependent coherent vibronic wave packets upon non-resonant excitation, and the dominant contributions are attributed to the Pb–X bending and stretching modes of PbX64- octahedral units of the lattice. More importantly, for the first time, we observe higher harmonic vibrational modes in FAPbI3 PNCs, which points to a more anharmonic potential energy surface in the case of FAPbI3 as compared to FAPbBr3 PNCs. This is likely due to the weaker interaction between the central FA moiety (which sits in a larger octahedral interstitial site) and the inorganic cage for FAPbI3 PNCs, and thus the PbI64- unit can vibrate more freely. This weakening reveals the intrinsic anharmonicity in the Pb-I framework, and thus facilitating the energy transfer into overtone and combination bands. Furthermore, our control experiment with MAPbBr3 reveals the energy transfer between framework phonons due to the intrinsic anharmonicity of the lead-halide framework is indeed influenced by the interaction between the framework and the organic molecules, and not only by the halide nature. The insights interestingly not only unravel the underlying reason for the halide-dependent stability of these materials but also shed light on their charge-carrier mobility and light emission properties. References [1] T. Debnath, D. Sarker, H.Huang, et al. Nat. Commun. 12 (1), 2629 (2021).

Resume : Due to their exceptional optoelectronic properties, all-inorganic lead halide perovskites offer enormous potential for next generation photonic, light-emitting, and optoelectronic devices. However, their usage is significantly limited by their poor stability upon moisture exposure and lead toxicity issues. Moreover, it has been recognized that the development of confined perovskite micro-patterns of various shapes and periodicities is essential towards expanding the application range. Herein we report a simple, low-temperature, post-glass melting encapsulation method that enables the controlled incorporation of highly photoluminescent cesium lead bromide perovskite nanocrystals within silver phosphate glass (AgPO3). Such host glass is transparent in most of the visible range, thus allowing full exploitation of the developed composite glasses towards optoelectronic and photonic devices. The reported fabrication protocol relies on a simple melting encapsulation process in which pre-synthesized perovskite crystals are inserted in the glass matrix, following the initial glass quenching. Based on this novel approach, two types of composite perovskite glasses are prepared, one that hosts perovskite isles and the second in which thin perovskite layers of few nm are embedded beneath the glass surface. Both types of composite glasses exhibit remarkable photoluminescence stability when compared to the ambient air-exposed perovskite crystals. More importantly, by means of a simple and fast cw-laser processing technique, we demonstrate the development of encapsulated dotted perovskite micropatterns within the composite perovskite glass. The ability of the proposed system to resolve stability and lead toxicity issues, coupled with the facile formation of encapsulated highly luminescent perovskite patterns pave the way towards the broad exploitation of perovskite crystals in various photonic applications.

Resume : The development of highly functional materials for light emission and/or amplification is a research field in constant expansion; in particular, high-density semiconductor nanowires slabs represent promising systems attracting a considerable scientific interest for applications in light sources, sensing and photovoltaic devices [1]. The spatial arrangement of nanowires in new disordered textures can drive exciting optical phenomena. This is because their very multiple scattering nature and the light transport properties allow optical performances often superior to those offered by ordered photonic structures [2]. On the other hand, the diffusive propagation of light through these disordered materials gives rise to fascinating and unexpected interference phenomena surviving also in the inelastic scattering regime [3]. Here we will present recent experimental results where disordered arrays of silicon nanowires are used to generate and beam directional coherent Raman light [4]. We show the direct visualization of the weakly localized Raman radiation by both real- and momentum-space microscopy, that permitted us to gain insight on the mechanisms ruling the light transport through the random media. These results pave the way for the development of next generation of new light sources based on both the coherent control of directional beaming and the fine frequency tuning. References: [1] Priolo F. et al., Nat. Nanotech. 9, 19 (2014) [2] B. Fazio, P. Artoni, M.A. Iatì, C. D'Andrea, M.J. Lo Faro, S. Del Sorbo, S. Pirotta, P.G. Gucciardi, P. Musumeci, C.S. Vasi, R. Saija, M. Galli, F. Priolo, and A. Irrera. Strongly Enhanced Light Trapping in a Two-dimensional Silicon Nanowire Random Fractal Array. Light: Science & Applications,5: e16062, 2016. [3] B. Fazio, A. Irrera, S. Pirotta, C. D’Andrea, S. Del Sorbo, M.J. Lo Faro, P.G. Gucciardi, M.A. Iatì, R. Saija, M.Patrini, P. Musumeci, C.S. Vasi, D.S. Wiersma, M. Galli, and F. Priolo. Coherent Backscattering of Raman Light. Nature Photonics 11: 170-176, 2017. [4] M.J. Lo Faro, G. Ruello, A.A. Leonardi, D. Morganti, A. Irrera, F. Priolo, S. Gigan, G. Volpe, and B. Fazio. Visualization of directional beaming of weakly localized Raman from a random network of silicon nanowires. Advanced Science, 2100139, 1-11, 2021. DOI 10.1002/advs.202100139.

Resume : Wet chemical synthesis is a very versatile method to obtain Au and Ag particles with an astonishing shape diversity, largely through the use of various additives, each of them fulfilling one or several roles. In this framework, I will focus on bimetallic Au/Ag nanoparticles, whose properties are rendered even more diverse by the combination of the two constituents. For instance, depositing Ag on pentatwinned Au bipyramids (AuBPs) is an efficient way to form Ag nanorods (AgNRs) with controllable aspect ratio which can be increased significantly upon controlled Ag addition, shifting LSPR from the visible to the infrared region. In a first work, we have shown an unexpected double role of ascorbic acid in this synthesis by using a combination of time resolved techniques.(1) AgNRs were prepared in which the gold bipyramid was located at the center of mass of the NPs. In a recent work, we developed a method in mixed solvent to break the inversion symmetry of the AgNRs by displacing the seed position at one tip of the AgNR. We propose a mechanism to understand the Ag deposition on the gold surface which is supported by experimental evidence and molecular dynamic (MD) simulations.(2) 1. Aliyah, K.; Lyu, J.; Goldmann, C.; Bizien, T.; Hamon, C.; Alloyeau, D.; Constantin, D., J. Phys. Chem. Lett. 2020, 11 (8), 2830-2837. 2. Goldmann, C.; de Frutos, M; Hill, E.; Constantin, D.; Hamon, C., Chem. Mater. 2021, ASAP

Resume : Sub-10 nm quasi-one dimensional (1D) nanostructures have received increasing interest for their use as small basic building units in nanodevices. One dimensional Silver (Ag) nanostructures, as one of the promising candidates for electronics, plasmonics and sensing applications, have been fabricated by a variety of chemical and physical strategies. However, preparing sub-10 nm (diameter) 1D Ag nanostructures for nanofabrication remains challenging experimentally and the nucleation and growth dynamics of the Ag nanowires are still not fully understood (1-4). In this work, we report the segregation-driven in situ generation of Ag NWs on the surface of a Ag2WO4 (AWO) nanorod (NR) under electron beam irradiation in an aberration corrected-TEM (AC-TEM). We adopted AWO as the starting material because previous studies have demonstrated Ag surface segregation and the formation of Ag NPs on the oxide support under plasma or electron beam irradiation (5-7). By controlling the electron irradiation dose rate, sub-10 nm Ag NWs (9.5 ± 0.2 nm) are fabricated on the oxide surface. The generated Ag NWs show a tunable length/diameter aspect ratio, and the formed surface in the NWs is the low-energy {111} plane. The direct in situ observations on the nucleation and growth dynamics uncover that the sub-10 nm silver NWs show a combined growth process of linear first-order kinetics and nonlinear second order kinetics in the lateral direction and the electron dose rate plays an important role in regulating the diameter of the supported Ag NWs (8). The ability to fabricate Ag NWs in a controllable way by using electron beam irradiation represents a significant step forward to the further applications of Ag NWs in nanodevices. The present study opens a new avenue for the fabrication of sup-ported sub-10 nm Ag nanowires through an electron beam irradiation nanofabrication route and highlights the importance of irradiation dose- and dynamics controlled materials growth. References: 1. J. Li, et al., Nanoscale Horiz., 2019, 4, 1302–1309. 2. J. Li, Z. Wang and F. L. Deepak, ACS Nano, 2017, 11, 5590–5597. 3. J. Li, et al., Adv. Sci., 2018, 5, 1700992. 4. J. Li, et al., J. Phys. Chem. Lett., 2018, 9, 961–969 5. J. Li, Z. Wang, Y. Li and F. L. Deepak, Adv. Sci., 2019, 6, 1802131. 6. M. d. Assis, et al., Sci. Rep., 2019, 9, 9927. 7. R. A. Roca, et al., Inorg. Chem., 2016, 55, 8661–8671. 8. Junjie Li and Francis Leonard Deepak, Chem. Commun., 2020, 56, 4765.

