Materials for nanoelectronics and nanophotonics

Resume : The fields of photonics and plasmonics have generated a long-standing interest, only accelerated in the past two decades due to advances in nanoscale fabrication and characterization. The optical response of different materials highly depends on the materials' optical properties, dimensions, and surroundings. These relations can be complex to understand for researchers getting into the subject and for experienced researchers who intend to examine and evaluate the impact of subtle differences in the material models while setting up experiments or getting a general overview. The Photonic Materials Cloud (PMCloud) [1] is a web-based, interactive tool for comparing optical material models from a database, experimental data input, and inline-generated materials, using various methods, including Drude-Lorentz parameters. PMCloud provides a fully interactive interface to assign materials, compare their subtle optical differences, and evaluate their performance in important (numerical) photonic experiments, such as the scattering by core-shell nanoparticles and multi-layer thin-film devices. This talk will introduce the PMClouds and demonstrate its applicability to state-of-the-art research questions, such as comparing novel plasmonic materials to classical metals like gold and silver and designing optical, dielectric, and metallic thin-film devices. PMCloud opens up a free and fast path to prototyping optical materials and simple fundamental devices, and it can serve as an educational platform for photonic materials research. [1] http://photonicmaterials.eu

Resume : CaF2 is a well-known FCC crystal with an ultra-wide band gap (~11.8 eV) and a relatively high dielectric constant (~8.43). The considerable progress achieved recently in MBE-grown tunnel-thin CaF2 layers makes it a possible gate insulator in FETs and dielectric in MIM devices [1]. The accurate determination of structural and electronic properties of CaF2 in bulk and low dimensional system is therefore of crucial importance. Traditional DFT methods are known to suffer from severe band gap underestimation. The GW [2] methods can correct this band gap error but are costly. The hybrid functional calculations like the screened exchange (sX) [3] or HSE functionals are less time-consuming, but the addition of Hartree-Fock (HF) exchange can cause a divergence at the Fermi energy with metallic systems. The GGA U method, which introduces the Hubbard parameter U to treat the electron-electron repulsion is useful to treat metal-semiconductor systems where hybrid functionals diverge due to the HF terms. However, introducing the U term in HfO2 led to an over-estimate of the electron affinity, although not in MgO. Here we test the GGA U method for a similar ionic system. Here, we compare the detailed CaF2 band gap structure calculated with different schemes considering its seriously underestimated large band gap using GGA. The sX results predict an indirect gap (X−Γ) of 11.78 eV, well consistent with the experiment value of 11.80 eV [4]. The GGA U with U=9.5 eV on F p states can also effectively correct the band gap to 11.11 eV. We note that different methods tend to position the band edges differently, so we specially consider the ionization potential (IP) of bulk CaF2 to validate the accuracy of different schemes. The calculated IP values 11.55 eV (sX) and 10.71 eV (GGA U) agree well with the experimental 11.96 eV [4]. Our results present an overall description of the electronic structures of CaF2, and act as supplement to the understanding of the accuracy of the GGA U. We further apply the low cost GGA U method at the technologically important CaF2/Si interfaces. Our supercell calculations show obvious type-II band alignment with a 1.76 eV CBO for the (111) orientation, which is normally obtained during epitaxial growth of CaF2 on the silicon substrate [5]. The interface band aligmnment reported here is in good agreement with the experimental characterisation. [1] G. Wang, et al, J. Am. Chem. Soc. 131, 14200 (2009); G. Chen, et al, ACS Nano 6, 8280 (2012). [2] T. Bischoff, et al, Phys. Rev. B 101, 235302 (2020). [3] S. J. Clark, et al, Phys. Rev. B 82, 085208 (2010); Miyoung Kim, et al, Appl. Phys. Lett. 84, 3579 (2004) [4] G. W. Rubloff, Phys. Rev. B 5, 662 (1972); R. T. Poole, et al, Chem. Phys. Lett. 36, 401 (1975). [5] M. A. Olmstead, et al, Phys. Rev. B 35, 7526 (1987)

Resume : The concept of magnetron sputtering systems is not fully studied in an analytical form. This is related, e. g., to the current-voltage characteristic, the equation of which allows only a qualitative interpretation. In addition to the complexity caused by the physical processes of the gas discharge and currents in none-homogeneous electric and magnetic fields, difficulties in describing magnetron spraying processes are associated with the design features of the technology setup and its geometry. The setup for magnetron deposition of thin films was designed and manufactured. In particular, this unit was tested for the deposition of ZnSnN2 nanometric layers for detector and photovoltaic applications. The studies of the kinetics of charge transport in magnetron spray systems was performed based on the continuity equation, Ohm's law and Poisson's equation. It has been theoretically found that the current-voltage characteristics of a DC magnetron system depend as a square function on three parameters, one of those being equal to the ignition potential in gas discharge, the other two are being determined by using the experimental curves for low / high applied voltages as a function of the magnetic field, the gas pressure, the geometric dimensions and the physical concept of the setup. The theoretical results obtained are in correlation with the experimental data for the ZnSnN2 films deposited by reactive magnetron sputtering on various substrates (glass, quartz, Si), being further structurally (GI-XRD) and morphologically (AFM, STM) characterized. Acknowledgements: NARD (ANCD) project: 20.80009.5007.12

Resume : The strong coupling regime of light-matter interaction attracts significant attention due to its possibility of utilization in energy harvesting, nonlinear optics and the possibility to modify material-related properties or chemical reactions. Plasmonic nanostructures, due to their large cross section for interaction with light, can act as very efficient optical antennas even when small in size and can are of great interest for hot carriers generation. While light absorption in metal particles is efficient, they are characterized by short lifetime of hot carriers. However, by coupling to a nearby molecule the hot carriers can be utilized to perform useful work, what is studied here in a strongly coupled plasmon-molecule system. To study hot carrier generation and evolution in a strongly coupled system we consider a magnesium nanoparticle interacting with small molecules of 2-(4H-cyclopenta [2,1-b:3,4-b']dithiophen-4-ylidene)malononitrile (CPDT). In this work, we use a computational quantum study based on time-dependent density-functional theory approach to access the physics of nanoscale nanoparticle-molecule assemblies and predict vacuum Rabi splitting. We analyse nanoscale polaritons generated in small nanoparticle-molecule systems to obtain coherent femtosecond dynamics of photon absorption, plasmon formation, and subsequent hot-carrier generation. We predict the energetic and spatial hot-carrier distributions in nanoparticle-molecule systems and reveal the impact of strong coupling on the hot carrier distribution. According to these results, we reveal how hot carriers could be tailored by the strong coupling of nanoparticle-molecule systems. The plasmonic systems with strong coupling of electronic and photonics states make them promising candidates for nanoelectronic and optoelectronic applications.

Resume : Chirality is a molecule or structure property that is present in our daily life, it can be from nano (conformation of small molecules) to macro (our hands or the shape of galaxies). Generally, enantiomers show similar physical properties, however, normally they have opposite optical properties, how they are able to rotate the plane of polarization of an incident beam light. When an electromagnetic beam interacts with plasmonic nanoparticles, this generates a localized surface plasmon resonance (LSPR) with highly intense electromagnetic field at nanoparticles surface. Coupling the LSPR of achiral structures with chiral molecules, it is possible to increase and modify the chiroptical response of the hybrid nanomaterial. Chiral plasmonic nanostructures have been developed by assembly achiral plasmonic nanoparticles into chiral configurations by using chiral templates or chiral molecules.1 Recently, plasmonic nanoparticles with an intrinsic chirality have been achieved.2,3 In this context, we have developed one step synthesis of chiral-plasmonic nanoparticles by using achiral gold nanorods as seeds. We have studied the chirality evolution by HR-TEM as well as the chiral efficiency. Likewise, depending on the seed used, we are able to control and tune the CD response of the new chiral nanoparticles. Thanks to the layer by layer technique we have deposited on a glass substrate different layers of chiral nanoparticles and the chiroptical response have been evaluated. Moreover, taking advantage of the CD better efficiency than the LSPR, we have used the chiral substrates to developed a more efficient system to measure the refractive index sensitivity. References: (1) Guerrero-Martínez A., et al. Intense optical activity from three-Dimensional chiral ordering of plasmonic nanoantennas. Angewandte Chemie. 2011, 50 (24), 5499-5503 (2) Hye-Eun L., et al. Amino-acid and peptide-directed synthesis of chiral plasmonic gold nanoparticles. Nature 2018, 556, 360–365. (3) González-Rubio G., et al. Micelle-directed chiral seeded growth on anisotropic gold nanocrystals. Science. 2020, 368, 1472-1477

Resume : In recent years, beta-Ga2O3 micro-/nanostructures have exhibited technological potential in many device applications, such as field-effect transistors, photodetectors, gas sensors, solar cells, and nanophotonic switches. Nanotubes or nanowires have been successfully grown using various materials and have received attention due to their mesoscopic phases, which provide new physical properties and strong applications for devices. Although efforts have been made to fabricate beta-Ga2O3 micro-/nanotube. The beta-Ga2O3 micro-/nanotube reported were mostly disordered or inclined. The synthesis of large-scale growth of beta-Ga2O3 tubular structure arrays with uniform morphology is still a huge challenge. At present, the inductively coupled plasma (ICP) etching technology for the preparation of GaN nanowire (NW) arrays is mature, but there are few reports on the preparation of ?-Ga2O3 NW arrays by ICP etching [Ding, S.; Zhang, L.; Li, Y.; Xiu, X.; Xie, Z.; Tao, T.; Liu, B.; Chen, P.; Zhang, R.; Zheng, Y. A Selective Etching Route for Large-Scale Fabrication of beta-Ga2O3 Micro-/Nanotube Arrays. Nanomaterials 2021, 11, 3327. https://doi.org/10.3390/ nano11123327 Academic E] [Young Chul Choi, Won Seok Kim, Young Soo Park, Seung Mi Lee, Dong Jae Bae, Young Hee Lee, Gyeong-Su Park, Won Bong Choi, Nae Sung Lee, and Jong Min Kim Catalytic Growth of beta-Ga2O3 Nanowires by Arc Discharge, Adv. Mater. 2000, 12, No. 10]. Comprehensive understanding of the role of the structural morphology of an array of ?-Ga2O3 nanotubes in the development of the electronic properties of such arrays is required. The work is devoted to the properties of the electron subsystem of model array of nanotubes (or nanowires) formed by fibers of beta-Ga2O3. The main research methods are theoretical calculations based on the density functional theory and the ab initio pseudopotential method. Using author?s software [http://sites.google.com/a/kdpu.edu.ua/calculationphysics], the spatial distribution of valence electron density, the distribution of electron states density, the Coulomb potential along the vector in the array, effective charges on atoms were calculated. The effect of the geometric parameters of the arrangement of nanotubes in an array and their diameters on the electronic properties of an array of nanotubes is determined. One of the investigated arrays of nanotubes was with such parameters, namely, the diameter was 6.75 angstroms, and the height was 15.7 angstroms. The nanotubes were arranged relative to each other with respect to square symmetry. The substrate for holding an array of wires is not taken into account. The interaction between the tubes is manifested starting from the distance between them in 4.7 angstroms, and is characterized by the following parameters: the magnitude of the band gap was 31.5 eV, the Coulomb potential in the region between the wires was near zero in relative unit. Whereas at a distance between the tubes equal to 0.7 angstroms, when the exchange of electron density between the wires was clearly fixed, these parameters were: the band gap was 2.1 eV, the Coulomb potential in the region between the tubes was 15.4 relative units.

