Solid State Phenomena Vol. 312

Abstract: The features of the structure of single crystals LiNbO₃:B³⁺ (0.12 and 0.18 wt %) grown by the Czochralski method from the mixture of different genesis were studied. It was found that boron is able to incorporate into the crystal structure of lithium niobate in a trace amounts (~ 10^–4–10^–5 wt %), decreasing the concentration of structural defects Nb_Li. Thus, ordering of structural units of the cation sublattice of lithium niobate crystals grown from a congruent composition melt approach in that of stoichiometric crystals.

Abstract: We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Abstract: It was shown that laser conoscopy can visually detect even slight changes in the optical characteristics of a crystal when it is doped. It has been found that the defective structure of LiNbO₃:Zn (4.5 mol. %), LiNbO₃:Mg (3.0–5.5 mol.%) crystals associated with an uneven entry of an impurity leads to a local change in the elastic characteristics of the crystal and the appearance of mechanical stresses that distort the conoscopic patterns. This can be an abnormal optical biaxiality, which manifests itself in the form of a rupture and enlightenment of the "Maltese cross" in the center of the conoscopic crystal pattern, or local birefringent inclusions that are recorded as additional interference patterns against the background of the main conoscopic pattern, both in the center of the field of view and in its peripheral area.

Abstract: Direct femtosecond laser printing was used to fabricate circular-and coaxial-shaped hole arrays at ultrafast printing rate up to 10⁶ elements per second. To achieve such fast printing rate, we implemented a spatial multiplexing of either a single Gaussian or cylindrical vector beams into linear array of identical laser spots. Being compared to ordinary microholes, the coaxial openings arranged at the same periodicity demonstrate enhanced transmission in the mid-IR spectral range resulted from coupling between localized electromagnetic mode supported by coaxial unit cell and the lattice-type surface plasmon resonance. At optimized geometry of the coaxial openings and their arrangement we demonstrated resonant transmission as high as 92% at wavelengths ranging from 7.5 to 9 μm. This makes the coaxial microhole arrays with tailored spectral properties produced with ultrafast and inexpensive direct laser printing promising for sensing applications based on surface enhanced infrared absorption.

Abstract: Direct laser processing of various materials with nano- and femtosecond (fs) laser pulses is known to be a facile and inexpensive technology for fabrication of various surface morphologies. Since ultrafast deposition of the laser energy to target material typically creates unique experimental conditions with extremely high pressure and temperature, we hypothesized that carrying out this process in anhydrous non-oxidizing environment containing functionalizing agent (fluorophore with vinyl functional group) will allow one-step fabrication and subsequent functionalization of the surface of high-n material. In this paper, we demonstrate successful implementation of this idea by fabricating high-spatial-frequency laser-induced periodic surface structures (LIPSS) via direct fs-pulse ablation of bulk crystalline Si wafer immersed in solution of N-vinylcarbazole in toluene. Laser processing with linearly polarized fs-laser pulses was found to produce LIPSS with a characteristic period around 100 nm functionalized with N-vinylcarbazole molecules via photo-activated hydrosililation reaction. The unique LIPSS with hierarchical roughness and remarkable light trapping performance functionalized with sensory fluorophore show high sensitivity due to implementation of surface enhanced fluorescence effect. By using N-vinylcarbazole as functionalizing agent we demonstrate one-step fabrication of high-performance sensor for detecting nitrobenzene in water with a detection limit of 40 nM.

Abstract: Morphology, structure, magnetic properties and magnetic circular dichroism (MCD) were studied for the Fe_xS_y and Fe_xSe_y nanoparticles (NPs) synthesized with the polyol mediated and the thermal decomposition processes, correspondingly, at different regimes. For all NPs samples, but Fe₃S₄, MCD was measured for the first time. It has been shown that in the case of sulfides, the character of the MCD spectrum changes as the NPs phase composition transforms from Fe₃S₄ to FeS with the synthesis temperature increase. At the same time, the shape of the MCD spectrum is almost independent of the NPs phase in the case of iron selenides

Abstract: On a film of aluminum oxide (Al₂O₃) formed by electrolytic oxidation in distilled water (DW), the growth, transformation of its nanoporous structure, and the generation of electroluminescence (EL) in ketones and related compounds containing carbonyl groups were studied. For those contributing to the brightest EL – acetylacetone and methylpyrrolidone, it was found that the processes described in these electrolytes proceed with the highest intensity. Under the same electrolytes and conditions, similar processes, but with a lower intensity, proceed for A₂O₃ formed on pure aluminum. It was found that, with the external voltage, thermodynamic and geometrical parameters of the electrolytic system being constant, the brightness characteristics of the EL of the anodic Al₂O₃ are influenced by its structural organization and the electrophysical characteristics of the electrolyte surrounding the oxide film, which is proposed to be arbitrarily called “nonelectrolysis” because electrolysis products are not revealed in it.

Abstract: In the present work, bismuth-based nanoparticles of various compositions were obtained by pulsed laser ablation of a metallic bismuth target in water and air using a Q-switch Nd:YAG laser (wavelength of 1064 nm, pulse duration of 7 ns, frequency of 20 Hz, and pulse energy of 160 mJ). Then the samples were annealed in air at temperatures up to 600°C. A comparative analysis of the obtained powders was carried out using methods of X-ray diffraction, transmission electron microscopy, specific surface area measurements, IR-Fourier and UV-Vis Spectroscopy. The photocatalytic activity of the synthesized materials in the process of Rhodamine B decomposition under irradiation of a LED source (375 nm) was also studied.

Abstract: Despite basic optoelectronic properties of metal-organic perovskites are quite robust to defects, thelatter affect performance of related photovoltaic devices made of such promising materials. Recently,direct femtosecond projection lithography appeared as prospective tool for high-performing nondestructivenano- and microstructuring of perovskite films. Here, we study in details how defects affectthe photoluminescence properties of CH3NH3PbI3 hybrid perovskite films patterned with single- andmulti-pulse irradiation with flat-top femtosecond laser pulses. Scanning electron, wide-field multiphoton,photoluminescence and laser confocal microscopies being combined with photoluminescencedecay measurements are carried out for these studies. The obtained experimental results are analyzedwith a model for carriers kinetics allowed to determine contributions from radiative and non-radiative processes.

Abstract: Mixed-halide perovskite allows to realize conception of light-emitting solar cell (LESC) due to possibility to in-situ change device band structure by formation of dipole layer under applied voltage and intrinsic properties of perovskite ions. LESC has optimized perovskite-based solar cell (SC) architecture, but light-emitting diode (LED) regime performances is still low. Defect passivation can improve LED efficiencies due to reducing nonradiative recombination via defect levels. Solvent annealing allows to regulate film formation process and leads to better morphology and grain size for our application. Defect density is significantly reduced due to this passivation method. Here we demonstrate effect of annealing in vapors of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) atmosphere on LESC photovoltaic characteristic, electroluminescence (EL) peak wavelength and photoluminescence quantum yield (PLQY) of mixed-halide perovskite film.