Resume : The possibility of designing composite Gallium-Arsenide (GaAs) nanowires structures via bottom-up methods has attracted significant interest for the engineering of future optoelectronic devices [1]. The crystal structure and the stacking fault density of GaAs nanowires largely determine their optoelectronic properties [2]. Here, we present an investigation of the structural and optical properties of GaAs nanowires. GaAs nanowires were grown by metal-organic vapour phase epitaxy (MOCVD) on GaAs (111)B substrates initially patterned using selected area epitaxy (SAE). Transmission electron microscopy (TEM) shows that GaAs nanowires have a ZB structure with a varying twin defect density (TDs) along the nanowire’s length. The average local twin defect density (ntdd), computed for a section length of 1 µm along the NW’s axis, decreases from 110 to 13 #/µm from the base to the tip of the NW. To correlate the GaAs NW crystal structure to its electronic band structure, cathodoluminescence (CL) and time resolved photoluminescence measurements were done at room temperature. The CL intensity increases by 14 times from the bottom to the NW’s tip, while the CL peak position shifted from 897 nm (1.382 eV) to 886 nm (1.399 eV). The CL peaks red-shift along the NWs vertical axis is tentatively attributed to type-II band alignment at the ZB-TD-ZB interfaces. The high surface recombination velocity of GaAs is a major issue for applications in optoelectronic devices. As a result, passivation of the nanowire surface is required for various applications such as lasing. Here, however, we demonstrate that when sufficient nanowire’s length and optimal structural properties are obtained, pure unpassivated GaAs nanowires can achieve low-temperature lasing. This provides insights towards the engineering of GaAs NW for applications in optoelectronic devices. [1] H. Li, Y. Chen, Z. Wei, and R. Chen, ‘Optical property and lasing of GaAs-based nanowires’, Sci. China Mater., vol. 63, no. 8, pp. 1364–1381, 2020. [2] M. Heiss et al., ‘Direct correlation of crystal structure and optical properties in wurtzite/zinc-blende GaAs nanowire heterostructures’, Phys. Rev. B - Condens. Matter Mater. Phys., vol. 83, no. 4, pp. 1–10, 2011.

Resume : GeSn alloy is the most interesting binary material within group IV-based semiconductor family which opens up a possibility for achieving direct bandgap at typical values of Sn ranging from ~ 6 –11%. Unfortunately, increasing the Sn composition in solid GeSn remains a challenging task due to the miscibility gap at typical growth temperatures, lattice mismatch issues and Sn segregation. Nanowires (NWs) exhibit great properties such as efficient strain relieving capability and excellent crystalline quality. That is why GeSn NW grown by different techniques have recently gained much attention. However, even in NWs one should compromise between the increased Sn composition and the spatial homogeneity along the GeSn NW crystal. The most commonly used method to grow NWs with a high degree of crystal quality is the Vapor-Liquid-Solid (VLS) mechanism. It is shown that the composition of a catalyst droplet influences many properties of VLS semiconductor NWs, including their crystal phase, doping, growth rate, chemical composition, growth direction and morphology. This presentation will focus on a comprehensive study of VLS-CVD grown GeSn nanowires with different catalyst droplets composition, combining the growth technology, complementary chemical and structural analyses and theoretical modeling. The influence of growth conditions such as temperature, vapor phase composition and liquid phase composition on the crystallization rate of both Ge and Sn from the liquid to the solid phase will be discussed. The end result shows that Sn incorporation with a high degree of homogeneity along the NW can be improved by adding some specific foreign elements in the liquid droplet. This is achieved by understanding the kinetics and the thermodynamic in the liquid phase, and coupling them with the kinetically controlled composition of solid nanowires. Overall, these findings provide a convenient method to control the composition and the homogeneity of GeSn NWs by adding suitable foreign atoms to the catalyst droplets and this pave new ways for fabrication of cheap and highly efficient nano- and opto- electronic devices on Si electronic platform.

Resume : Nanostructured WO3 represents a promising material for the realization of fast and reliable H2 sensors based on chemoresistive effect, even if the mechanism regulating the interaction between WO3 and H2 is not completely understood. A simple and low-cost technique to get well controlled WO3 nanorods would represent a key element for H-related applications. A powder of WO3 nanorods (400 nm long, 5 nm large) is produced by hydrothermal technique and drop casted onto Pt interdigitated electrode. XRD analysis confirms hexagonal crystal structure. The chemoresistive behaviour is investigated in the 250-400°C temperature range and for 2000-50000 ppm of H2 concentrations and the measured response transients have been successfully modelled within the Langmuir theory by hypothesizing two independent active processes: a fast process (below 4 s) which is attributed to interaction with adsorbed oxygen at WO3 nanorods surface and a slower process (20-1000 s) which occurs through oxygen vacancies generation in bulk WO3 [1]. H intercalation in WO3 is ruled out. The chemoresistive effect leading to H2 sensing by WO3 is explained through the above processes, whose kinetic barriers have been quantified. These data open the route for development of fast, sensitive and low-temperature operating H2 sensor based on WO3. [1] G. Mineo, K. Moulaee, G. Neri, S. Mirabella, E. Bruno, H2 detection mechanism in chemoresistive sensor based on low-cost synthesized WO3 nanorods (submitted to Sensor and Actuators B: Chemicals)

Resume : Recent detailed investigations of the formation mechanisms of centrosymmetric metal oxide nanoparticles such as TiO2 and ZrxTi1-xO2 have evidenced the appearance of oxo-alkoxy clusters that further aggregate into amorphous nuclei at low hydrolysis rates of alkoxide precursors [1?3]. In this work, a mixture of LiOEt and Nb2(OC2H5)10 diluted in alcohols and glycols of different chain lengths has been used to produce non-centrosymmetric LiNbO3 nanocrystals. Upon hydrolysis of the initial precursor solutions kept under magnetic stirring, DLS measurements demonstrate the rapid formation of ~2nm oxo-clusters for each solvent after ligand exchange with the initial ethoxide precursors. After 24h at room temperature and formation of a viscous clear gel, SAXS measurements confirm the presence of ?amorphous? nuclei of average diameter ~4nm. A solvothermal treatment at 235°C for 24h then results in the formation of LiNbO3 nanocrystals whose average crystallite size continuously decreases from 24 to 15 nm when the chain length of the co-solvent is increased from ethanol to heptanol. Time- and temperature-dependent experiments of the solvothermal treatment also reveal the presence of a not yet-identified, crystallized reaction intermediate. Finally, colloidal suspensions of Er-doped and Er-Yb co-doped nanocrystals evidence scattering of several nonlinear optical (SHG, THG and SFG) and up-conversion (UC) signals.

Resume : Sb-based quantum dots with large, single-hole confinement are promising candidates for quantum dot flash memories. We analyzed the size, shape, and composition of highly strained (InGa)(AsSb) Stranski-Krastanov quantum dots (SKQDs) embedded in a GaP matrix with atomic resolution by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography. The sample investigated in this work is exactly the same as the one with a storage time record for metal-organic chemical vapor deposition (MOCVD) grown heterostructures of 1 hr at room temperature, measured via deep-level transient spectroscopy. These quantum dots have a truncated pyramid shape with a base length of 8.5 nm and a height of 3 nm. The core of the QD is uniform with no alloy fluctuations but intermixing is observed close to the QD edges. The QDs occur at a very high density of ~4×10^11 cm^-2 compared to conventional InAs SKQDs. Finite element (FE) simulations are performed, using structural data from X-STM, to calculate the strain and the outward relaxation of the cleaved QDs. FE simulations together with X-STM results are used to estimate the composition of the QDs i.e., ∼In0.3Ga0.7As0.85Sb0.15. A similar ratio of 2:1-In:Sb was observed from atom probe experiments, which is in good agreement with FE simulations, and previous optical, electrical, and theoretical studies. The results prove that the InGaSb and GaAs layers have strongly intermixed during the QD formation. A detailed analysis of the capping layer is performed showing the segregation of Sb and In atoms from the QD layer into the capping layer. Overall, the current study provides a detailed structural and compositional overview of these novel QDs, shedding light on the Sb incorporation into the QD-layer and provides valuable feedback to the MOCVD growth of Sb-based QDs, to optimize the storage time of QD-Flash memory devices.