Resume : MoS2; a 2D TMDC has attracted immense attention in energy storage devices, optoelectronic devices, optical switching devices, and gas sensors due to its unique physical and chemical properties. MoS2 thin films and nanostructures can be synthesized by different physical and chemical growth mechanisms. CVD is one of the most effective methods to achieve large-area growth of atomically thin horizontal and vertical 2D TMDCs for device applications. The vertically aligned MoS2 nanostructures are reported to have maximum edge sites, reactive dangling bonds, and high adsorption-desorption capacity, making them an attractive candidate for gas sensing. In CVD the growth conditions such as the temperature of the heating zone, growth duration, the pressure inside the tube, and the carrier gas flow rate are tuned to change the alignment and number of layers of MoS2 thin films. In this work growth parameters such as temperature, Mo:S ratio, source to substrate position, and growth time have been optimized for synthesizing few-layered vertically aligned MoS2 thin films through a one-step CVD process. The formation of MoS2 thin film was confirmed by the presence of E_2g^1 and A_1g peaks in the Raman spectra. The presence of an intense (002) peak in the XRD pattern further indicates the formation of MoS2 thin film. FESEM and TEM images show an obvious evolution from horizontal to vertical morphology of MoS2 nanoflakes with a growth condition. The vertical morphology, provides a high rate of adsorption and desorption processes and outstanding gas sensing properties due to the presence of dangling bonds and higher aspect ratio. Herein, few-layered vertically aligned MoS2 nanoflakes were obtained directly on Si/SiO2 substrate supported with interdigital Au electrodes were used for gas sensing measurement. The fabricated MoS2 sensor shows response towards H2S at room temperature. However, sensors fabricated from 2D TMDCs suffered sluggish response and recovery time. Therefore to prevent homogeneous restacking and enlarge the active surface area 2D/2D heterostructure was developed by decorating MoS2 nanoflake on Si/SiO2 with 1T/2H MoS2. These 2D / 2D heterostructure-based gas sensors showed enhanced response and sensitivity towards H2S sensing at room temperature and the architecture can be considered for developing efficient gas sensors.

Resume : Thick-film performance of ceramics based on the mixed NiMn2O4-CuMn2O4-MnCo2O4 system has a number of advantages over other types of functional electroceramics, especially in combination with layers of humidity-sensitive nanostructured Mg?-Al2O3 ceramics. In this case, one more important task arises: transformation of all the functional properties of bulk materials in a layered and integrated multifunctional thick-film implementation in order to further miniature device applications. The aim of this work is fabrication and characterization of structural properties of temperature- and humidity-sensitive thick-film nanostructures. Thick-film temperature-sensitive elements and multilayered structures based on Cu0,1Ni0,8Co0,2Mn1,9O4 with p-type electrical conductivity, Cu0,1Ni0,1Co1,6Mn1,2O4 with ?+- type of electrical conductivity and dielectric Mg?-Al2O3 (i-type) were investigated. The humidity-sensitive thick-film layer was applied to pre-formed temperature-sensitive layer. It should be noted that formation of p-?+, p-?+?, thick-film structures and integrated temperature-humidity-sensitive p-?-?+ structures was carried out within one technological cycle. The Cu0.1Ni0.8Co0.2Mn1.9O4 thick films on the Rubalit substrate consist three phases. There are diffraction lines of the spinel phase, aluminum oxide from the substrate and a low intensity line from a solid solution (Ni1-xMnx)O based on a NiO phase with a NaCl cubic structure. The presence of Bi2O3 as in the previous case, was not detected. As for the Cu0,1Ni0,8Co0,2Mn1,9O4 sample, an amorphous halo is observed at the angle of 20-33° 2?, which arises due to the technical limitations of X-ray imaging for the object of this form and due to diffraction from the material of cuvette. It is established that the Mg?-Al2O3 thick films on Rubalit substrate contain two phases - a spinel and an aluminum oxide from a substrate. Bi2O3 reflexes were also not detected, indicating their amorphous state. In accordance with results of topological investigations thickness of temperature-sensible ?- and ?+-layers was 43.75 ?m and 46.88 ?m, accordingly. The of two-layered ?+-? thick-film structure is 139.06 ?m, ?+-? ? 110.16 ?m, and integrated p-?-p+ thick-film structures with conductive Ag layer ? 193.73 ?m (thickness of Ag layer is 45.31 ?m). It is shown structure of humidity-sensitive thick films is especially expressly selected on a background of Al2O3 substrate with conductive Ag layer. Evidently, that material contains the far of shallow pores, which serve as ducting for the receipt of water to nanopores, where processes of capillary condensation takes place, and also macropores which provide the effective receipt of water in the inner structure of material from an environment. In contrast to microstructure of humidity-sensitive Mg?-Al2O3 thick films, Cu0,1Ni0,8Co0,2Mn1,9O4 thick films contain a greater amount of macropores formed in clusters. A similar structure is also characteristic for bulk material of the same composition. Thus, the structural features of ceramics can be transformed into thick films of similar compositions.The use of ceramic with a spinel structure as the main output component for preparation of thick films provided the density of the multi-layer structure and the component for the production of thick films, provided the density of the multi-level structure and contact of their layers.

Resume : The mechanism of radiative recombination and emission of ZnO nanorods and the effect of Au nanoparticle (20 nm in size) decoration on the luminescence properties are studied. ZnO nanorods (100 nm wide, 700 nm long) were synthesized by chemical bath deposition while decoration with small Au nanoparticles (density of 1010 nanoparticles/cm2) was achieved by immersing the sample in a colloidal solution of nanoparticles. The decoration of this metal oxide with noble metal nanoparticles has been quantitatively investigated by Scanning Electron Microscopy and Rutherford Backscattering Spectrometry, while the emission properties of the bare and decorated samples have been studied by photo- and cathodo-luminescence. Radiative recombination mechanism has been studied through depth-resolved cathodoluminescence analyses (supported by Montecarlo simulations), while generation, diffusion, and recombination of electron-hole pairs below the surface has been deeply investigated and simulated. The combination of ZnO nanorods and Au nanoparticles causes a significant depletion of free electrons below the surface, leading to a reduction of UV emission and an increase of visible-UV intensity ratio. The formation of a nano-Schottky (modelled with a multiphysics approach) leads to a relevant bending of ZnO energy bands, evidencing a strong electric field beneath the metal-semiconductor interface which affects the emission [1]. The depletion of free carriers in decorated ZnO nanorods allows the application of these composite materials in UV sensing and light induced catalysis. [1] Bruno, L.; Strano, V.; Scuderi, M.; Franzò, G.; Priolo, F.; Mirabella, S. Localized Energy Band Bending in ZnO Nanorods Decorated with Au Nanoparticles. Nanomaterials 2021, 11, 2718. https://doi.org/10.3390/nano11102718

Resume : Nanomaterial fabrication in the desired compact form is the most important prerequisite for scientific and technological development. Nowadays, the key challenge is to design the nanomaterial in 3D complex forms equipped with the proper functions and simultaneously easy to utilize. Their extensive applications in healthcare, aerospace, automotive, electronic, smart polymers, smart textile, sensors, medicine, etc., make it essential to study and research this young novel technology. ZnO tetrapods provide exclusive advantages because they can be used as a unique building block to construct a high porous interconnected network in the form of flexible ceramics. Additionally, these tetrapods can be used as backbones to deposit a new material on their top in the form of hybrid tetrapodal materials. This work introduces a novel single-step approach to fabricate composite materials based on ZnO tetrapods. This new method offers advantages such as industrial scalability and cost-effectiveness. In addition, no harsh chemicals are used in this method. Furthermore, the ZnO-based 3D interconnected network can be hybridized with a wide range of metals and metal oxides, e.g., copper oxide, cobalt oxide, iron oxide, nickel oxide, titanium oxide, cerium oxide, platinum, silver, gold, antimony, etc. by this method.

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 a Pt interdigitated electrode. XRD analysis confirms the hexagonal crystal structure of nanorods. The chemoresistive behavior is investigated in the 250-400°C temperature range and the 2000-50000 ppm range of H2 concentrations. The measured response transients have been successfully modeled within the Langmuir theory by hypothesizing two independent active processes: a fast process (below 4 s) which is attributed to the 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 the development of fast, sensitive, and low-temperature operating H2 sensors based on WO3. [1] Mineo, G., Moulaee, K., Neri, G., Mirabella, S., & Bruno, E. (2021). H2 detection mechanism in chemoresistive sensor based on low-cost synthesized WO3 nanorods. Sensors and Actuators B: Chemical, 348, 130704.

Resume : Nanocrystals of intermetallic compounds are a large family of emerging materials with highly promising electronic, plasmonic, catalytic, magnetic, and energy storage applications. However, generalized synthetic approaches for intermetallic nanocrystals are lacking. Here we report the development of a colloidal synthesis based on amalgamation of monometallic nanocrystal seeds with low-melting metals. [1] We use this approach to achieve crystalline and compositionally uniform intermetallic nanocrystals of Au-Ga, Ag-Ga, Cu-Ga, Ni-Ga, Pd-Ga, Pd-In and Pd-Zn compounds. Furthermore, we demonstrate a compositional tunability across phase diagrams (e.g., AuGa2, AuGa, Au7Ga2, and Ga-doped Au nanocrystals for the bimetallic Au-Ga system), while each phase can be prepared with accurate size control and excellent size uniformity. Our new synthetic method is simple, predictive, and generalizable, giving access to a large family of intermetallic nanocrystals with unprecedented quality and flexibility of materials design, thus unlocking a multitude of possibilities for these materials. [1] J. Clarysse, A. Moser, O. Yarema, V. Wood, and M. Yarema, Science Advances, 2021, 7, eabg1934.

