Key Engineering Materials Vol. 806

Abstract: The effect of surface chemical treatment on current-voltage (IV) characteristics of high-resistance MBE-grown PbSnTe:In films in space charge limited current (SCLC) regimes has been studied. At T=4.2 K depending on surface chemical treatment the current in films in SCLC regimes under no illumination could rise up to 10⁴ times and even more. The surface chemical treatment also affected both the value and behavior of the photocurrent. The qualitative model for the observed phenomena has been discussed.

Abstract: The electronic structure of nickel iodide monolayer in NiI₂/ScX₂ (X = S, Se and Te) and NiI₂/NiTe₂ heterostructures was investigated by density functional theory (DFT). The spin-asymmetric semiconducting behavior of NiI₂ monolayer in these interfaces was observed. The width of the band gap of the NiI₂ monolayer practically does not change in heterostructures and remains at the level of 1.7 and 3.0 eV for minor and major spin channels, respectively. The NiI₂ layer can be p-doped by stacking with ScX₂ dichalcogenides. On the contrary, charge transfer (~0.01 |e| per f.u.) from NiTe₂ leads to n-doping of NiI₂. As a result, the Fermi level shifts up to the area of NiI₂ conduction band with spin down carriers only, which gives prospects of using this material in spin filter applications. The electronic structure of NiI₂/ScTe₂ under isotropic deformation in the plane remains the same under tension and compression within 5%, except for a small change in the band gap in the composite layers of NiI₂ within 25%. This allows one to conclude about the stability of the electronic properties under deformations, which gives possibility to use the heterostructures in flexible electronics devices.

Abstract: In this paper, natural heterogeneities of the potential on the degenerated semiconductor surface are discussed as well as the barrier height fluctuations in metal-semiconductor contacts. In the case of electroactive dopant linear screening, characteristic values of chaotic potential amplitudes have been defined. The dependence is shown of these heterogeneities on semiconductor electrophysical parameters.

Abstract: This paper examines the influence of etching regimes on the reflectance of black silicon formed by Ni-assisted chemical etching. Black silicon exhibits properties of high light absorptance. The measured minimum values of the reflectance (R-min) of black silicon with thickness of 580 nm formed by metal-assisted chemical etching (MACE) for 60 minutes at 460 lx illumination were 2,3% in the UV region (200–400 nm), 0,5% in the visible region (400–750 nm) and 0,3% in the IR region (750–1300 nm). The findings showed that the reflectance of black silicon depends on its thickness, illumination and treatment duration. In addition, the porosity and refractive index were calculated.

Abstract: The morphology and structure of iron silicide nanorods formed on Si (111) vicinal surface by the SPE method at T = 630 °C were studied. Optimal Fe coverage and Fe deposition rate for the formation of a dense array of the nanorods (54-65% of the substrate area) on Si (111) surface with 3-4^o miscut angles were established. The aspect ratio of the nanorods is 1.9 – 3.3. Cross-sectional images of a high-resolution transmission electron microscopy (HRTEM) have shown that the nanorods have α-FeSi₂ crystal structure. They are strained along the “a” axis and stretched along the “c” axis, which increased the unit cell volume by 10.3%. According to HRTEM image analysis, the nanorods have the following epitaxial relationships: α-FeSi₂[01]//Si [10] and α-FeSi₂(112)//Si (111). All the data obtained have provided, for the first time, a direct evidence of α-FeSi₂ nanorods formation on Si (111) vicinal surface without noticeable penetration of Fe atoms into the Si substrate.

Abstract: In this paper, the ordering of the arrays of TiO₂ nanotubes obtained by the method of anodic oxidation in the fluoro-containing aqueous-nonaqueous electrolytes containing glycerine and surface-active materials is investigated. For analysis of ordering, the two-dimensional Fourier spectrum, do-it-yourself configurational geometrical entropy and section of the two-dimensional autocorrelation function were used. These characteristics allow us to identify a nature of ordering in sufficient detail and to obtain the preliminary quantitative assessments of this order. It is found that, in the systems of titanium-oxide nanotubes, the stable, almost correct short-range order is established within the first coordination sphere. Such order is similar to the amorphous ordering. At the same time, the ordering of nanotubes arrays differs in detail from the amorphous one in the greater expressiveness of the typical scale the sizes of which can be estimated using the Fourier spectra as well as autocorrelation function.

Abstract: The process of crack propagation from the initial pore in the microstructures of WC-Co alloys with different volume fraction of the cobalt phase was studied by simulation of the stressed state by the finite element method. A calculation of the energy release rate during the propagation of crack through sections which consist of the carbide grains and the cobalt phase was made. It is shown that the strain energy release rate increases with crack propagation in WC grains and decreases with crack propagation in the intermediate layers of cobalt. The maximum stresses required for the destruction of the cobalt layer determine the strength of the entire microstructure. The strength of the alloy increases when decreasing pore diameter and increasing the cobalt phase fraction.

Abstract: The oxide layers on titanium were formed by plasma electrolytic oxidation technique in acid aqueous electrolytes containing sodium tungstate and copper acetate. The coatings with WO₃-CuO or WO₃-CuWO₄ oxide layers have been formed in the electrolytes with H₂C₂O₄ (pH~6) or H₂SO₄ (pH~4) accordingly. The coatings with WO₃-CuWO₄ have a developed surface architecture. The surface is constructed from coral-like structures with lamellar nanocrystals containing copper tungstate and tungsten oxide. The layers of tungsten oxide nanocrystals occupy the depressions between these structures. The band gap of the mixed WO₃CuWO₄ oxide layers is 2.8 eV.

Abstract: Interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane in xylene and under mechanochemical activation conditions has been investigated. The interaction of the above reagents under mechanical activation conditions proceeds with formation of soluble polymers similar to those obtained in a solution with the silicon/molybdenum ratio equal to 2.6. The crystal chemistry parameters of the fraction obtained in solution with the ratio Si/Mo = 1:2 have been calculated on the basis of the X-ray diffraction analysis data using the Debye–Shearer equation. It has been demonstrated that the chain cross-section found using the Miller–Boyer method coincides with that calculated geometrically on the basis of literature data on bond lengths and angles.