Resume : In the race for miniaturization of optical systems like lighting or display devices, the development of luminescent nanoparticles with high quantum yields and covering a wide colour-range represents a crucial issue. Colloidal quantum Dots (QDs) seem to meet all the requirements for such applications. QDs have generally a diameter lower than 10 nm and exhibit size-tunable optical properties. Nowadays, in lighting and display technologies, QDs exhibiting the best stability under continuous irradiation (UV) and the highest optical performances contain cadmium, a strongly toxic and RoHS[1]-prohibited chemical element. The purpose of the present work is to develop a Cd-free family of QDs through the very popular hot-injection method allowing fine control of stoichiometry, size and size distribution of the nanocrystals. To this end, we have synthesized indium phosphide (InP) QDs from indium halides and aminophosphine precursors. [2] We have identified a specific diamine yielding tetrahedral QDs with adjustable edge lengths from ~ 3 to 6 nm, as confirmed by UV/Visible spectroscopy and dark field transmission electron microscopy. The underlying mechanisms are clarified by combining 31P liquid NMR and UV/Visible spectroscopies. After coating with a ZnS shell, the InP/ZnS QDs demonstrate fluorescence from 480 to 620 nm with photoluminescence quantum yield (PLQY) in the 45 – 60 % range depending on the experimental conditions. [1] Restriction of hazardous substances in electrical and electronic equipment: European directive (2002/95/CE). [2] Tessier et al. Chem. Mater. 2015, 27, 4893-4898.

Resume : Group IV quantum dots (QDs) are attractive for non-volatile memories considering compatibility with CMOS technology [1]. Here, we use alloy SiGeSn QDs as charge storage nodes with advantages of low thermal budget for formation, high stability (little Si to GeSn) and adjustable composition. Our approach for QDs-based non-volatile memory consists in magnetron sputtering of 3-layers stack of gate HfO2/intermediate SiGeSn-HfO2/tunnel HfO2 on Si wafer, followed by RTA for nanostructuring, meaning the formation of SiGeSn QDs in floating gate (FG) [2,3]. High-k dielectric HfO2 lends itself to non-volatile memories, being a standard material in semiconductor processing. So, we achieve the formation of ~5 nm Ge-rich SiGeSn QDs in FG with 5% Si content and diamond structure (high resolution transmission electron microscopy, Raman spectroscopy). SiGeSn QDs contain small amount of Sn (2%) in FG, while at the interface of FG with adjacent layers (gate and tunnel HfO2), Sn amount is much increased to 15%. This can be explained by Sn atoms diffusion and segregation to the FG interfaces taking into account that Sn presence favours SiGeSn crystallization process (decreasing crystallization temperature). The memory capacitors (Al contacts) present capacitance-voltage hysteresis loops with high frequency-independent memory window of 3–4 V produced by charge storage in SiGeSn QDs. [1] Z. Lv, Y. Wang, J. Chen, J. Wang, Y. Zhou, S.-T. Han, Chem Rev 120, 3941 (2020) [2] C. Palade, A. Slav, A.M. Lepadatu, I. Stavarache, I. Dascalescu, V.A. Maraloiu, C.C. Negrila, C. Logofatu, T. Stoica, V. Teodorescu, M.L. Ciurea, S. Lazanu, Nanotechnology 30, 365604 (2019) [3] C. Palade, A. Slav, A.-M. Lepadatu, A.V. Maraloiu, I. Dascalescu, S. Iftimie, S. Lazanu, M.L. Ciurea, T. Stoica, Appl Phys Lett 113, 213106 (2018)

Resume : The pathway adopted by our group for obtaining group IV-based quantum dots (QDs) / nanocrystals (NCs) for photonics applications is to embed QDs/NCs in oxide matrix [1,2]. This is achieved by magnetron sputtering for deposition of films/multilayers followed by rapid thermal annealing for nanostructuring. Strong quantum confinement effect in Ge NCs is enabled due to high 24 nm Bohr exciton radius, while by alloying Ge with small Si content, the thermally stability of NCs is increased due to diminished fast Ge diffusion. GeSi NCs/QDs represent a very advantageous alternative to III?V semiconductors for group IV photonics as they are CMOS compatible and eco-friendly, and their fabrication by magnetron sputtering is cost-effective and versatile. Here, we focus on Ge QDs and GeSi NCs in TiO2. We show that the sensitivity limit (in spectral photocurrent) is much extended in SWIR up to 1700 nm for GeSi NCs-TiO2 in comparison to 1250 nm for films of Ge NCs embedded in TiO2. The extended SWIR sensitivity is explained by the lower density of non-radiative recombination centers, as in GeSi NCs-TiO2 samples the photocarriers are generated in Ge-rich SiGe NCs stabilized by formation of a thin SiO2 layer at NC/matrix interface [1]. On the other hand, coplanar structures of Ge NCs-TiO2/ SiO2/Si substrate show enhanced photocurrent by field effect with exponential voltage increase due to induced carrier depleted zone [2]. [1] A.-M. Lepadatu, C. Palade, A. Slav, O. Cojocaru, V.A. Maraloiu, S. Iftimie, F. Comanescu, A. Dinescu, V.S. Teodorescu, T. Stoica, M.L. Ciurea, J Phys Chem C 124, 25043 (2020) [2] A.-M. Lepadatu, A. Slav, C. Palade, I. Dascalescu, M. Enculescu, S. Iftimie, S. Lazanu, V.S. Teodorescu, M.L. Ciurea, T. Stoica, Sci Rep 8, 4898 (2018)

Resume : Out of different kinds of solid-state qubits, quantum dot (QD), grown by molecular beam epitaxy (MBE), is a very promising one. Because of the possibility to interface Rb-atom for quantum memory, GaAs QD-emitted single photons, with high brightness and purity, at ~780 nm is highly demanding. On the other hand, achieving highly symmetric dot with a very low fine structure (<1 µeV) in order to generate entangled photons, droplet etching mediated GaAs QD is leading the way. Therefore, presently, GaAs QD is drawing attention of different research groups, even those working with entangled photons out of a nonlinear crystal via spontaneous parametric down conversion, either to use its high pure single photons or entangled photons or both. Here, I will describe about the different growth modes by MBE and novel droplet etching technique as a newer addition to this in order to obtain highly symmetric QDs and to provide a clear view on the difference compared to widely studied InAs QDs on GaAs. I will describe also an implementation of a Yagi-Uda dielectric antenna containing this GaAs QDs to extract more light from it with a privilege of non-deterministic positioning of QDs and different properties of this kind of antenna with a possibility to enhance its strength by surface engineering. I will present relevant optical simulations performed using Lumerical FDTD solutions for this antenna structure along with several other structures like distributed Bragg reflector cavity and bull’s eye cavity to make a comparison with respect to the Purcell enhancement, extraction efficiency, farfield pattern and fabrication challenges. In the end, I will describe about the present ongoing work for blinking free entangled photon source to employ in a quantum key distribution experiment. References 1. Huang H, Manna S*, Schimpf C, Reindl M, Yuan X, da Silva S F C, Rastelli A* (2021) Bright single photon emission from quantum dots embedded in a broadband planar optical antenna (*Corresponding authors). Advanced Optical Materials 9, 2001490 (1-8). 2. Schimpf C, Reindl M, Huber D, Lehner B, Da Silva S F C, Manna S, Vyvlecka M, Walther P, Rastelli A (2021) Quantum cryptography with highly entangled photons from semiconductor quantum dots. Science Advances 7, eabe8905 (1-8). 3. Manna S, Huang H, da Silva S F C, Schimpf C, Rota M B, Reindl M, Trotta R, Rastelli A (2020) Surface passivation and oxide encapsulation to improve optical properties of a single GaAs quantum dot close to the surface. Applied Surface Science 532, 147360 (1-7). 4. Gurioli M, Wang Z, Rastelli A, Kuroda T, Sanguinetti S (2019) Droplet epitaxy of semiconductor nanostructures for quantum photonic devices. Nature Materials 18, 799–810.