Resume : In the emerging area of research on optoelectronics, investigators are currently focused on hybrid nanostructures of cost-effective, non-toxic and earth-abundant materials for device fabrication due to their versatile physio-chemical properties which are completely different from bulk. In this work, we explore the possibility of incorporating noble metal and bimetallic nanoparticles (Ag/Au/Ag-Au) into tin monosulfide (SnS) semiconducting thin films for their potential application in an extended wavelength range of photodetection. Recently, the field of hybrid nanostructures of semiconductors and plasmonic materials has expanded tremendously owing to the improvement in performance of semiconductor devices by taking advantage of the strong light/matter interaction of the plasmonic nanomaterials. Nanocolloids of SnS, Ag, Au and Ag-Au are prepared in isopropyl alcohol (IPA) by pulsed laser ablation in liquid (PLAL) technique using a Nd:YAG laser of wavelength 532 nm. The hybrid thin films are fabricated by depositing these colloids onto glass substrates using an ultrasonic spray deposition technique. The structure, morphology and optical properties are analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-Vis-NIR spectrophotometer. A comparison of the photodetector performance of nanostructured SnS hybrid films of Ag, Au, Ag-Au will be carried out. The photodetection of the films in the UV-Vis-NIR region will be evaluated by sensing their response to illumination sources operating in the wavelength range from ~200 to 1000 nm. The results of photodetector parameters such as photosensitivity, responsivity, detectivity, rise time and decay time will be presented. This work demonstrates the versatility of PLAL technique in combining the plasmonic and semiconducting properties of nanomaterials and opens a new synthetic entryway for combination of other nanoparticles as well.

Resume : Ultra-thin and extra-large single-crystalline Au micro-flakes (Au MFs) have a huge potential for applications ranging from nanophotonics to nanoelectronics. Yet, wet chemical-synthesis approaches cannot access this size range due to the proportionality between growth time, thickness and lateral size. Concurrently, complexity and small MFs areas restrict the use of 2D template-based methods. In all case, subsequent transfer to a substrate remain challenging. Here, we demonstrate a facile, gap-assisted synthesis method that enables on-substrate growth of ultra-thin and extra-large Au MFs. In particular, using a 43 μm gap-size between two glass substrates and leveraging the directed-growth effect of halide ions, we achieve a high yield (~90%) of Au MFs on glass with lateral sizes as high as 0.25 mm and thicknesses as low as 10 nm. Interestingly, up to 25h growth-time we observe a time-independent, ultra-low average thickness of just 21 nm. A parametric synthesis study and an in-depth material characterization provide mechanistic insights into this extreme 2D growth mode. Overall, our gap-assisted approach greatly enhances the halide effect and results in a record-high aspect-ratio of ~10^4. It thus opens new opportunities for on-substrate anisotropic growth strategies that would benefit emerging optoelectronic and photoelectrochemical devices.

Resume : Behavior of palladium and platinum nanofilms 100 nm thickness deposited onto oxide materials during annealing in vacuum was investigated in this work. These nanofilms were applied by electron beam method on polished surfaces of substrates from quartz glass, leucosapphire, ceramics based on Al2O3 and ZrO2. Samples with films applied to them were annealed in vacuum not worse than 2x10-3 Pa during for different time (2 ? 20 min) and at different temperatures (1000 up to 1600 ?°). The study found that in the process of annealing in vacuum, platinum and palladium nanofilms deposited onto quartz glass substrate are rapidly dispersed on individual fragments and droplets and after annealing at 1300 ?C completely disintegrate, covering a small area of the substrate surface, and also interacts with quartz glass. Therefore, for soldering quartz glass, these films are not suitable as metallizing materials. Palladium nanofilm deposited onto leucosapphire rapidly disintegrate during annealing, exposing more than 70% of the substrate surface area in the first minutes of annealing at 1200 °C. Platinum nanofilm onto leucosapphire during annealing, in contrast to palladium nanofilm, disintegrate much more slowly and at higher temperatures. Since at annealing temperatures up to 1300 ?C platinum nanofilm covers almost 60% of the leucosapphire surface area even at long exposures at these temperatures, it can be recommended for metallization of leucosapphire detales for further soldering at temperatures up to 1300 ?C. The behavior of platinum and palladium nanpfilms onto alumina ceramics during annealing is very similar to the behavior of these films onto leucosapphire. Palladium film also disintegrate rapidly during annealing, exposing more than 65% of the substrate surface area in the first minutes of annealing at 1200 °C. Platinum nanofilm during annealing at 1300 ?C covers almost 65% of the substrate surface with exposure to 20 min. Thus, since at annealing temperatures at 1300 °C platinum nanofilm covers 60% of leucosapphire and 65% of alumina ceramics surface area even at long exposures at this temperature, platinum nanofilm can be recommended for metallization of leucosapphire and alumina ceramics deatails for further soldering at 1300 °C. Platinum film deposited onto zirconia ceramics during annealing at temperature 1100 ? 1200 °C covers about 50% of zirconia ceramics surface area at exposures up to 10 min, so it can be recommended for metallization of zirconia ceramics details for soldering at temperatures up to 1200 °C. According to the results of research, the kinetic curves of the dispersion process during the annealing of platinum and palladium nanocoatings onto oxide materials surfaces are plotted and recommendations are given for the practical application of these coatings for joining of metallized oxide materials.

Resume : The vapor-liquid-solid technique, used for growing silicon nanowires (SiNWs), requires a metallic liquid particle to catalyze silicon precursors dissociation. Catalyst selection is a critical step as it has a direct impact on the SiNW morphology. Single element catalysts are the norm, but new properties can be achieved with bi-element catalysts. However, the growth mechanisms involving complex catalysts remain unclear. Experiments in plasma-enhanced chemical deposition reactors show that such catalysts can yield wires with very small diameters and metastable phases [1]. In this work, we use bimetallic Cu-Sn particles and a hydrogen atom source to perform the in situ growth of SiNWs in a transmission electron microscope (TEM) [2]. This combination of two metals gives rise to the liquid-assisted vapor-solid-solid (LA-VSS) growth mode where the catalyst particle at the SiNW tip has both a liquid Sn-rich and a solid Cu3Si domain. Both phases work in tandem to yield small diameter SiNWs in a step-flow fashion. Through the use of a high-frequency camera, we find the nucleation site of a new planes to be along the interface separating the solid and liquid part of the catalyst. The new nucleus then grows laterally, first in the liquid and finally in the solid, at different velocities. By varying the deposited Cu/Sn ratio, we can fine tune the wires growth direction, twin density, and tapering angle. Thus, the LA-VSS technique provides an original bottom-up pathway for controlling nanowires features, especially in very small ones. Such catalysts are also instrumental in forming the metastable hexagonal-diamond (2H) phase, predicted to have unique electronic and optical properties [3]. We find that nano-size effects stabilize this phase, as it is found exclusively in small SiNWs (13 % of below 5 nm diameter NWs have the hexagonal phase) [1,2]. [1] W. Wang et al., ACS Omega 6, 40, 26381-26390 (2021) [2] E. Ngo et al., J. Phys. Chem. C 125, 36, 19773-19779 (2021) [3] M. Amato et al., Nano Lett. 16, 5694-5700 (2016) [4] We thank F. Panciera and U. Mirsaidov for providing substrates allowing zone-axis growth. Work supported by the French National Research Agency through the TEMPOS Equipex, pole NanoMAX (ANR-10-EQPX-50) and HexaNW project (ANR-17-CE09-0011).

Resume : Two phenylated phosphine ligands, diphenylmethylphosphine (DPMP) and triphenylphosphine (TPP), were incorporated onto cesium lead bromoiodide nanocrystals (CsPbBrI2 NCs) to improve air stability in the ambient atmosphere. The incorporation of DPMP and TPP ligands was also verified to enhance film-forming and optoelectronic properties of the CsPbBrI2 NCs. The experimental results reveal that DPMP is a better ligand to stabilize the emission of CsPbBrI2 NCs than TPP after 21 days storage. The increased carrier lifetime and PLQY of perovskite NCs was observed due to the surface passivation by DPMP or TPP ligands, reducing non-radiative recombination at the trap sites. The DPMP and TPP-treated CsPbBrI2 NCs were successfully utilized as the red emitter for fabricating perovskite light emitting diodes with enhanced performance and prolonged device lifetime relative to the pristine perovskite NCs.

Resume : The halide perovskites ABX3 (X: Cl, Br or I) are useful for photovoltaic or light-emitting devices due to their favourable optical properties of a direct bandgap and strong optical absorption just above the bandgap. Wuttig et al [1] recently proposed an unusual model of their multisite metavalent bonding involving the p-orbitals of the Pb and halogen sites of the BX3 framework, compared to the usual covalent bonding of the typical optical semiconductors. The model explains the low effective electron and hole masses based on a simple model of their band structure. Here, by first-principle calculations, we show that the strength of the optical absorption arises from an increase in the transition matrix element [2], [3] to one bond length, twice the normal value. The transition probability between the valence and conduction bands is increased to four times higher than the normal value. These lead to a very sharp increase in the optical absorption or Urbach tail [4]. Analysis of the bonding in these compounds shows that the B-X bonds have about 50% ionic bonds and 50% covalent bonds, while the A-X bonds have almost fully ionic bonds. This bonding mechanism is unique to 3D halide perovskites compared to oxide perovskites and 2D halide perovskites. Discussions in this report provide essential guidance to design better optical materials. [1] M Wuttig, et al. Adv Func Mats 32 2110166 (2021) [2] W Harrison, et al. Phys Rev B 14 691 (1976) [3] W Jackson, et al. Phys Rev B 31.5187 (1985) [4] C M Sutter-Fella, et al. ACS Energy Letts 2 709 (2017).

