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We propose, fabricate, and evaluate strain-induced InGaAs/InAlAs superlattice (SL), which can efficiently radiate broadband terahertz (THz) waves. By means of optical pump-probe measurements, we demonstrate ultrashort photocarriers relaxation times of τ ∼ 1.7 ps without Be-doping of InGaAs photoconductive layers. We assume two dominant mechanisms to be responsible for a sharp reduction of τ in strained SL, which are photocarriers scattering at InGaAs/InAlAs heterointerface roughness and the decrease in the energy bandgap of InGaAs photoconductive layers due to the residual strain. The THz time-domain spectroscopic measurements reveal the rise in both emitted THz waveform and spectrum amplitudes with an increase of the residual strain in SL, in particular, at the low-frequency region. We refer this to the band structure engineering due to the residual strain in SL—since InGaAs photoconductive layers become compressively strained, this reduces the semiconductor's energy bandgap, thus more photocarriers can contribute to the THz emission. The results might be of specific interest for the development of portable THz pulsed spectroscopic and imaging systems and other fundamental and applied aspects of the THz science and technology. [ABSTRACT FROM AUTHOR]

The structure and sensing properties of SnO2–In2O3 composites synthesized by the impregnation method are studied. These composites consist of In2O3 nanocrystals comprising SnO2 nanoclusters with a size of 5–7 nm on their surface. Using energy-dispersive X-ray spectroscopy, it is found that the SnO2 nanoclusters contain indium ions, which provide an increase in the number of catalytically active oxygen vacancies in them. The maximum efficiency of the synthesized composites for hydrogen detection in air is achieved at a SnO2 content in the composite of about 40 wt %. In this case, the high sensor sensitivity of the composite is attributed to the catalytic activity of SnO2 clusters containing indium ions and the high specific surface area of SnO2 aggregates, which provide the conductivity of the composite. [ABSTRACT FROM AUTHOR]

In this paper, submicron SiC thin films are obtained on α-Al2O3 (0001) substrates from a ceramic target in vacuum by means of pulsed laser deposition. The influence of the substrate temperature on the composition, structure and surface morphology of the experimental samples is studied using scanning and transmission electron microscopy, scanning probe microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and Raman spectrometry. It is shown that at Tsub = 1000°C the heteroepitaxial growth of 3C-SiC is observed with the following preferential orientation with respect to the substrate: [ ]Al2O3||[111]SiС and [ ]Al2O3||[ ]SiС, [ ]Al2O3||[ ]SiС. The shape of the reflections from the {011} and {131} 3C–SiC planes on the electron diffraction pattern indicates the presence of local regions in the film that are rotated at angles of up to 7.5° around the growth axis. Thus, it is found that the 3C–SiC film obtained on α‑Al2O3 at a substrate temperature of 1000°C has a mosaic structure partially compensating for the mechanical stresses arising from a mismatch between the lattice parameters and thermal-expansion coefficients along the basal plane. [ABSTRACT FROM AUTHOR]

The structural characteristics, valence states, and distribution of cerium ions between the components in In2O3-CeO2 and SnO2-CeO2 nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In2O3 crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO2 clusters with a surface of SnO2 matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In2O3-CeO2 system, where the addition of CeO2 does not affect the conduction activation energy, where cerium oxide is added to SnO2, the observed increase in the resistance of a SnO2-CeO2 composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO2 crystals as, a result of the penetration of cerium ions into these layers. [ABSTRACT FROM AUTHOR]

The fitting of θ/2θ and ω peaks in X-ray diffraction curves is shown to be most accurate in the case of using an inverse fourth-degree polynomial or probability density function with Student’s distribution (Pearson type VII function). These functions describe well both the highest-intensity central part of the experimental peak and its low-intensity broadened base caused by X-ray diffuse scattering. The mean microdeformation ε and mean vertical domain size D are determined by the Williamson-Hall method for layers of GaN (ε ≈ 0.00006, D ≈ 200 nm) and Al0.32Ga0.68N (ε = 0.0032 ± 0.0005, D = 24 ± 7 nm). The D value obtained for the Al0.32Ga0.68N layer is most likely to result from the nominal thickness of this layer, which is 11 nm. [ABSTRACT FROM AUTHOR]

The effect of Co3O4 and ZrO2 additives on the sensory response of In2O3-based nanostructured composites to H2 and CO is studied. It is shown that the addition of small amounts of Co3O4 or ZrO2 to In2O3 leads to a sharp increase in the sensory response to hydrogen. The maximum sensory response of the ZrO2−In2O3 composite to 1100 ppm of hydrogen increases from 80 to 270 as the ZrO2 content changes 0 to 20 wt %. The response to CO varies only slightly. For Co3O4−In2O3 composites, the maximum response to H2 and CO increases with the Co3O4 content within 0−10 wt %. A further increase in the Co3O4 content leads to a significant decrease in the response, with composites containing ∼60 wt % Co3O4 being characterized by a very low efficiency. In the Co3O4−In2O3 system with a content of up to 60 wt % Co3O4, electronic conduction is realized, which changes to hole conduction at Co3O4 within 80−100 wt %. In the ZrO2−In2O3 system, electric current flows through In2O3 nanocrystals, i.e., n-type conduction takes place. Possible reasons for the observed effects are discussed. [ABSTRACT FROM AUTHOR]