Resume : Resonant tunneling[RT] which is a quantum mechanical process has been attracting both scientific and technological attention because of its interesting physics and application for electronics. This phenomenon accompanies negative differential resistance in current-voltage characteristics and has various physical properties that are used in many electronic circuits such as multi-level logic devices. But oxide-based RT study encounters difficulty because of sample instability, crystal quality, and lack of evidence for a mechanism. Here shows negative differential resistance[NDR] by applying voltage and measuring current passing through the SRO/STO SL system. we deliberately designed SrRuO3/SrTiO3[SRO/STO] superlattice[SL]. Using the pulsed-laser deposition, we can control SRO/STO SL with an atomic-scale precision which results in a quantized state of SRO between the STO barrier. Due to the discrete state of the SRO, SRO/STO SL system show [NDR] when Fermi level match with the SRO energy state by applying voltage. Specifically, we changed the thicknesses of STO from 2 to 8-unit cell while that of SRO is fixed to check the evolution of RT. We expect this study opens a possibility of new applications based on the epitaxial thin film oxide.

Resume : Easy and green chemistry production of carbon dots (CDs) that exhibit a precise chirality has attracted great interest nowadays. Chiral nanomaterials are promising for potential applications in enantioselective catalysis, separation and others [1]. CDs can be produced directly by controlled decomposition of appropriate optical pure organic substrates via a bottom-up approach. In particular, aminoacids are among the most investigated classes of chiral starting materials. Cysteine-based chiral CDs have been already applied in several contests with promising performances [2,3]. For these reasons, we investigated a novel catalysed process for preparation of CDs, using Cu(II) ions; the process does not require any thermal treatment and the CDs formation is driven by the production of reactive radical species generated by the catalytic role of the multivalent transition metal [3]. Due to the mild reaction conditions, this synthetic process is particularly suitable for in situ and ex situ investigations. We focused our attention on the processes taking place during the formation of the CDs, with special attention to: 1) role of the metal ion in the decomposition process: the spectrophotometric analyses show direct evidence on the formation of a cysteine-Cu(II) complex that is active in the cysteine oxidation process leading to the generation of oxygen and sulfur radical active species (ROS and RSS); 2) role of the organic substrate structure: by investigating reactions conducted with different organic substrates whose thiyl radical chemistry is known, we recognized a non-trivial role of the radical hydrogen abstraction reactions involved in the formation process of CDs; 3) the evolution of the nanomaterial during the reaction course: this evolution is related to the decomposition of the grafted chiral molecules and the formation of luminophores species on the particle surface; 4) a detailed analysis on the evolution of optical chirality during the synthesis: we related the effects on the chiroptical signal to the formation mechanism of the nanomaterial revealing significant evidence on the chirality origin. Our investigation on this novel synthetic approach for the synthesis of chiral CDs with high control on optical and chiroptical properties paves the way for the design of new chiral nanosystems. [1] Z. Tang, Chiral Nanomaterials: Preparation, Properties and Application, Wiley-VCH, Weinheim, Germany, 1st edn, 2018. [2] L. Hu, et al. Nanoscale, 2018, 10, 2333–2340, 10.1039/C7NR08335A. [3] F. Li, et al. Ang. Chem. Int. Ed. 2020, 59, 11087-11092, 10.1002/anie.202002904. [3] L. Branzi et al. Nanoscale, 2021, 10.1039/D1NR01927A.

Resume : Carbon Nanodots (CDs) are a family of carbon-based nanoparticles endowed with tunable visible fluorescence,1-2 which makes them very promising for light-emitting devices, optoelectronics, photocatalysis, and more. The technological use of CDs is hampered by the difficulty of controlling their optical response, and by a low emission efficiency in the orange-red spectral region, still insufficient for many applications. In fact, the synthesis of efficiently red-emitting CDs remains rare.3 We explored the interactions of CDs with metal nanoparticles (NPs), as a route to enhance their fluorescence. The electromagnetic response of Au and Ag NPs displays well-known plasmonic resonances due to collective oscillations of charge carriers. When these NPs interact with other nanomaterials, plasmonic effects can be used to control the optical response of the resulting coupled nanosystems.4 We devised a simple route to synthesize CD-AuNP hybrids by electrostatic self-assembly in colloidal phase. The spatial separation of CDs from AuNPs in the nano-hybrid can be regulated by a suitable choice of CD surface ligands. Depending on this, the interactions between CDs and AuNPs lead either to a quenching or to an enhancement of the orange fluorescence of CDs. In the right conditions, the plasmonic near-field of AuNPs can be exploited to enhance CD emission of a factor of six. A thorough analysis of CD-AuNP electronic interactions by steady-state, nanosecond and femtosecond time-resolved methods shows that CD fluorescence enhancement is due to ultrafast energy transfer from AuNPs plasmonic states. These findings provide insight on the interactions between metal NPs and fluorescent materials, and open a route to boost the optical response of CDs in the orange-red spectral range. 1 A. Sciortino et al. C 4, 67 (2018) 2 Z. Kang, S.-T. Lee Nanoscale 11, 19214 (2019) 3 K Holà et al. ACS Nano 2017, 11, 12402 4 N. Kholmicheva et al. Nanophotonics 8, 0143.

Resume : Single-walled carbon nanotubes (SWCNTs) are one dimensional (1D) nanocylinders consisting of rolled-up single graphene with the diameter of ca. 1 nm and the length of a few hundred nm or ~micro meter.[1] The cylindrical structures are identified by chiral indices that determine their diameters and properties, such as metallic and semiconducting features. In SWCNTs, the effects of quantum confinement and weak dielectric screening strongly appear in Coulombic interactions for carriers, and, therefore, stable excitons (electron–hole bound states) even at room temperature are generated by photoexcitation and emit photoluminescence (PL) in near infrared (NIR) regions.[2] Local chemical functionalization of the SWCNTs has been found to enhance their NIR PL properties due to its defect doping effect.[3-6] In the locally functionalized SWCNTs (lf-SWCNTs), chemical bonding between modifier molecules and nanotube walls forms defects such as sp3 carbon in their crystalline sp2 carbon networks. As a result, the defect doped sites emit E11* PL that is red-shifted and bright compared to the original E11 PL from pristine SWCNTs. That is due to narrow bandgap formation and exciton trapping (localization) function by the functionalization-induced electronic structure changes at the doped sites. In particular, the functionalized molecules on the doped sites play important roles for the wavelength modulation of E11* PL from the lf-SWCNTs.[3,4] For example, our proximal defect doping approach using bis-aryldiazonium salts allows to create largely red-shifted PL (E11^2* PL) over 1250 nm-regions from the lf-SWCNTs with (6,5) chiral index.[7,8] Molecular recognition designs at the doped sites achieve NIR sensing of sugar molecules[9], metal ions[10], etc. Recent studies for PL solvatochromism of lf-SWCNTs reveal that excitonic properties of localized exactions at the doped sites are effectively modulated depending on chemical structure differences of doped sites in lf-SWCNTs.[11,12] Therefore, defect engineering based on the molecular functionalization for lf-SWCNTs is a powerful tool for NIR PL modulation, by which advanced optical applications such as high performance bio/medical imaging and sensing using NIR II windows and photonic nanodevices for quantum communication would be developed. [1] S. Iijima, T. Ichihashi, Nature 1993, 363, 603; [2] Y. Miyauchi, J. Mater. Chem. C 2013, 1, 6499; [3] T. Shiraki, Chem. Lett. 2021, 50, 397; [4] T. Shiraki et al., Acc. Chem. Res. 2020, 53, 1846; [5] Y. Wang et al., Nat. Rev. Chem. 2019, 3, 375; [6] D. Janas, Mater. Horiz. 2020, 7, 2860; [7] T. Shiraki et al., Sci. Rep. 2016, 6, 28393; [8] T. Shiraki, et al., Chem. Lett. 2019, 48, 791; [9] T. Shiraki et al., Chem. Commun. 2016, 52, 12972; [10] T. Shiraki et al., Chem. Eur. J. 2018, 24, 9393; [11] T. Shiraki et al., Chem. Commun. 2019, 55, 3662; [12] T. Shiraki et al., J. Phys. Chem. C 2021, 125, 12758.

Resume : We present here field emission (FE) properties of two types of nanostructured composite films, promising novel materials for third generation electron sources and displays: (i) Nano-particle decorated multi-walled carbon nanotubes (MWCNTs)-and (ii) metal-insulator nano-composite thin-films. FE measurements were carried out in an indigenously developed high vacuum diode set up. The salient results obtained can be summarized as (i) a significant im-provement of FE current and temporal stability associated with an appreciable reduction in turn-on field from metal nanoparticle decorated MWCNT-films as compared to only MWCNT films: showing promises for electron-guns, x-ray sources etc.; (ii) appreciable increase in FE current density with high mechanical durability in metal nanoparticle decorated composites: promising planar emitter for future flat-displays. The enhanced FE characteristics of these emitters are understood from a combined experimental results, electronic structure and DFT based calculation.