Resume : Investigations on the perovskite-inspired cesium bismuth iodide (Cs3Bi2I9) as a potential candidate to meet the toxicity and stability issues of hybrid lead halide perovskites have identified a wide range of its optoelectronic applications. Cs3Bi2I9 single crystals have displayed attractive performance in photodetection, especially as excellent hard radiation detectors. Besides, self-powered photodetectors that can operate without any power consumption to give reliable electrical signals by converting light are suitable for environmental monitoring, territory intrusions, light-wave communication and imaging technology. In the present work, we develop lead-free Cs3Bi2I9 films by ultrasonic spray deposition at substrate temperatures ranging from 150 to 400 ℃. Uniform films with excellent substrate adhesion are investigated in detail using structural, morphological, compositional, optical and electrical characterization techniques. At substrate temperatures lower than 325 ℃, highly crystalline films with well-packed grains were obtained. In addition, the degradation of these films when grown at higher substrate temperatures is explained. The absorption coeffcients of the films were in the order of ~104 cm-1 and the direct band gaps calculated were in the range of 1.8 – 2.1 eV. All the films were photoconductive under the illumination of a 50 W halogen lamp. Furthermore, self-powered photodetection of Ag/FTO/Cs3Bi2I9/C-Ag structure is demonstrated under AM1.5 as well as 532 nm and 405 nm laser illuminations. For a 405 nm laser with light illumination of 7.08 mWcm-2 at 0 V, the responsivity and detectivity yielded were 5.08 × 10-6 AW-1 and 5.93 × 108 Jones, respectively. The rise time and decay time were respectively estimated as 1.52 and 2.29 s. Our results suggest that stable and reliable self-powered photodetectors can be developed based on sprayed Cs3Bi2I9 films in atmospheric conditions.

Resume : Metal halide perovskites (MHPs) have shown outstanding optical emissive properties and can be employed in several optoelectronics devices. In contrast with materials of well-established technologies, which are prone to degradation or require expensive processes, LHPs can be obtained by solution processing methods and increase stability. We propose inkjet printing as an industrial friendly technique to deposit LHPs. We have developed inks from colloidal CsPbBr3 nanocrystals and printing procedures that allow the deposition of thin layers with intense green emission. We proved that high emissive printed layers are assured by carrying out thermal annealing in vacuum oven, which is demonstrated to promote compact layers with low roughness, as corroborated by SEM and AFM. XRD measurements show CsPbBr3 crystalline layers with cubic symmetry and XPS provides insight into the stoichiometric composition and local bonding. Optical properties of inkjet-printed CsPbBr3 films have been analyzed by UV-vis absorbance and photoluminescence (PL), in order to extract the band gap energy and photoluminescence quantum yield (PLQY). CsPbBr3 printed layers emit at 524 nm with a narrow emission (FWHM ≈15 nm), exhibiting a PLQY up to 20 %. These results enabled the large-scale fabrication by inkjet printing of CsPbBr3 color conversion layers (CCLs) and pave the way for flexible LEDs.

Resume : Sunlight is the simplest renewable energy at our disposal. The transformation of this energy into another usable one (electric, chemical, …) needs to be optimized. It is particularly true in the case of photocatalysis where only a few % of the solar light is efficiently converted in the catalysis process. One way to overcome this limitation is by adapting the solar spectra to the photocatalyst by using upconversion materials capable of converting low energy photons into higher energy ones. This approach seems at first glance very interesting but many obstacles have to be overcome. In particular, the process is highly nonlinear and for instance to generate UV photons one generally needs 3 or more IR photons requiring a high excitation intensity (typically a few W/cm2), 2 to 3 orders of magnitudes higher than the solar irradiance. In order to optimize an upconverting material for photcatalysis applications we have developed an original synthesis method based on anhydrous precursor allowing to get bare nanoparticles with upconversion efficiencies equivalent to their bulk counterparts. In addition, by combining several beams with different excitation wavelengths, we demonstrate that the upconversion process becomes linear with respect to each excitation wavelength, thus paving the way for UV light generation under broadband and low intensity excitations such as broad solar-type excitation. For instance it is possible to generate 360nm photons from LiYF4:Yb3+,Tm3+ nanoparticles under an equivalent solar excitation.

Resume : Thanks to their properties of fluorescence emission in the near infrared region (NIR) and upconversion (UPC), the Er doped Y2O3 nanoparticles are excellent candidates for biological applications and, in particular, for bioimaging. Unlike traditional fluorophores, these lanthanide NPs do not exhibit photobleatching, phototoxicity and light scattering; moreover they are excellent probes for cathodoluminescence since their luminescence is not extinguished by electron beams. In this study we will focus on the synthesis, characterization and functionalization process in order to obtain water stable and biocompatible NPs for biological applications such as bioimaging and drug delivery.

Resume : This investigation is reported that Gd2O3:Tm3 , Er3 , Nd3 particles can be multifunctional identification markers, because combine luminescence and magnetic properties in one single particle. The information carriers based on oxide particles doped with group rare earth (REI) ions were synthesized using the standard Pechini method and a modified method with foaming components to produce weak particle agglomeration. Potassium carbonate has been identified as the optimum blowing agent for the synthesis of Gd2O3:REI according to a study of the structural properties, morphology and luminescence characteristics. The possibility of creating an identification code based on luminescent and magnetic parameters has also been demonstrated. The luminescent spectral code is based on the ratiometric approach and is formed from the relative intensities of non-overlapping luminescence lines of different types of ions. Magnetic parameters can also be an identifier as they are dependent on dopant atoms, dislocations in the crystal structure, etc. Thus, the idea of the coding system described is introduces a promising concept for safety markers. Acknowledgments: Authors are grateful to ?Interdisciplinary Resource Centre for Nanotechnology?, Resource Center "Innovative technologies of composite nanomaterials?, ?Research Centre for X-ray Diffraction Studies?, ?Centre for Optical and Laser Materials Research? and ?Centre for Diagnostics of Functional Materials for Medicine, Pharmacology and Nanoelectronics? of Saint-Petersburg State University Research Park. The authors are grateful to the Russian Science Foundation, project N? 20-79-00101.

Resume : Significant efforts have been made in recent years to produce novel functional materials for the manufacturing of increasingly complex and advanced photovoltaic devices (PV) that can guarantee effective use of the solar radiation. The conversion of photons with energies beyond the absorption range of the photoactive material (typically silicon) into a more appropriate optical area is an advanced strategy used to improve the efficiency of PV systems. Due to their distinctive luminous characteristics under light irradiation, lanthanide (Ln)-doped fluoride materials are seen as particularly promising for energy conversion (EC) applications. The EC mechanism may be accomplished by simply incorporating a material capable of hosting an active luminescent Ln element into the PV layers. The principal luminescence methods utilized for EC applications, which increase the efficiency of solar systems, are upconversion (UC), downconversion (DC), and downshifting (DS). Europium, among the other Ln elements, has piqued the scientific community's interest because of its unique chemical characteristics, particularly in the oxidation state +3. Fluorides have previously been shown to be more effective inorganic hosts for EC processes than other inorganic matrices. Because of its low phonon energy (similar to or even lower than commonly used hosts such as NaYF4), high chemical stability, wide transparency, and versatile synthetic strategies, BaF2 is considered a potential host for the incorporation of luminescent Ln3+ ions. However, it is essential to emphasize that host materials require Ln3+ dopant ion lattice matching, hence, because of their comparable coordination sphere, trivalent lanthanide ions may be easily integrated into the crystal structure of alkaline-earth fluorides. Nevertheless, to balance the increased charge created by replacing divalent alkaline-earth ions with trivalent Ln dopants, a charge compensation mechanism is necessary. In this research, we describe the fabrication of Eu-doped BaF2 thin films on various substrates utilizing the metalorganic chemical vapor deposition technique (MOCVD), with an emphasis on the manufacturing process and DS luminescent characteristics. A multicomponent combination of metalorganic adducts, in an acceptable molar ratio, is employed as a single molten source for the manufacture of BaF2 thin films doped with Eu3+. By modifying the composition of the precursor mixture, i.e. the Ba:Eu ratio in the multicomponent source, it is feasible to readily adjust the chemical compositions of the films and customize the energy transfer processes. The films were characterized structurally, morphologically, and compositionally using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray analysis (EDX). Finally, luminescence spectroscopy was used to evaluate the film functional properties.

Resume : Molybdenum oxides are versatile semiconductors whose optical and electronic properties depend strongly on their stoichiometry. In particular, MoO3 is transparent and shows a wide bandgap (>3 eV) and a high dielectric constant k ~ 500 [1]. Due to its unique optoelectronic properties has been used for the injection of holes in LEDs and photovoltaic solar cells, in gas sensors, in photochromic, thermochromic, and electrochromic effects devices among other applications [2]. However, due to its large bandgap this material does not exhibit luminescence in the visible. In this research, we study the doping of molybdenum trioxide (MoO3) nanostructured layers with nanoparticles of europium oxide (Eu2O3) to induce light emission. The synthesis of the MoO3 nanostructured films was carried out by a pulsed laser deposition (PLD) based process under the optimal conditions of pressure, temperature and thickness [3]. The deposited films are initially amorphous and upon annealing at 250ºC 2D orthorhombic MoO3 nanocrystals with slab shape are formed. In order to dope these nanocrystals, we have intercalated during the PLD growth Eu2O3 nanoparticles at different concentrations (1%, 3% and 5%). After the 250ºC annealing, it was observed that the Eu2O3 incorporation directly affected the formation of MoO3 nanocrystals: at high doping Eu concentration the MoO3 is inhibited, and only the films with the lower Eu doping concentrations (1%) showed formation of the 2D-MoO3 crystals. Photoluminescence spectra of the Eu-doped 2D-MoO3 show emission at 612 nm which is characteristic Eu3 5D0-7F2 transition due to the incorporation of the Eu in the orthorhombic 2D-MoO3 crystals structure. We will discuss the special properties of the luminescence emission in these nanocrystals. References: [1] Castro, et al. Adv. Mater. 1701619 (2017). [2] Puebla et al. Nanomaterials 10, 1272 (2020). [3] J. H. Kim, et al. 2D Mater. 6, 015016 (2019). Keywords: Molybdenum oxides, Eurpium, nanoparticles, photoluminescence, laser deposition

