Solid State Phenomena Vol. 312

Abstract: The structure, phase composition, and morphology of FeSi and FeSi₂ nanofilms grown by three alternations of Fe (with a wedge-shaped thickness in the range 0 ‒ 2 ml) and Si (with a thickness 1 ML) depositions on a Si (001) 2×1 substrate heated to 400 °C were studied. According to Auger electron spectroscopy and electron energy loss, FeSi and FeSi₂ films were formed before and after the third deposition of Si, respectively. With this, a FeSi₂ film had ~1.5 ML of Si, which segregated on its surface. Both films consisted of a wetting coating (WL) and bulk phase forming at 2‒3 ML and after 3 ML of Fe, respectively. According to data of low electron energy diffraction, these films had a nanocrystalline structure. Moreover, according atomic force microscopy, deep square pores were formed in FeSi₂ films. They had a depth of 18‒10 nm, which was decreased and then increased before and, respectively, after Fe thickness ~ 3 ML.

Abstract: The atomic structure and morphology of cerium oxide nanoparticles obtained by laser ablation are experimentally and theoretically investigated. Using transmission electron microscopy, X-ray diffractometry, and electron energy loss spectroscopy, it has been shown that particles are enriched in oxygen vacancies that stabilize their internal structure. The density functional method was used to study the dependence of the unit cell parameter of CeO₂ nanoparticles on their size. An analysis of the charge density distribution shows a different structural distribution of Ce³⁺ and Ce⁴⁺ atoms in nanoparticles.

Abstract: The paper presents the results of experimental studies of a photoactive catalyst in the form of barium titanate fibers with deposited particles of nickel, platinum and gold. Barium titanate fibers were synthesized by the molten salt method. The obtained barium titanate fibers were studied by SEM, TEM, XRD, and Raman spectroscopy. Photocatalytic studies showed that barium titanate fibers with platinum nanoparticles are the most active of the three prepared Metal/BaTiO3 samples.

Abstract: In this work, germanium nanowires (GeNWs) were fabricated by galvanostatic electrodeposition using In nanoparticles from water solutions at different temperatures. It was found that in the temperature range from 10°C to 60°C there was no significant change in the structure of GeNWs, and the average diameter was about 40 nm. The growth time of GeNWs increases linearly with increasing temperature of the electrolyte solution. However, the structure of GeNW obtained at a solution temperature of 90°C has changed. It was shown that these GeNWs have a core-shell structure: the core is a crystalline Ge phase containing In atoms, and the shell is Ge oxides (hydroxides).

Abstract: Electrical conductance of Si(111)6×6-Tl and Si(111)β√3×√3-Bi surfaces has been monitored in the course of fullerenes deposition. It has been found that dependence of surface conductivity on the adsorbed C60 dose can be understood in terms of charge transfer induced by interaction of fullerene molecules and substrate which can be explained by the acceptor-like behavior of fullerenes. For the Si(111)6×6-Tl surface decreasing of conductance is connected with depletion of metallic bands of the Tl double layer. For the Si(111)β√3×√3-Bi surface the conductivity is almost unchanged with C60 dose, but due to the fact that C60 layer on this surface form close-packed hexagonal arrays in the layer-by-layer mode, it can be used as a template for alkali-induced ultra-thin fulleride formation.

Abstract: We report on the results of a study of the lateral photovoltaic effect in the Fe₃O₄/SiO₂/n-Si(001) structure at temperatures of 300 and 122 K under continuous and pulsed illumination. It is found that when the temperature changes from 300 to 122 K, the LPE sensitivity decreases from 112 to 65 mV/mm. At pulsed illumination, an increase of rise time and a fall time is observed with decreasing temperature. From a consideration of the energy band diagrams and equivalent circuits of the Fe₃O₄/SiO₂/n-Si structure, it is assumed that the detected temperature effects of LPE are due to the strong dependence of the magnetite film resistance on temperature.

Abstract: We report on the results of a study of the lateral photovoltaic effect in theFe3O4/SiO2/n-Si structure grown on Si(001) and Si(111) substrates. It was found that in theFe3O4/SiO2/Si(001) structure the LPE sensitivity is a half times as much, and the photoresponseparameters are about 3 times less than those in the Fe3O4/SiO2/Si(111) structure. It is supposed thata higher sensitivity and faster photoresponse in the Fe3O4/SiO2/Si(001) structure, compared with theFe3O4/SiO2/Si(111) structure, are caused by a lower density of surface states at the SiO2/Si(001)interface than at the SiO2/Si(111) interface.

Abstract: Here, we showed formation of chiral nanoprotrusions upon direct laser ablation of bulk crystalline silicon (c-Si) wafer with single femtosecond (fs) pulses having asymmetric donut-shaped intensity profile. Breaking circular symmetry of the irradiating donut-shaped fs-pulse beam was demonstrated to switch the geometry of formed surface nanoprotrusions from regular to chiral, while the chirality of the obtained Si nanostructures was found to promote with a degree of asymmetry of the laser beam. The obtained experimental results explain, for the first time, the formation of previously reported chiral c-Si nanostructures produced via donut-shaped beam ablation in terms of uneven helical flow of laser-melted Si material caused by asymmetry of initial intensity and temperature pattern on laser-irradiated Si surface. Our findings open a pathway towards easy-to-implement inexpensive fabrication of chiral all-dielectric nanostructures for advanced nanophotonic applications.

Abstract: Here, we demonstrate formation of spherical-shaped amorphous titania (TiO₂) nanoparticles decorated with Au nanoclusters via nanosecond pulse ablation (7-ns, 532-nm wavelength) of commercially available TiO₂ nanopowders dispersed in an aqueous solution of chloroauric acid (HAuCl₄). Generation of such hybrid nanostructures was found to be caused by laser-induced remelting of the initial TiO₂ nanoparticles, stimulated by Au nanoclusters that can adsorbed on their surface and boost light-to-heat conversion process in optically transparent titania. The morphology and chemical composition of the obtained hybrid nanomaterials were studied in detail via scanning electron microscopy, Raman spectroscopy and Energy Dispersive X-ray spectroscopy. The average size and number of Au nanoclusters reduced on the TiO₂ nanoparticle surface was shown to be tuned by varying the initial nanoparticles/HAuCl₄ concentration ratio. Spectroscopic measurements of single hybrid nanoparticles scattering, as well as the corresponding numerical calculations of electromagnetic fields structure near their surface indicate synthesized functional nanomaterials as extremely promising for numerous applications of modern optics, optoelectronics and nanophotonics, e.g., realization of advanced chemo-and biosensing platforms, as well as of new-generation solar cells.

Abstract: The photoluminescence intensity in lithium niobate crystals close to the stoichiometric composition is lower than in a congruent crystal was established. An increase in the Li / Nb ratio leads to a shift in the photoluminescence bands to the short-wavelength region of the spectrum and a change in the fundamental absorption edge of the crystals under study. It was shown that, in addition to point defects in the cationic sublattice, complex defects due to the presence of OH groups in the structure can also contribute to photoluminescence.