Resume : Fostering the enormous potential of nanomaterials requires assembling them as organized structures on a macroscopic scale. For 1D nanomaterials a natural embodiment is as aligned fibres or fabrics that efficiently exploit the axial properties of their constituents. This talk describes a method to produce macroscopic solids made of 1D nanostructured directly collected as they grow floating in the gas phase. The strategy consists in synthesising 1D nanostructures suspended in a gas stream using an aerosol of catalyst nanoparticles, i.e. via floating catalyst chemical vapour deposition (FCCVD). Under this synthesis mode, growth is ultrafast, around 1000 faster than in substrate-based processes. The resulting high aspect ratio (> 200) enables the aggregation of nanomaterials in the gas phase and ultimately the formation of network solids. The talk reviews the use of this synthetic route to produce different nanotubes (e.g. carbon nanotubes – CNTs) and nanowires (SiNW). It analyses the factors that control the different possible reaction path in FCCVD and introduces a basic kinetic model to rationalise aspects of the reaction inferred from analysis of the nanostructures. Finally, the talk shows that some of these macroscopic ensembles behave as “macromolecular” networks with many superior properties compared to monolithic materials: fibres of carbon nanotubes have tensile mechanical properties above many high-performance polymer fibres; fabrics of CNTs are ideal built-in porous current collectors to eliminate electron resistance limitations in composite battery electrodes, sheets of silicon nanowires are flexible and have high cyclability as lithium-ion battery anodes.

Resume : The dielectric/electric properties of the Ni@C (carbon-coated Ni)/epoxy composites and Ni@C/MWCNTs (multi-walled carbon nanotubes)/epoxy composites loaded with fixed MWCNTs amount just below the percolation threshold (0.09 vol.%) and Ni@C at different concentrations up to 1 vol.% were investigated in broad frequency (20 Hz–40 GHz) and temperature (30 K–500 K) regions. In composites with the only Ni@C nanoparticles the electrical percolation threshold was determined between 10 and 15 vol.%. Above the percolation threshold the dielectric permittivity (ε') and the electrical conductivity (σ) of the composites loaded with Ni@C only are high enough, i.e. ε'=105 and σ=0.6 S/m at 100 Hz for composites with 30 vol.% Ni@C, to be used for electromagnetic shielding applications. The annealing to 500 K was proved to be an effective and simple tool to decrease the percolation threshold in epoxy/Ni@C composites. For hybrid composites series an optimal concentration of Ni@C (0.2 vol.%) was determined, leading to the conductivity absolute values several orders of magnitude higher than that of a composite filled with MWCNTs only. The synergy effects of using both fillers have been discussed. Below the room temperature the electrical transport is mainly governed by epoxy resin compression in all composites, while the electron tunneling was observed only in hybrid composites below 200 K. At higher temperatures (above 400 K), in addition to the nanoparticles redistribution effects, the electrical conductivity of epoxy resin makes a significant contribution to the total composite conductivity. The dielectric relaxation spectroscopy allows estimating the nanoparticles distributions in polymer matrix and could be used as the non-destructive and fast alternate to microscopy techniques for general polymer composite fabrication control.

Resume : Reduced graphene oxide has become a reliable material for sensing applications due to possessing properties such as large surface area, high electrical conductivity and ability to interact with various chemical species. Heavy metals bind with proteins and pose a potential risk to human life when exposed to higher concentrations. Thus, precise and quick detection of heavy metals is essential. Here, we report the use of β-cyclodextrin (BCD) functionalized reduced graphene oxide (rGO) as a chemiresistive sensor material for heavy metals sensing in the aqueous medium. Functionalization of rGO led to selectivity towards lead (Pb(II)) detection. A significant change in resistivity was observed within 15 minutes when the BCD functionalized rGO film was exposed to Pb(NO3)2 solution of various concentrations. A chemiresistive device was fabricated and characterized. The development of simple and selective chemiresistive sensors is expected to provide a facile solution for heavy metal detection for point of use sensing devices.

Resume : Carbon Atomic Wires are attracting increasing interest as they are the one-dimensional allotropic form of carbon, featuring outstanding mechanical, optical and electronical properties. [1] Carbon Atomic Wires consist in linear chains of sp-hybridized carbon atoms and exhibit two possible isomeric configurations: cumulenes (sequence of double bonds) and polyynes (sequence of single and triple alternated bonds). To date, only a few experimental studies have investigated their electronic properties in solid-state devices and they have focused mainly on molecular junctions or monolayers. Herein, we demonstrate that cumulenic Carbon Atomic Wires own great potential as organic semiconductors for solution-processed thin-film electronics. We report on the first example of organic field-effect-transistor (FET) based on short cumulenes molecular crystals, namely tetraphenylbutatriene [3]Ph. [2] Furthermore, we discuss on our latest achievements in understanding and optimizing charge-transport properties in solution processed thin films of these molecules. In particular, we show how to control the deposition of large-area thin-films of [3]Ph via wire-bar coating, a scalable printing technique, and achieve field-effect-mobilities up to 0.1 cm2V-1s-1. An in-depth characterisation of films obtained with different processing parameters allow us to correlate microstructural and morphological features with the FETs electrical performance. Lastly, our [3]Ph-based transistors provide excellent operational stability in dark conditions, therefore addressing one of the major concerns for the application of Carbon Atomic Wires, and in general of organic semiconductors, in ambient conditions. These results pave the way to the use of cumulenes as active material for organic electronics and open new possibilities for the chemical design of performant organic semiconductors based on sp-hybridised molecules. [1] C. S. Casari, M. Tommasini, R. R. Tykwinski and A. Milani, Nanoscale 8 (8), 4414−4435, (2016). [2] A. D. Scaccabarozzi, A. Milani, S. Peggiani, S. Pecorario, B. Sun, R. R. Tykwinski, M. Caironi, and C. S. Casari, J. Phys. Chem. Lett. 11, 1970−1974, (2020).

Resume : Nanomaterials have attracted widespread attention due to their tunable physical and chemical properties with enhanced performance over their bulk counterparts. The manipulation of matter at the nanoscale has opened enormous possibilities to meet challenges in different scientific and technological fields like optoelectronics, sensing, medicine, energy sustainability and engineering of new functional devices. Due to the exciting nature of nanostructures, nowadays, there is an increasing demand towards low-cost, effective and versatile nanofabrication methods. In particular, research efforts are focused on laser-based techniques for the growth and fabrication of nanostructures. In fact, laser-based techniques are simple and environmentally friendly and, in addition, with these methods is possible to control size, shape and composition of the materials being manufactured. In this talk, an overview of three different laser based techniques for the fabrication of different nanostructures, nanocomposites and thin films will be given.

Resume : The Luminescent Solar Concentrator (LSC) was originally introduced over four decades ago, as a potential alternative to Si solar cells. Since then, the LSC concept has evolved quite significantly, finding an ever-expanding application space, [1]. This is owed to the LSC's highly desirable inherent ability to efficiently concentrate incident light, even if diffuse, making it an extremely versatile and powerful photonic technology platform. Conventionally, optical systems are limited by the principle of conservation of étendue, meaning that there is a trade-off between the acceptance angle and maximum concentration gain that can be achieved. However, in the presence of Stokes shift, etendue needs not to be conserved in the same way: both broad acceptance angles and high concentration gains that grow exponentially with Stokes shift can be achieved, while still adhering to the second law of thermodynamics. Taking advantage of the above property and the potential high optical gains, luminescent solar concentrators have recently emerged as a promising receiver technology in free-space optical communications. Several high-speed communication systems integrating LSCs in their detector blocks have already been demonstrated, with the majority of efforts so far being devoted to maximising the received optical power and the system?s field-of-view. However, LSCs may pose a severe bottleneck on the bandwidth of such communication channels due to the comparably slow timescale of the fluorescence events involved, a situation further aggravated by the inherent reabsorption in these systems, and yet, an in-depth study into such dynamic effects remains absent in the field. To fill this gap, we have developed a comprehensive analytical solution that delineates the fundamental bandwidth limits of LSCs as optical detectors in arbitrary free-space optical links, and establishes their equivalence with simple RC low-pass electrical circuits, [2]. Furthermore, we demonstrate a time-domain Monte Carlo simulation platform, an indispensable tool in the multiparameter optimisation of LSC-based receiver systems. Our work offers vital insight into LSC system dynamic behaviour and paves the way to evaluate the technology for a wide range of applications, including visible light communications, high-speed video recording, and real-time biological imaging, to name a few. [1]. Papakonstantinou, I., Portnoi, M., & Debije, M. G. ?The Hidden Potential of Luminescent Solar Concentrators?. Adv. Energy Mater., 11, 2002883, 2020. [2]. Portnoi, M., Haigh, P. A., Macdonald, T. J., Ambroz, F., Parkin, I. P., Darwazeh, I., & Papakonstantinou, I. (2021). ?Bandwidth Limits of Luminescent Solar Concentrators as Detectors in Free-Space Optical Communication Systems?. Light: Science & Applications, 10(3), 2021.