Resume : The possibility of synthesizing refractory luminescent materials in air in the field of powerful fluxes of hard radiation during one second without the introduction of additional substances to facilitate the formation of the phase was shown in [1, 2]. This paper presents for the first time the results of the studies of the excitation and luminescence spectra of ceramics based on alkaline earth metal fluorides, synthesized under an electron beam with an energy of 1.4 MeV and a flux power density of 22?25 kW/cm2. Samples of ceramics BaF2, MgF2, BaxMg2-xF4 (x=1, 0.5, 0.25, 0) were synthesized from a charge consisting of a mixture of industrial BaF2 and MgF2 powders in different ratios and tungsten trioxide powder in an amount of 1% of the total charge weight, as dopant. We studied both as-grown samples and synthesized samples annealed in air at a temperature of 750°C for 8 hours followed by slow cooling to 300 K. The synthesized samples are not transparent in the region above 3.4 eV. The photoluminescence excitation spectra of all materials are a set of bands at 3.5, 5, 5.63 eV. Upon excitation in each of the bands, luminescence appears in the region of 3.2?2.1 eV in the form of a wide monoband (FWHM ?1 eV) with the position of the maximum in the spectra of samples of various compositions in the range of 3?2.5 eV. The value of the characteristic decay time in BaxMg(2-x)F4 depends on the ratio between cations and decreases from 195 to 30 ?s when x changes in the range 1?0. Annealing of the synthesized samples is accompanied by a significant (by an order of magnitude) increase in the luminescence intensity. Consequently, at such a high rate and a sharp increase and decrease in the radiative forcing, the formation of the phase does not have time to complete. And post-radiation thermal annealing should be considered as a necessary condition for the completion of the synthesis process. Presented the RRD patterns of research samples. ?ne of the main advantages of the used synthesis method is the solving the problem with doping effective emission centers - polyvalent ions: W, U, Ti in the lattice of refractory materials. 1 Lisitsyn V.M. ?Nuclear Inst. and Methods in Physics Research B 435 (2018) 263?267 https://doi.org/10.1016/j.nimb.2017.11.012 2. Lisitsyn V.M. ?Russian Physics Journal, Vol. 61, no. 10, 1909-1913, 2019 DOI 10.1007/s11182-019-01617-y

Resume : This work reports on the optical properties of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy. Under an extremely low excitation density, the photoluminescence (PL) spectrum of the studied structure exhibits two emission sub-bands, named L and H. Different from that of the low-emitting band (L-band), a super-linear dependence is detected from the evolution of the integrated PL intensity of the high-emitting band as a function of the excitation density. From a comparative study between the optical results of a set of grown QD samples, the super-linear behavior has been related to the radiative emission from the first excited states of the dots. The study of the dependence on the excitation density of the linearity of the integrated PL intensities of the QD transitions made it possible to determine the real origin of the emission bands observable in the double-peak emission of an ensemble of InAs QDs. On the other hand, the PL measurements of the studied samples showed that the random process of capture of carriers by the dots could be the most relevant mechanism for the appearance of PL signals from the first-excited state emissions of the dots, even at very low excitation densities which correspond on average to less than one e-h pair per dot.

Resume : In this work, we investigate the effect of rare earth ions substitution on the structural, optical, and conduction behaviors of Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 (BCRETZN) (RE=Ce, Pr) compound ceramic produced via a solid-state route. The Rietveld analysis of the X-ray pattern at room temperature indicated a tetragonal structure (P4mm) of our compound ceramic. Afterward, the morphology of the ceramics was explored using scanning electronic microscope (SEM) as well as optical response and conduction behavior. The Photoluminescence properties revealed that the BCPrTZN sample gives rise to the green and red photoemissions under laser excitation at 450 nm at RT. Furthermore, for BCCeTZN sample, the photoluminescence spectra showed that strong violets emission bands were obtained, under excitation at 350 nm at RT The presence of Pr and Ce element in such materials may have significant technological promise in novel multifunctional devices.

Resume : Optical thermometry based on the luminescence intensity ratio has great potential in biomedical research, as it is a non-contact non-invasive thermal sensing technique, allowing to achieve high spatial resolution (typically < 1 µm2). The most promising materials found in the literature for the development of this technique are those doped with lanthanide ions. The Nd3+ and Yb3+ ions have a great advantage for in vivo application, as they operate (excitation and emission) within the biological transparency windows, a spectral range in which the main tissue constituents are transparent [1-3]. This work aims to develop novel nanothermometers doped with Nd3+ and Yb3+ with high thermal sensitivity (> 1%.°C-1) for in vivo application. First, due to its ease of synthesis and generic nature, the polymeric precursor method – modified Pechini method - was selected to produce nanopowders of several oxide phases in order to screen the thermometry properties: Y2O3, Y2Ge2O7, Y3Al5O12, Y3BO6, YBO3 and YAl3(BO3)4). Typically, the annealing conditions of the dry resins obtained by calcination under a controlled oxygen atmosphere were adjusted in time (between 3 and 10 min) and temperature (around 900-1100 °C), as evidenced by Differential Thermal Analysis (DTA), X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) to obtain nanocrystals. The luminescence signal of the different matrices, studied first in single Nd3 -doped samples, was found optimal between 0.25 and 1 mol% Nd3+ according to the crystal structure. Samples codoped with Nd3+ and Yb3+ were then synthesized according to the same procedure and their luminescence properties were measured, in particular at physiological temperature range (25-45°C), to assess their thermal sensitivity. The study of thermal sensitivity was done considering the luminescent intensity ratio between different emission lines and allowed us to understand the effects of cross-relaxation and lattice vibration involved in the temperature-dependent energy transfer process between the Nd3+ and Yb3+ doping ions. Then, after this screening, the compounds with the most promising thermal sensitivity were synthesized by solvothermal method to obtain individual nanocrystals that can be used for in vivo measurements [4]. Well-crystallized 50-nm sized Y3Al5O12 and larger YBO3 nanocrystals have been obtained under mild pressure (200 bar) and temperature (200-300°C). Thus, the first nanothermometry results obtained for these most promising phases will be presented. References 1- R. Galvão et al. Nano Select 2 (2021) 2, 346–56. DOI: 10.1002/nano.202000148. 2- G. Gao et al. Advanced Optical Materials (2021) 9, 2001901. DOI: 10.1002/adom.202001901. 3- K. He et al. Optical Materials (2021) 112, 110724. DOI: 10.1016/j.optmat.2020.110724. 4- G. Dantelle et al. RSC Advances (2018) 8, 26857-26870. DOI: 10.1039/c8ra05914d

Resume : In the quest for new and increasingly efficient photon sources, the design of the photonic environment at the subwavelength scale is fundamental for controlling the emitter optical properties. It is well known, indeed, that the spontaneous emission rate of an emitter can be modified acting on its electric and magnetic local density of optical states (LDOS). Recently, all-dielectric high refractive index nanostructures have attracted increasing interest due to their unique optical properties (i.e., low absorption, optical magnetism, and multipolar responses) that can be exploited to enhance the optical properties of a nearby emitter without decreasing its quantum efficiency. However, the relatively modest Q-factors exhibited by electric and magnetic Mie resonances (Q∼5-10) have limited the application of high-index nanoparticles in the enhancement of the LDOS. A possible way for obtaining orders of magnitude higher Q-factors in all-dielectric nanostructures is based on optical bound states in the continuum (BICs). Although true BIC can exist in structures that are infinitely extended at least in one direction, finite-size systems can support their analogue in the form of quasi-BICs, with the resonance quality factor that increases rapidly before reaching a maximum value limited by the finite-size effects. Despite the novelty of the field, q-BICs have already demonstrated their ability to outperform traditional photonic nanostructures for many photophysical processes usually limited either by losses or by low Q-factor resonances, such as second-and third-harmonic generation, light guiding, beam shaping, and sensing. Nonetheless, the realization of nanoantennas able to boost the emitter optical properties through an efficient coupling with q-BIC modes remains still an open issue. In this framework, we propose a novel design for the all-dielectric nanoantennas supporting quasi-BICs, with an ultrathin silicon oxide layer doped with erbium ions placed inside slotted silicon nanopillars arranged in a square array. We demonstrate that by coupling the Er3+ radiative emission at about λ=1540 nm with q-BIC resonances, 2 orders of magnitude decay rate enhancement and almost 3 orders of magnitude photoluminescence intensity increment have been measured at room temperature. Furthermore, acting on the nanoantenna aspect ratio, the emitter magnetic branching ratio can be tailored from 10% to 90%, keeping the quantum efficiency almost unitary. Finally, exploiting the reciprocity principle it was possible also to design and control the emission directivity from the nanoslot, focusing more than 90% of the Er3+ emitted radiation at λ=1540 nm in a lobe normal to the sample surface with an angular width of Δθ<10°. Hence, we have designed and realized CMOS compatible lossless nanoantennas able to boost the photon generation at telecom wavelength.

Resume : Rare-earth (RE) doped silica or silicon nanocrystals have attracted a lot of attention over the last few years due to their potential applications for applications in photonics. Light emission properties exhibited by Si-nanoclusters and RE are directly linked to the distribution of the dopants in the host materials and clustering characteristics (size, distribution, composition, interface nature with surrounding matrix…). Therefore, an accurate control of these parameters is essential in order to improve the optical properties of these systems. However, the solubility of rare earth ions in Si-based materials achieved is still relatively low and most of the RE ions are optically inactive at high concentration due to the formation of cluster. In this context, we have investigated highly doped Erbium silicon oxide layer elaborated by RF magnetron sputtering. The influence of the Er concentration and annealing process have been studied both on the optical properties by photo- and cathodo-luminescence and on the chemical and structural properties at the atomic scale by transmission electron microscopy and atom probe tomography. It is found that for high concentration of Erbium (up to 9 at.%), a decomposition of an Er-rich phase and Si-rich phases appears leading to the formation of two subnetworks in the film. The luminescence properties from UV to IR range will be discussed in regard to the chemistry of each phase according to the temperature annealing.