Resume : In recent years, there has been an exponential growth of research activities in the production of new and more efficient photovoltaic (PV) devices. One strategy to enhance the efficiency of PV devices is to collect the radiation energy outside the absorption range of the photoactive material (usually silicon) by shifting its energy to a more suitable optical region. This energy conversion could be actuated by up-conversion (UC) or down-conversion (DC) luminescent materials. The energy converter system consists of a host material doped with light-emitting active species. One of the most efficient material for energy conversion processes consist of alkaline earth fluoride matrices, such as CaF2 and NaLnF4 (Ln:Y,Gd), appropriately doped with Ln3+ ions, such as Eu3+, Yb3+- Er3+ and Yb3+- Tm3+. In addition, these systems are promising materials as phosphors in other technological applications as biomedical assays and for micro and nanoscale thermometry, due to the direct connection between temperature and luminescent behavior of emitting doping. However, most of these applications require the luminescent material in form of thin films. In the present study, we report the synthesis of Ln-doped fluoride thin films starting from fluorinated metalorganic β-diketonate compounds, through two different chemical approaches: Metal Organic Chemical Vapor Deposition (MOCVD) technique and a combined sol-gel/ spin-coating method. The former has the advantage of being a very reliable and reproducible method for the fast production of films with high uniformity degree over large areas; the latter has the potential advantage of being a tunable and a potential scaling up method for the production of different kind of films homogenous in thickness and composition. A systematic study of both synthetic routes has been carried out to optimize the Ln doped CaF2 and NaMF4 (M:Y,Gd) films through an accurate control of the process parameters. In addition, for the synthesis of β-NaYF4 nanostructured thin films, two different precursor sources have been tested: i) a mixture of β-diketonate ‘‘second generation’’ Na(hfa)•tetraglyme and Y(hfa)3•diglyme complexes; ii) the novel fluorinated “third-generation” bimetallic compound NaY(hfa)4tetraglyme, which acts as single precursor for the metal components and the fluorine. The doping ions are introduced in the materials using the RE(hfa)3•diglyme complexes (RE = Yb, Er, Eu). The synthesized films have been characterized though X-ray diffraction to determine their structure, field-emission scanning electron microscopy for their morphology and energy dispersive X-ray analyses to determine their composition. Finally, spectroscopic properties in the visible and near infrared regions upon laser excitation at 980 nm have been investigated.

Resume : Supercapacitors are considered as a well-established energy storage device which is currently used in digital communication equipment, electric vehicle, regenerative braking systems, and voltage stabilization. Although the market of supercapacitors is growing rapidly due to their considerable capabilities including high power density, excellent low-temperature performance, fast charge/discharge rates, relatively lower costs, longer operational life, and environmental friendliness, their low energy density compared to batteries leads to a major barrier for the future of this technology. Therefore, preparing novel materials with higher power densities is critical for potential supercapacitor electrodes. One of the most important factors to control a supercapacitor's performance is the structure and properties of the electrodes. Porous nanocomposite carbon-based materials have been viewed for electrode materials of electrochemical cells due to their high surface area, large pore volume, and unique pore size distribution. Nevertheless, they suffer from low specific capacitance and low energy density which make them a good candidate to composite with metal oxide. By combining the carbon-based materials and metal oxide, the achieved composite has demonstrated larger external surface areas, high electrical conductivity, high capacitance, high energy and power density, and excellent cycle stability In this research, mesoporous carbon-based materials will be prepared by hard-templating and soft-templating methods. The metal oxide will be obtained via the hydrothermal method. Finally, for the characterization of the obtained structures, electrochemical techniques will be used to investigate electrochemical and supercapacitive characteristics of the composites.

Resume : Copper(I) complexes are one of the most promising ionic transition metal complexes (iTMCs) towards low-cost and sustainable lighting devices due to their optimal photophysical features and Cu abundance. Since 1970s[1] the photophysical behavior of copper (I) complexes with two chelating diimine ligands (N^N) have widely been investigated. In general, the emissive properties of the heteroleptic family [Cu(P^P)(N^N)][PF6] are far much better than those of the respective homoleptic family [Cu(N^N)2][PF6]. In addition, they often show thermal repopulation of the emitting singlet excited state from the lowest-lying triplet excited state, i.e., thermally activated delayed fluorescence (TADF) emission mechanism, allowing 100% electron harvesting. Up to date, single-layer Cu-iTMCs-based light-emitting electrochemical cells (LECs) can be driven at very low voltage reaching bright emission covering the visible spectrum; though white devices are still missing.[2,3] Herein, we have synthetized and characterized two novel blue-emitting heteroleptic [Cu(P^P)(N^N)][PF6] (λem=490 nm with ϕ= 40%). The corresponding LECs devices featured blue electroluminescence, achieving the best efficacy (3.6 cd A-1) reported up to date. In addition, they were blended with a previously published red-emitting Cu-iTMC,[4] realizing white-emitting devices with luminances of 30 cd m-2 and efficiencies of 0.6 cd A-1. The electroluminescence spectra corresponded to a white light output with x/y Commission Internationale de l’Éclairage 1931 (CIE) color coordinates of 0.29/0.35 associated to a color correlated temperature (CCT) of ca. 7400 K. So far, we reported the most stable and efficient fully copper(I)-based white-emitting LEC. Contextually, the two complexes have been investigated in detail through a joint theoretical and experimental investigation. Overall, this work pinpoints how critical the complex architecture is towards the design of highly efficient TADF LECs based on copper(I) complexes and the reported results constitute an important milestone toward sustainable and highly performing white-emitting LECs. References [1] D. R. McMillin et al., Inorg. Chem, 16, 943. (1977) [2] M.D. Weber et al., Dalton Trans., 45, 8984. (2016) [3] E. Fresta et al., J. Mater. Chem. C, 5, 5643-5675 (2017) [4] E. Fresta et al., Adv. Opt. Mater., 7, 1-11 (2019)

Resume : Recently, biomimetic polymers, specifically Polydopamine (PDA), have shown enhanced photocatalytic performance when combined with photoactive materials such as ZnO, TiO2, ZnS, among others. This talk presents recent developments and challenges of PDA/Semiconductor materials, covering the advances in PDA films from the air/water interface, nanocomposites and leading applications in energy production and water remediation[1-3]. Acknowledgements: National Science Centre (NCN) of Poland by the OPUS grant 2019/35/B/ST5/00248 Refernences: [1] Y. Kim, et al, Appl. Catal. B Environ. 2021, 280, 119423. [2] E. Coy, et al, ACS Appl. Mater. Interfaces 2021, acsami.1c02483. [3] D. Aguilar-Ferrer, J et al, Catal. Today 2021.

Resume : With the coming of the 4th Industrial Revolution, represented by Artificial intelligence (AI), Internet of Things (IoT), and Big-data processing, the demand of the new computing scheme for numerous data processing with less energy consumption in a short period of time has been rapidly increased. The conventional von Neumann computing architecture which is separating logic and memory blocks faced the challenge of the extensive power consumption and time delay by serial computing to transfer data between each block. A neuromorphic computing that mimics human brain functionalities has been considered that can overcome the limitation of von Neumann-based computing systems with its characteristics of parallel computing capability with energy-efficient data processing. From an energy efficiency point of view at the neuromorphic system, many candidates for synaptic devices have been suggested such as phase-change memory, resistive change memory, conductive bridge memory, and ferroelectric memory. However, it is still challenging to implement low power neuromorphic system with these emerging memories since more switching power reduction should be realized for parallel array application. Among the aforementioned applications, the ferroelectric device is one of the promising candidates for synaptic devices due to its low power and fast switching characteristics. In this work, we investigated the ferroelectric synaptic device based on metal-ferro-metal (MFM) structure using polyvinylidenefluoride-trifluoroethylene (P(VDF-TrFE)) copolymer. We fabricated MFM capacitors with respect to various PVDF weight percents, PVDF / TrFE composition ratio, and thickness of the ferroelectric polymer. Each sample’s ferroelectric characteristics e.g. coercive field, remnant polarization, and hysteresis were evaluated. Additionally, the synaptic plasticity characteristics such as long-term potentiation and long-term depression (LTP/LTD), and spike-timing-dependent plasticity (STDP) were thoroughly examined with each MFM capacitor. With these efforts, we could analyze the relation between ferroelectric switching properties and synaptic plasticity characteristics.

Resume : The modulation of single-walled carbon nanotube (SWCNT) photoluminescence has been under investigation for the unique potential to develop biosensors to detect many classes of analytes. Covalent sp3 defects on SWCNTs, sometimes dubbed organic color centers (OCCs) or carbon color centers (CCCs) have been explored for their photoluminescent properties, including the potential for introducing new emission bands, increasing quantum yield, and introducing new chemical sensitivities. The application of OCCs for biomedical applications requires new methods to both conduct covalent chemistry and to concomitantly control the surface chemistry and the resulting biological interactions/biocompatibility via their supramolecular interactions with polymers and other excipients. We have found specific utilities of OCCs for the detection of chemical phenomena where SWCNT photoluminescence is normally relatively insensitive, such pH changes in the physiologic range of 4.5 - 8. We have developed OCCs to measure endolysosomal pH in live cells and in vivo, as well as other emerging applications. We believe that OCCs will facilitate the development of biosensors for disease detection and biomedical research.

Resume : Low-pressure (1 Pa) plasma-based Magnetron Sputter (MS) deposition of metal targets onto liquids allows obtaining dispersions of small spherical nanoparticles (NPs). The main advantages of the method are its reproducibility and high purity of the final NPs. Indeed, only two components – target material and liquid molecules – are present in the solution, and no additional reducing or stabilizing reagents are required. Despite magnetron sputtering onto liquids has been studied since 1996, the mechanism of NP formation is still not fully understood. To provide more insight on this topic, sputtering of gold, silver, and copper targets onto vacuum-sustaing castor oil, rapeseed oil, and its polymers has been systematically studied. The effects of sputtering time, sputter power, argon gas pressure, type of sputtering plasma (Direct Current Magnetron Sputtering (DC-MS) vs High-Power Impulse Magnetron Sputtering (HiPIMS)), and viscosity of host liquid onto NP properties have been studied experimentally and by quantum-chemistry calculations. Moreover, in situ temperature measurements have allowed us to better understand how the heating of the liquid during the plasma treatment affects the formation of NPs. Magnetron sputtering of gold, silver, and copper targets leads to the formation of a dense cloud of particles underneath the oil surface which can be easily homogenized by mechanical stirring but films are formed in the case of high-viscosity oils. Gold NPs have higher stability in castor oil solutions than silver NPs, but secondary growth processes take place. Copper NPs rapidly oxidize due to reaction with oil molecules, inducing the formation of intermediate compound between copper and oil components and, finaly, the growth of copper oxide NPs. According to TEM the diameters of primary NPs obtained with the DC-MS plasma are in the range of 2.4 – 3.2 nm for gold, 0.8 – 4.0 nm for silver, and 2 – 4 nm for copper oxide. Depositions in HiPIMS mode allow the formation of NPs almost twice bigger in case of gold and silver. Moreover, applying a bipolar HiPIMS power supply leads to the formation of larger aggregated NPs which is discussed in terms of liquid heating and kinetic energies of the sputtered species.

Resume : In recent years, the fabrication of laser-generated surface structures on metals such as titanium surfaces have gained remarkable interests, being technologically relevant for applications in optics, medicine, fluid transport, tribology, and wetting of surfaces. The morphology of these structures, and so their chemistry, is influenced by the different laser processing parameters such as the laser fluence, wavelength, pulse repetition rate, laser light polarization type and direction, angle of incidence, and the effective number of laser pulses per beam spot area. However, the characterization of the different surface structures can be difficult because of constraints regarding the analytical information from both depth and the topographic artifacts which may limit the lateral and depth resolution of elemental distributions as well as their proper quantification. A promising technique to investigate these structures even at the nano-scale is Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), a very surface sensitive technique that at the same time allows to perform depth-profiling, imaging and 3D-reconstruction of selected ion-sputter fragment distributions on the surface. In this study we combine chemical analyses such as Energy Dispersive X-ray spectroscopy (EDX) and high-resolution scanning electron microscopy (SEM) analyses with ToF-SIMS to fully characterize the evolution of various types of laser-generated micro- and nanostructures formed on Ti and Ti alloys at different laser fluence levels, effective number of pulses and at different pulse repetition rates (1 – 400 kHz), following irradiation by near-infrared ultrashort laser pulses (925 fs, 1030 nm) in air environment or under argon gas flow. We show how this combined surface analytical approach allows to evaluate alteration in the surface chemistry of the laser-generated surface structures depending on the laser processing parameters and the ambient environment.

Resume : Molecular Doping (MD) is a technique in which dopant-containing molecules, used as a dopant source, are deposited on top of a semiconductor and diffused inside it through a drive-in process. Every phase of the MD process represents a step onto which subsequent phases will build upon to obtain the final doped sample, so an in-depth study of each phase will improve the control on the electrical properties of the final doped samples. Hence, studying the chemical bonds forming during the deposition step between the molecules becomes an essential aspect to be studied. It is already known from the literature1 that the molecules form a self-assembled monolayer over the semiconductor, but little is known on the possible multiple layers forming on top after prolonged deposition times. To this end, we performed high-resolution morphological analyses to investigate the molecular surface coverage at different timestamps and examined the effect of the surface treatments on it. To gain deeper theoretical insight on the bonding nature, we pair these analyses with density functional theory simulations, as an extension of the previous study2, and with electrical measurements of the final doped samples. We find information on the type of chemical bonds forming between the several layers of molecules and how they impact the doping profile. This will allow for a more precise tuning of the electrical properties of MD-based devices. 1 S. Caccamo et al., Materials Science in Semiconductor Processing 42, 200-20 (2016) 2 Puglisi, R.A., et al. Direct observation of single organic molecules grafted on the surface of a silicon nanowire. Sci Rep 9, 5647 (2019).

Resume : Over the last decade, the transition from conventional vacuum based thin film deposition techniques to solution processes has remarkably empowered the evolution of a novel manufacturing scheme. Besides time and cost-efficiency included in their major advantages, solution processes additionally present an outstanding compatibility with a plethora of materials. Amongst them, metal oxides (MOs) constitute an attractive research field, as their significantly enhanced optoelectronic properties, concomitantly with high optical transparency and mechanical stability render them as highly promising. ?Sol-gel? is established as one of the currently favourable solution processes, as it uniquely links metal oxides to solution processing. This deposition of organometallic precursors via wet techniques, followed by a subsequent thermal treatment, prevails the formation of high-quality metal oxides, while accommodating essential advantages such as ambient processing conditions and composition tuning. However, these advantages may simultaneously constitute challenging manufacturing points. This, coupled with a high demand on ultra-thin films (< 10 nm) in IC industry, constitutes the presence of high-sensitivity characterization techniques as essential in sol-gel industry. So far, well-established methods such as XPS and TEM have been widely used in sol gel research. However, their cost and time-consuming nature hinders their implementation in a high-throughput production line. In addition, their ?destructive? character restricts the possibility of in situ monitoring during fabrication. Therefore, the presence of non-invasive, highly-sensitive characterization techniques could introduce a remarkable upgrade of sol gel research and industry. To address this challenge, we propose Infra-Red Spectroscopic Ellipsometry as an alternative and novel approach towards the clarification of the sol gel precursor conversion stages, the control of which leads to high quality metal oxide ultra-thin films. Particular focus is being paid in the role of substrates, as their tuning may enhance the detection of spectral features, thus allowing the detection of vibrational modes in ultra-thin films (~ 1 nm). In this study, In(NO3)3 dissolved in 2-Methoxyethanol (C3H8O2) is conversed into an ultra-thin In2O3 film (< 10 nm), a widely popular metal oxide semiconductor. The individual stages are captured by IRSE, aiming to shed light into the sol gel reaction conversion. For this, various substrates are being utilized (Al, TiN, Au and Si), aiming to enhance the IRSE sensitivity, thus provide a clear monitoring of the conversion process through vibrational mode detection. We thus identify the intermediate products during transition towards In2O3. This introduces IRSE as a new route towards the detection of sol-gel stages in ultra-thin films, with its implementation in solution processing technologies being potentially essential. The substrate effect is further reinforcing the importance of IRSE in thin film industry, as it potentially covers an expanded material palette, such as 2-D materials.