Resume : Fast, selective and low-cost nitric oxide (NO) sensors are highly needed due to the harmful effects of this gas. Low temperature NO detection is as requested as challenging, requiring selective and effective catalytic processes. Metal oxides (MOx) are most widely used materials for gas sensor applications [1]. Usually, n-type semiconductors require high operating temperature (>300°C) and have low sensitivities [2]. For this reason, p-type semiconductors have been extensively studied for gas sensors. Here, we present an experimentally based CuO-NO interaction model in the 50-400 °C temperature range and a promising NO detector working at 50°C based on CuO nanoparticles (NPs) realized by pulsed laser ablation in liquid environment (PLAL) technique. Ligand-free Cu/Cu2O nanostructures produced by PLAL in deionized water and were converted into CuO NPs by 400°C annealing, and analysed by X-Ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray techniques. A chemoresistive sensor is produced by drop-casting 0.1 mL of CuO NPs suspension onto an interdigitated electrode of Pt/Al2O3 and tested in a flow-controlled test chamber. Studying the sensor response toward several gas, the highest and fastest response toward NO is obtained at 50°C. It was observed that the resistance had an opposite behaviour fluxing NO at different temperatures. Below 250°C an oxidation behaviour is recorded while above 350°C reduction takes place, with a peculiar transient regime observed at 300°C. Hence, a full model of CuO-NO interaction based on Langmuir adsorption theory is proposed and kinetics barriers has been extracted by analysing the response curves in the 50-400 °C temperature range [3]. A peculiar catalytic activity of CuO NPs emerges in combination with oxygen species absorbed at different temperature, leading to effective NO detection. The ease and scalability of CuO NPs production by PLAL and the reported fast and selective NO sensor working at 50°C open promising routes towards exploitation for massive and affordable harmful gas detection. [1] R. Malik, V. K. Tomer, Y. K. Mishra and L. Lin, Functional gas sensing nanomaterials: A panoramic view, Applied Physics Reviews 2020, 7, 021301. https://doi.org/10.1063/1.5123479 [2] Hou, C. Zhang, L. Li, C. Du, X. Li, X. F. Kang, W. Chen, CO gas sensors based on p-type CuO nanotubes and CuO nanocubes: Morphology and surface structure effects on the sensing performance, Talanta 2018, 188, 41-49. https://doi.org/10.1016/j.talanta.2018.05.059 [3] M. Censabella, V. Iacono, A. Scandurra, K. Moulaee, G. Neri, F. Ruffino, S. Mirabella, Low temperature detection of nitric oxide by CuO nanoparticles synthesized by pulsed laser ablation. Submitted.

Resume : Here, we discuss the effect of In2O3 nanoparticles on the reduced graphene oxide (rGO) gas-sensing potentialities. In2O3 nanoparticles were prepared with the polymer precursors method, while the nanocomposites were prepared by mixing an In2O3 nanoparticle suspension with an rGO suspen-sion in different proportions. The gas-sensing performance of our materials was tested by exposing our materials to known concentrations of a target toxic gas in a dry airflow. Our results demonstrate that In2O3 nanoparticles enhance the rGO sensitivity for strong oxidizing species such as O3 and NO2, while a negative effect on its sensitivity for NH3 sensing is observed. Furthermore, our measurements towards H2S suggest that the concentration of In2O3 nanoparticles can induce an uncommon transition from p-type to n-type semiconductor nature when rGO–In2O3 nanocompo-sites operate at temperatures close to 160 °C.

Resume : Light-emitting diodes (LEDs) used as solid-state white light sources are a ground-breaking innovation for the lighting and display markets thanks to the energy consumption savings they allow. Major part of current LED devices converts a blue or near-UV chip excitation into white or coloured light with phosphors containing rare-earth (RE) elements associated to environmental, economic and geopolitical issues. This context has led to the search for alternative RE-free LED phosphor materials. Based on previous works carried out at Néel Institute[1], the development of aluminium borate (AB) phosphors prepared with abundant, low cost and non-toxic precursors will be described here. The AB micronic powders are originally prepared by the modified Pechini method to get a very homogeneous aluminium borate matrix. These innovative luminescent compounds generate a wide and adjustable photoluminescence emission band on the entire visible spectrum under commercial UV LED excitation (365 nm; 385 nm; 405 nm) arising from organic emitting centres (Polycyclic Aromatic Hydrocarbons molecules, PAHs)[2]. The synthesis protocol has been optimized: especially, the reflux step was replaced by microwave-assisted heating. In addition to the time saving of two days on the whole synthetic process, the optical performances of the resulting powders are clearly improved. The PL emission is broadened (colour rendering index > 80), more intense on the whole visible range and tuneable with the excitation wavelength from cold to neutral-warm white. The powders present internal photoluminescence quantum yield (PLQY) up to 45%. The AB powders were then dispersed in a polymer matrix to form homogeneous luminescent coatings. Furthermore, the efficiency and stability of the powders and composite coatings under thermal and photonic stresses will be presented and discussed.

Resume : Thanks to their two-dimensional electron gas (2DEG) obtained from AlGaN/GaN heterojunction, GaN based high electron mobility transistors (HEMT) are interesting for the field of power electronics. For safety uses, HEMTs called “normally-off” with a positive threshold voltage are requested [1]. For that matter, the MOS-channel HEMT (MOSc-HEMT) with its fully recessed AlGaN layer and MOS structure at the gate region is an attractive solution. However, the device performance strongly depends on the dielectric/etched GaN interface [2]. Post-Deposition Anneal (PDA) of the dielectric is one way to improve this interface and the device performance [3], [4]. Furthermore, it is crucial to know the maximum PDA temperature without detrimental impact on the already deposited dielectric in order to optimize the thermal budget for MOSc-HEMT processing. In the scope of reducing the flat-band voltage hysteresis (ΔVFB) without inducing the dielectric crystallization, we investigate the electrical effect of different PDA temperatures for Al2O3 deposited by Atomic Layer Deposition (ALD) on as-grown and etched GaN substrates, through planar capacitive structures. After 500°C, we notice a reduction of both the flat-band voltage (VFB) and its hysteresis (ΔVFB). The hysteresis reduction is correlated to the reduction of OH groups observed using both laboratory Hard X-Ray Photoelectron Spectroscopy (HAXPES) and FTIR analysis. Finally, GIXRD analysis shows a small crystallized orthorhombic κ-Al2O3 signal for a 600°C PDA on etched GaN substrates, which is absent for the same temperature for as-grown GaN substrates. Regarding the subsequent thermal budget of MOSc-HEMT, the implementation of PDA temperature above 500°C can be detrimental for the device with possible subsequent crystallization. References [1] J. He et al., Advanced electronic materials, p. 24, 2021. [2] L. Vauche et al., ACS Appl. Electron. Mater., vol. 3, no 3, p. 1170‑1177, 2021 [3] T. Kubo et al., Semicond. Sci. Technol., vol. 32, no 6, p. 065012, 2017 [4] Q. Zhou et al., IEEE ELECTRON DEVICE LETTERS, vol. 37, no 2, p. 4, 2016.

Resume : Considering how the electrical transistor revolutionized the field of electronics, the realization of an optical transistor should open the long-awaited era of optical computing with superior data processing possibilities. However, such function requires unnatural interactions between photons, absent in most environments. In this talk we will show that a ferroelectric-photovoltaic crystal can act as optical transistor at ambient when gated with the light of its bandgap energy. The photovoltaic charge generation then impacts the internal electric field resulting in a coherent-less optical computing possibility. Thanks to ferroelecticity, our approach is also able to demonstrate an all-optical and even re-writable memory effect. The possibility of integration of these effects with 2D structures will be also discussed.

Resume : Ferroelectric (FE) materials can exhibit a very wide range of properties of interest for many modern applications1. Their switchable anomalous photovoltaic effect as well as their diode-like polarisation dependant conductivity and multiferroicity are particularly interesting for several applications and in particular for light harvesting as active layer2. The characterisation of the electronic and photoinduced effects at nanometric scale in FE-based heterostructures is of relevance for a better understanding and control of the electronic transport, including for the anomalous and the bulk photovoltaic effect whose precise working mechanisms are still under debate. By using atomic force microscopy (AFM) techniques such as piezoelectric force microscopy (PFM), conductive atomic force microscopy (CAFM) or kelvin probe force microscopy (KPFM), coupled with an incident laser, we show that it is possible to study various local photoinduced properties of FE Bi2FeCrO6 (BFCO) thin films. In particular, a polarisation dependant diode-like conduction and a high electronic activity at grains boundaries varying with the polarisation direction are evidenced. These local electronic properties were found dependent on the incident laser intensity. Moreover, because of the mismatch between BFCO and the substrates, the films are strained which has impact on the local properties of BFCO3. The photovoltaic mechanism, conductivity, photoconductivity as well as the charge carrier dynamics and interfacial effects will be also addressed. 1. L. Yin, W. Mi, Progress in BiFeO3-based heterostructures: materials, properties and applications, Nanoscale 12, 477–523 (2020). 2. Y. Yuan, Z. Xiao, B. Yang, J. Huang, Arising applications of ferroelectric materials in photovoltaic devices, J. Mater. Chem. A 2, 6027–6041 (2014). 3. M. V. Rastei, et al. Thickness Dependence and Strain Effects in Ferroelectric Bi2FeCrO6 Thin Films. ACS Appl. Energy Mater. 2, 8550–8559 (2019).

Resume : Recent advances in nano-electronics have seen another breakthrough with IBM unveiling its first 2 nm chip technology. Future progress in nano-fabrication will shortly go beyond this limit, thus raising high the bar for nanoscale electrical characterization and measurements. The currently implemented 5G and its foreseen successor 6G networks are aggressively demanding for very high frequency switching components. While dielectric layers constitute a keystone-element in transistors’ technologies, their electrical properties at the nanoscale (i.e. dielectric constant, loss tangent angle) are of paramount importance to guarantee highly performing technological devices. More specifically, high-k piezoelectric materials steer greater attention owing to their versatility not only in transistor’s technology but as nano-generators, nano-actuators and sensors. Here we present a comprehensive metrological body of work done for the quantification of the dielectric permittivity of two commonly used high-k materials, namely lead zirconate titanate (PZT) and lead – magnesium niobate lead titanate (PMN-PT). Scanning microwave microscopy (SMM), fitted with a vector network analyzer (VNA – 6 GHz) is used to measure micro-capacitive structures prepared by the deposition of gold on polycrystalline rough dielectrics’ surfaces. The capacitance measurements (in the range 0.1 fF to 10 fF) have been carried out applying apply a modified short open-load (SOL) method to calibrate the SMM.. All experimental factors dictating the quantification of high-k dielectric constants (from 400 to 800) with low relative uncertainty levels (less than 10%) are discussed . Interfacial roughness, polycrystalline surfaces, dimensional measurements and parasitic capacitances constitute the main contributors to the overall uncertainty budget. Finite elements modelling of the micro-capacitance structures as well as the frequency dependence of the measured dielectric constants will be presented and discussed.