Resume : In recent years, lanthanide metal-organic frameworks (Ln-MOF) have displayed interesting properties making them appealing for various applications. The use of lanthanide elements as dopants within MOF’s structures leads to the acquirement of unique luminescent properties, which can be exploited for the fabrication of optical sensors. Up to now, different Ln-MOFs have been studied for the detection of toxic ions, heavy metals, and small molecules. The special feature of these materials refers to the capability of tailoring their properties by simply changing their internal structure, through variation of the organic linkers and the metallic centre or by modifying the operating conditions such as time, temperature and pressure. So far, the scientific community has focused great attention on the development of new and environmentally friendly strategies for the synthesis of Ln-MOF to obtain more and more complex structures with the best properties, but having at the same time a low environmental impact. The most recent applied strategy for the syntheses of Ln-MOFs is the solvothermal reaction which uses organic solvents, high pressure and very long reaction times. The challenge in the development of more sustainable synthetic strategies actually leads to the exploration of new and greener approaches. In this context, we propose a one-step synthesis under mild conditions of Eu doped Ln-MOF (Ln = Gd, Y, Tb) in water/ethanol solvents. The use of 1,3,5-benzenetricarboxylic acid (H3BTC) as the organic ligand and Ln(NO3)∙nH2O as a source of Y, Tb and Eu results in the formation of Y,Eu-BTC and Tb,Eu-BTC. The Gd-MOF and Eu-doped Gd-MOF is formed by using the ditopic 1,4-benzenedicarboxylic acid (H2-BDC) linker, yielding respectively Gd-BDC and Gd,Eu-BDC networks. The obtained powders were characterised by X-ray diffraction (XRD), FT-IR spectroscopy and field emission scanning electron microscopy (FE-SEM) for the investigation of structure and morphology. Finally, preliminary studies were performed in order to investigate the luminescent properties of Ln-MOF doped with Eu ions, specifically Gd-BDC and Gd,Eu-BDC MOFs have been applied to the sensing of Fe3+ and Cr2O72-.

Resume : Carbon Nanodots (CDs) are carbon nanoparticles characterized by intense and tunable absorption-emission in the visible range 1. Their optical response is combined with a great sensitivity to external agents2. Besides, CDs display exceptional electron donating capabilities, interesting for several applications2, 3. The combination of all of these characteristics promisingly projects the use of CDs as suitable substitutes of quantum dots in many optoelectronic or photo/electro-catalysis applications. Single-wall Carbon Nanotubes (SWCNTs) are probably one of the most iconic materials in nanoscience, endowed with a range of exceptional properties ultimately related to their 1D structure 4. By decorating the surface of CNTs with various functional groups or molecules5, it is possible to increase their colloidal stability, and to prepare them for coupling to other nanomaterials, such as CDs. Here, we synthesized nanocomposites of CDs + CNTs, and studied their interactions by the synergy of different structural and optical techniques, supported by DFT investigations. Their successful coupling is directly shown by HRTEM measurements and demonstrated by optical methods: the photoluminescence of CDs is quenched when they form complexes with nanotubes, indicating a strong electronic coupling. This interpretation is confirmed by ultrafast transient absorption spectroscopy, which directly highlights a very fast electron transfer (<60 fs) followed by a slower back electron transfer ( 60 ps) from the nanotube to the carbon dots. The reported results pave the way to use these "all-carbon" nanocomposites as efficient light harvesters for applications in artificial photocatalysis and photosynthesis. 1. Sciortino, A. et al. C-Journal of Carbon Research 2018, 4 (4), 35. 2. Zu, F. L.et al. Microchimica Acta 2017, 184 (7), 1899-1914. 3. Arcudi, F. et al. Angewandte Chemie-International Edition 2017, 56 (40), 12097-12101. 4. Rahman, G. et al. C-Journal of Carbon Research 2019, 5 (1), 31. 5. Tasis, D. et al. Chemical Reviews 2006, 106 (3), 1105-1136.

Resume : Absorption of the solar radiation over a wide spectral range is of an utmost importance to applications related to the harvesting of the solar energy. We numerically as well as experimentally demonstrate broadband solar absorption enhancement employing a metamaterial in the form of arrays composed of subwavelength silicon truncated inverted cones, henceforth referred to as light funnel (LF) arrays. Light trapping in arrays composed of subwavelength light funnel arrays (LF arrays) is a promising approach towards efficient broadband absorption of the solar radiation. In the following we examine the origin of light trapping enhancement in LF arrays as compared to nanopillar (NP) arrays and we show that light trapping enhancement is due to favorable strong optical coupling between adjacent light funnels which is not realized in NP. We suggest that the enhanced light trapping and absorption in dense LF arrays is governed by strong modal excitation coupled with high filling ratio, unlike the absorption in dense optimized nanopillar arrays which is governed by weak modal excitation and high filling ratio. In this current study optical near-field of LF and NP arrays has been explored experimentally using near-field optical microscopy. We show that in LF arrays the near-field increases as the array period decreases in contrast with NP arrays in which the near-field decreases with decreasing array period. Therefore, it is suggested that the origin to the broadband absorption in compact LF arrays is due to field overlap of adjacent LFs which increases the absorption cross-section of the individual LFs composing the array. This enhancement in the absorption cross section and the higher filling ratio in compact arrays produce broadband absorption that is significantly higher than that of optically-optimized NP arrays.

Resume : Silicon nitride thin films are promised as a good candidate for anti-reflection coatings and third-generation quantum dot-based solar cells1,2. Variation in the stoichiometry (x = [N]/[Si]) of a-SiNx:H can regulate different optical properties of the material, making it suitable for different optoelectronic devices. SHI irradiation, annealing and other treatments can alter various properties of a-SiNx:H by changing the hydrogen content and density of thin films. SHI irradiation is widely accepted as a desirable technique for modification and change in properties of thin films and nanostructures embedded in different matrices. Singh et al. reported in-situ agglomeration of excess Si into Si nanostructures in host silicon nitride matrix. For swift heavy ion irradiationat lower fluences, a dissolution of Si nanostructures was observed, whereas the further increase in fluence resulted in the formation of amorphous Si nanostructures3.The origin of latent ion tracks microstructure evolution and changesin amorphous SiNx upon SHI irradiation at various fluences was also observed4,5. These results show different structural evolution in SiNx thin films upon irradiation. The different evolution can be understood in terms of stoichiometry and its effect on ion material interaction.The present work reports the effect of SHI irradiation on sub-stoichiometric a-SiNx:H thin film on their properties. Thin films of different stoichiometry (x = 1.42 to Si-rich x = 0.17) were irradiated with various fluences of 100 MeV Au8+ ions. The various properties of as-deposited and SHI irradiated a-SiNx:H films are explored in detail.The out-diffusion of Hydrogen due to irradiation is quantified with the help of ERDA.RBS was probed to study the change in thin films’ composition upon irradiation, which further helps understand the change in thin films’ optical properties. Quenching of photoluminescence in the films with all stoichiometries was also observed due to ion irradiation. X-TEM images show the formation of discontinuous ion tracks of radius 2.5 nm in the film closer to silicon nitride stoichiometry. However, Si rich film does not show the clear formation of tracks. Results are explained in the framework of the Thermal spike mechanism of ion-solid interaction. The observation ofthe discontinuous ion track-like structures upon swift heavy ion irradiation is explained on the basisof a dynamic electronic energy loss in the course of irradiation resulting fromthe out-diffusion of Hydrogen from the thin films and a continuous increase in density ofa-SiNx:H. References: 1 J. Schmidt and M. Kerr, Sol. Energy Mater. Sol. Cells 65, 585 (2001). 2 H.K. Raut, V.A. Ganesh, A.S. Nair, and S. Ramakrishna, Energy Environ. Sci. 4, 3779 (2011). 3 S.P. Singh, S. Ghosh, G. Vijaya Prakash, S.A. Khan, D. Kanjilal, A.K. Srivastava, H. Srivastava, and P. Srivastava, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 276, 51 (2012). 4 L.A. Vlasukova, F.F. Komarov, V.N. Yuvchenko, V.A. Skuratov, A.Y. Didyk, and D. V. Plyakinc, in Bull. Russ. Acad. Sci. Phys. (2010), pp. 206–208. 5 R.K. Bommali, S. Ghosh, G. Vijaya Prakash, D. Kanjilal, P. Mondal, A.K. Srivastava, P. Srivastava, R.K. Bommali, D. Kanjilal, S. Ghosh, A.K. Srivastava, P. Mondal, and G.V. Prakash, Mater. Res. Express 2, 46204 (2015).