Resume : α-quartz is an important material for microelectronic industry since it is selected to fabricate the oscillators and transducers present in any electronic device. However, to-date α-quartz applied to microelectronics is exclusively synthetized by hydrothermal methods, which produce big crystals making impossible to decrease their size and for most applications these crystals need to be bonded on Si substrates. This feature represents an important barrier for the microelectronics industry since thinner monocrystalline quartz plates are currently highly demanded for faster device operation, higher frequency filtering or to produce transducers with lower detection levels and improved sensitivity. In the present work, we report the fabrication of the first epitaxial piezoelectric nanostructured (100)α-quartz/(100) Si-based cantilever due to the combination of chemical solution depostion, soft-nanoimprint lithography and top-down microfabrication processes. By using SOI technology, we are able to modify the dimensions and designs of quartz-based cantilevers while preserving a coherent (100)quartz/(100)silicon crystalline interface and piezoelectric properties [1,2]. We have engineered piezoelectric cantilevers exhibited a dimension of 40 µm large and 100 µm long with with a 600 nm thick patterned quartz layer epitaxially grown on a 2 µm thick Si device layer. We measured a resonance frequency at 267 kHz (comparable to similar commercial tip less cantilevers) and the estimated quality factor Q of the whole mechanical structure is Q = 398 under low vacuum conditions. Importantly, we obtained a sensitivity of 1 µN.Hz-1 which results in a mass detection sensitivity of 100 ng Hz-1, using an atomic force microscope. Because quartz-based devices are highly used for chemical and biosensing applications, such as quartz crystal-microbalance-based setups, we determined the biocompatibility of nanostructured α-quartz devices engineered by chemical solution deposition. We confirmed that human epithelial cells, such as HT1080 cells, adhere and can be cultured on patterned epitaxial α-quartz thin films. Moreover, we found that nanostructured α-quartz thin films can induce the self-organization of the epidermal growth factor receptor (EGFR) on cellular membrane. As a result, nanostructured biocompatible piezoelectric quartz-based MEMS could be applied for biosensing applications in the near future. [1] Claire Jolly et al. Soft chemistry assisted On-chip Integration of Nanostructured quartz-based Piezoelectric Microelectromechanical System. Adv. Mater. Technol. 2021, 6, 2000831. [2] Claire Jolly et al. Epitaxial Nanostructured α-Quartz Films on Silicon: From the Material to New Devices. J. Vis. Exp;(164), e61766, doi:10.3791/61766 (2020).

Resume : The large piezoelectric response in Pb-free ferroelectrics gains significant research interest in both fundamental and technological aspects. Generally, the large piezoelectric response is found to be in a material having morphotropic phase boundary (MPB), where material exhibits multiphase coexistence. However, such a giant piezoelectric response in a ferroelectric system is found in a very narrow temperature range correlated with the materials MPB stabilization window. Very recently, there has been a realization of a gamut of materials showing anomalous and giant electromechanical response mediated by defects and their elastic dipoles and fields. These materials (such a Gd doped CeO2, hybrid perovskites etc.) are attracting a lot of interest as a simpler alternative to Pb-based piezoelectric for selective applications. In this work, we have found a giant piezoelectric coefficient (d31) of ~4000 pm/V at 5 kHz and room temperature in a non-stoichiometric epitaxial BaTiO3 (BTO) thin film grown on Si(100). This is a record value observed in any system at such frequencies. The large signal piezoelectric response of the BTO thin film is carried out both along the in-plane and out-of-plane electrode geometries. The out-of-plane piezoelectric coefficient (d33) is found to be ~4 pm/V at 5 kHz, which is quite comparable with the reported result. The physical origin of the extraordinary d31 value is attributed to the large Ti-displacement along the < 110> direction due to Ba-deficiency in the BTO film, which reconfigures the local symmetry and ferroelastic response in surrounding regions. Additionally, the TEM studies illustrate that the structural symmetry of defective BTO film is less symmetry than its conventional tetragonal structure. This work reveals that the formation of local heterogeneity mediated by the defects could be an alternative approach to designing suitable functional materials for piezoelectric MEMS applications in the future.

Resume : Barium titanate (BaTiO3) has been in the spotlight as a dielectric material for electronic devices due to its high permittivity. However, the permittivity and dielectric loss of BaTiO3 are greatly affected by various factors such as tetragonality, grain size or impurities as well as the density of the material. As these factors are altered by synthetic process, it is necessary to optimize the process to synthesize BaTiO3 with high permittivity and low dielectric loss. Among various synthesis methods, solid-state reaction is attracting attention because low-cost mass production is available with advanced technology for atomization and dispersion of BaCO3 and TiO2 precursors. However, it is difficult to optimize the synthetic process for desired permittivity and dielectric loss through trial-and-error experimental approach due to huge numbers of their combinations of various synthetic conditions and the types of precursors that can affect their properties. Herein, we propose a machine learning (ML) approach to efficiently search synthetic process for targeted properties of BaTiO3. We first performed 371 experiments to synthesize BaTiO3 through solid-state reaction with various precursors of BaCO3 and TiO2 with different purity, particle size and specific surface area and various synthetic variables for wet mixing, calcination, and sintering and measured their density, permittivity, and dielectric loss. The correlation analysis is conducted to understand the correlation between the precursors? properties and synthetic variables and BaTiO3?s density, permittivity, and dielectric loss. We found that the density is highly correlated with the sintering holding temperature, the permittivity with the TiO2 particle size, and the dielectric loss with the total concentration of impurities in BaCO3. Then, we developed ML models (Random Forest, Gradient Boost, XG boost) to predict the density, permittivity, and dielectric loss of BaTiO3 according to synthetic conditions including the type of precursor and synthetic variables for each process. Our ML models can predict properties from synthetic conditions with high accuracy. We performed additional experiments with ML-guided synthetic conditions to demonstrate that our ML models allow us inversely design the synthetic process for targeted permittivity and dielectric loss.

Resume : The interest of 2D materials has grown considerable during last years and new additions are continualy included to this family of compounds [1]. One of them are transition metal trichalcogenides (TMTs) [2] materials, which exhibit wide range of bandgaps and intrinsic magnetism, presenting an unique opportunity to integrate optical functionalities with magnetism. The recent theoretical reports have demonstrated that MnPS3 can be inferred indirectly using different polarization of light and exhibits a giant excitonic binding energy [3], pointing the possibility of usage in room temperature optoelectronic devices. Here, we present a comprehensive an ab initio study in the framework of Density Functional Theory (DFT) of the optical properties of TMTs compounds (MPX3, M= Mn, Ni, Co, Fe, X= S, Se) monolayers. These materials are 2D magnets, exhibiting antiferromagnetic ordering of the spins. Hence, the DFT+U approach and spin-orbital interaction (SOI) are included. We demonstrate that the impact of the SOI is significant for these systems and cannot be neglected. Moreover, the valley Zeeman splitting (vZs) is observed for the Mn containing compounds, resulting in non-equivalency of at K+ and K- high symmetry k-points. We also highlight the impact of the Hubbard U correction and the magnetic ordering of the spins on the valley Zeeman splitting. In particular, the largest value of vZs is obtained for MnPSe3 U=3 and equals to 35meV . Furthermore, in the case of the FePX3 compounds, the band splitting is evident. In addition, the impact of the Hubbard U and the magnetic ordering on the curvature of the bands and the dielectric constans are examined. Finally, the large binding energies of band-edge excitons are predicted for all employed systems using the formalism of the Bethe-Salpeter equation combined with the DFT results. We also determine the optical selection rules that show that for materials with a direct gap, they have non-zero oscillator strength of the band edge transition. The study was accomplished thanks to the funds allotted by the National Science Centre, Poland within the framework of the research project ‘SONATA12’ no. UMO2016/23/D/ST3/03446. Access to computing facilities of TU Dresden ZIH for the project ”TransPheMat”, PL-Grid Polish Infrastructure for Supporting Computational Science in the European Research Space, and of the Interdisciplinary Center of Modeling (ICM), University of Warsaw are gratefully acknowledged. [1] Jiang, X., et al. Applied Physics Reviews, 8(3), 031305 (2021). [2] B. L. Chittari et al. Phys. Rev. B 94, 184428 (2016). [3] M. Birowska, P.E.F. Junior, J. Fabian, J, Kuntsmann, Phys. Rev. B 103, L121108 (2021)

Resume : Although the range of applications of Barium titanate (BaTiO3) is gradually widening, the effects of various factors on properties of the dielectric materials has not been fully explored yet. It belongs to the fact of that there are numerous combinations of factors such as characteristics of raw materials and synthetic conditions in each process. Most previous works have relied on well-designed experiments such as regression or ANOVA to identify effect of a factor. Hence, it is still uncovered how to achieve target properties of BaTiO3 by assessing the complicated and compound effects adequately. However, those methods are not tailored for investigating sequential relationships with several factors (i.e. X1?Y?Z). To fill in research gaps, this study aims at investigating the effects of characteristics of raw materials and synthetic conditions on the properties by adopting a structural equation model. A structural equation model is a statistical method used to measure and analyze causal relationships among constructs. Researchers can conduct path analysis, factor analysis, and regression analysis simultaneously in a pre-defined model. To the best of our knowledge, it has not been applied in the field of material science while it is widely adopted in numerous social science studies due to its sophisticated ability of explaining causal relations among factors. Based on 371 observations with 20 variables from real experiments, we conducted a structural equation model analysis. The proposed model is composed of 12 constructs with 20 indicators. Each construct consists of indicators, which reflect both characteristics of raw materials (i.e. density, impurity, specific surface area, particle size of TiO2 and BaCO3) and synthetic conditions in calcination/sintering processes (calcination holding time and temperature, sintering temperature) as well as properties of BaTiO3 (specific surface area, purity, tetragonality, moral ratio) and final properties of BaTiO3(density, dielectric loss, permittivity). Some of them are not continuous variable but desecrate because pre-designed experiments are performed. For example, sintering temperatures ranges from 1,000 °C to 1300 °C. R2 of the proposed model is 72.6%. We found out that the target dielectric loss and permittivity of BaTiO3 is associated with density of BaTiO3 and properties of BaTiO3, which are affected by impurities of BaCO3, calcination time, and calcination temperature. In addition, we also found out that characteristics of TiO2 do not statistically influence on properties of BaTiO3. Several findings and implications are discussed.

Resume : GaN layers were grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on GaAs (110) substrate at temperature varying in the range of 750–900 ◦C. 50 nm-thick GaN layer grown at low temperature (550 ◦C) was used as buffer layer. Scanning electron microscopy (SEM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD) and room temperature cathodoluminescence (RT-CL) studies were carried out and showed a large dependence of the crystalline and optical properties of GaN layer with the growth temperature. A mixture of cubic and hexagonal GaN phases is evidenced by the 2θ/ω spectra which are dominated by a broad peak associated to c-GaN (220) and h-GaN (11.0) reflections. The cubic GaN phase is maximal for a growth temperature of 850 ◦C. At this temperature, morphological observations by AFM showed the presence of c-GaN islands and RT-CL spectra showed only c-GaN (3.23 eV) emission whereas both emissions of c-GaN (3.23 eV) and h-GaN (3.39 eV) were observed at 900 ◦C.

Resume : Zinc orthotitanate, Zn2TiO4, has been paid increasing attention due its wide application in microwave dielectrics, catalysts, pigments, gas sensors, etc. The doping of Zn2TiO4 with Mn produces coloration, improves quality factor and causes photoluminescence (PL) in the red spectral range. However, the control of Mn charge state remains one of the major challenges of Mn doped compounds. In this contribution, the incorporation of Mn in the crystal lattice of Zn2TiO4 has been investigated by X-ray diffraction (XRD), PL and electron paramagnetic resonance (EPR) methods. The samples were produced via sintering in air at 800-1200°C of nanosized ZnO and TiO2 powders. The Mn doped Zn2TiO4 demonstrated PL band peaked at 680 nm due to 2Eg?4A2g transition of Mn4+ ions on Ti4+ cites of Zn2TiO4 crystal lattice. The intensity of red PL increased with the increase of Mn concentration up to 0.1% and showed decay time of about 160 ?s. The decrease of PL intensity was observed in the samples with Mn content larger than 0.1% as well as in the samples sintered at 1200°C. In the last case, the PL decay time did not shorten in contrast to the PL concentration quenching. The PL intensity decrease was accompanied by the appearance of Mn2+ signal in the EPR spectra. It was ascribed to Mn2+ ions on Mg2+ cites of cubic Zn2TiO4. It is concluded that at low Mn concentration (?0.1%) and low sintering temperatures (?1100°C) manganese tends to incorporate in Zn2TiO4 crystal lattice as Mn4+ ions. Both high annealing temperature (>1100°C) and high Mn concentration (>0.1%) hinder formation of Mn4+ centers and promote incorporation of manganese as Mn2+ ion. In the samples sintered at 1200°C, the decrease of concentration of Mn4+ centers is supposed to be one of the reasons of decreased intensity of Mn4+ red PL.

Resume : Layered two-dimensional (2D) materials, such as p-type WSe2, are potential key materials in manufacturing of the next generation electronic devices. One of the remaining main challenges is the large area growth of high-quality 2D films. A potential large-scale 2D WSe2 synthesis method is conversion (selenization) of a pre-deposited sacrificial precursor coating, however, its use is still limited mainly due to lack of understanding of the growth mechanisms involved. Here, we have studied and compared properties of thin crystalline WSe2 films, prepared via selenization of sputter-deposited sacrificial WO3 and W films. Surface morphology of the as-grown films was studied using scanning electron microscope complemented with atomic force microscope. Structural and chemical composition was confirmed by X-ray diffraction and micro-Raman spectroscopy, respectively. On-chip photoconductive devices were made using standard photolithography process and their photoresponse was investigated for 405 nm wavelength light. The obtained results give insight into the growth of crystalline WSe2 via sacrificial film selenization. Financial support of Latvian Council of Science FLPP project lzp-2020/1-0261 is greatly acknowledged.

Resume : During the last decade, hybrid nanocomposites composed by inorganic nanoparticles (np) in an organic polymer matrix have increased scientific interest due to its cost effectivity, industrial scalability and versatility. These materials can take advantage of both the inorganic filler and the organic compound, making them tunable and suitable candidates for a wide variety of applications such as smart coatings, optoelectronics, batteries, sensors, etc. It is a field in continuous expansion, thus the development of new synthesis methods of ultra-thin layers or self-assembled structures compatible with the current technology are necessary. However, guarantee a good control of the nanoparticle concentration and dispersion to a large scale is still a challenge. In this work, we are assessing the potential of Polyvinyl Formal (PVF)-based nanocomposites to deposit homogeneously dispersed or self-assembled np on flat surfaces. The films were pre-deposited by dip coating and transferred onto a target substrate. This simple preparation method would allow for a fast transferring of ultra-thin and freestanding nanocomposite films (few tens of nm thick) onto, hypothetically, any type of substrate with an extraordinary reproducibility in a square cm scale area regardless the np nature, and thus the field of applications would depend in a great extent upon the np properties. In this study highly monodisperse FeOx nanoparticles and CdSe quantum dots and nanoplatelets have been tested as filler materials and their optical properties were analyzed. The effect of the np concentration on the particle arrangement has been studied by atomic force microscopy, scanning and transmission electron microscopy and small angle X-ray scattering. At relatively low concentrations the spherical np do not agglomerate but as the concentration increases they tend to arrange in 2D fashion suggesting that the thin films are mainly composed by np monolayers, forming homogeneously dispersed and self-assembled nanoparticle islands, although the formation of multilayers were observed for high np concentration. Therefore, the method can be used to fabricate more complex functional PVF/np composites and facilitates a way to form large scale self-assembled monolayers of nanoparticles in PVF-based devices.

Resume : Cobalt-containing thin films, in particular metallic Co, are garnering significant interest as next-generation interconnects to replace Cu in future nanoelectronic devices. A review of the current atomic layer deposition (ALD) processes for Co thin films reveals that metal organic reducing agents have not been explored as co-reagents.[1] This is surprising considering the ALD history of its “competitor” Cu and the reports on processes employing several Cu(I/II) precursors being reduced with the well-known Zn(Et)2.[2,3] However, deposition of copper using this Zn-containing reductant resulted in unwanted Zn contamination owing to the low thermal stability and CVD-type behavior of Zn(Et)2.[4] This presentation describes the development of a new and promising ALD process yielding Zn-free thin films of Co, employing CoCl2(TMEDA) as Co precursor and an intramolecularly stabilized Zn(II) aminoalkyl, Zn(DMP)2,[5] as Zn precursor. The precursor pair has been chosen based on an initial reactivity study encompassing several Zn precursor candidates. This study also allowed to mechanistically rationalize the surface chemistry that allows formation of metallic Co during the ALD process.[6] For the precursor pair CoCl2(TMEDA) / Zn(DMP)2, a full ALD process study was carried out on 2-inch Si(100) wafers. Typical ALD growth characteristics in terms of saturation were found for both Co and Zn precursor pulses and a strong dependency of the growth per cycle (GPC) on the deposition temperature was observed. The film thickness scaled linearly with the number of deposition cycles, confirming ALD behaviour. Combined AFM and SEM measurements of thin films obtained from the optimized process revealed the smooth and pinhole-free character of the layers and roughness scaled nearly linearly with film thickness. Complementary RBS/NRA and XPS investigations on selected Co thin films confirmed their metallic nature and the absence of Zn. While other impurity levels were low as well, the C contamination amounted to 20 at.%. Nevertheless, resistivity measurements of Co thin films directly grown on insulating SiO2 substrates yielded promising values of 15 - 20 μΩ cm close to bulk resistivity.[6] Contrasting this, ALD depositions employing other Zn-containing reductants yielded thin films that mostly consisted of Zn. This new approach signifies the paramount importance of precursor choice for developing ALD processes that are particularly challenging for metal films. [1] https://www.atomiclimits.com/alddatabase/. [2] Z. Zhong, et al., Thin Solid Films 2015, 589, 673. [3] B. H. Lee, et al., Angewandte Chemie (International ed. in English) 2009, 48, 4536. [4] T. Muneshwar, et al., JVST A: Vacuum, Surfaces, and Films 2016, 34, 50605. [5] L. Mai, et al., Small 2020, 16, e1907506. [6] D. Zanders et al., Chem. Mater 2021, [Editors‘ Choice]

Resume : In recent years much research has focused on the use of hybrid plasmonic nanostructures for the nanoscale control of electromagnetic radiation. By taking advantage of the surface plasmon resonances and highly concentrated electric fields arising from the interaction between visible light and metallic nanoparticles, a diverse range of applications within nanophotonics has been realised. Among these applications, methods to modify the luminescence of quantum emitters is an area of particular interest. The photoluminescence of an emitter in a coupled nanoparticle system is highly dependent on several factors including spectral overlap between the emitter’s absorption and emission with the plasmon resonances of the nanostructure. As the plasmonic resonances are reliant on factors set during the fabrication process, we consider tunable plasmonic structures formed by placing the metallic nanostructures on a thin film of phase change material VO2. As a phase change material VO2 undergoes a large, reversible transition from a monoclinic semiconducting phase to a rutile metallic phase at a critical temperature of 68C, relatively close to room temperature. In addition to a thermal transition, this phase change has been induced electrically and optically at significantly lower thresholds than rival phase change materials. The phase change in underlying thin film VO2 blueshifts the plasmonic response of coupled nanoparticles and therefore allows modification of the interaction between the structure and coupled emitters. By selecting appropriate nanostructures and emitters we have developed a hybrid system that can used for dynamic luminescence enhancement and for compensation of thermally induced luminescence enhancement quenching. This allows for improved emission in devices operating at elevated temperatures. In an optimised system comprising of a Ag nanodisc-VO2 film and Alexa Dye emitter, luminescence enhancements of over a factor of 4 can be seen therefore allowing compensation for thermal quenching of up to 70% between room temperature and 70C. Modification of the VO2 phase change temperature through strain or doping offers further increase in photoluminescence, making the hybrid structures promising candidates for dynamic photoluminescence enhancement.

Resume : This work is devoted to the issues of numerical simulation of field Hall sensors based on "silicon-on-insulator" nanostructure with two control gates. A multiscale mathematical model is developed, according to which the longitudinal distribution of electrons layer concentration in the conducting channel is determined by solving a series of one-dimensional Schrödinger-Poisson equations with varying boundary conditions, after which the element current characteristics are calculated. For the computer realization of the constructed multiscale model the original software is constructed, including the system of information support of calculations and analysis of results. The created computer model makes it possible to calculate different variants promptly, which forms the basis for multivariant parametric analysis. The influence of temperature on the characteristics of the sensor is analyzed. The experimental study of current characteristics was carried out in the range of temperatures 8 - 600 K. The obtained results allow to draw a conclusion about an opportunity of sensor functioning in a wide range of temperatures. A parametric identification of the developed multiscale model by experimental data was carried out. An approximation dependence of the charge carriers mobility on the temperature and concentration is proposed. The calculation results are in agreement with experimental data in a wide range of temperatures, supply voltages and gate voltages. The sensitivity function of the electric current to temperature change is obtained, which allows us to estimate the required sensitivity of the sensor for determining the temperature with a given accuracy. Optimization of sensor characteristics (reduction of power consumption, increase of sensitivity) using the developed means of multiscale modeling creates conditions for development of unique nanoscale sensitive elements, sensors of magnetic and temperature fields by changing the structural characteristics of the heterostructure.