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The artificial olfaction units (or e-noses) capable of room-temperature operation are highly demanded to meet the requests of society in numerous vital applications and developing Internet-of-Things. Derivatized 2D crystals are considered as sensing elements of choice in this regard, unlocking the potential of the advanced e-nose technologies limited by the current semiconductor technologies. Herein, we consider fabrication and gas-sensing properties of On-chip multisensor arrays based on a hole-matrixed carbonylated (C-ny) graphene film with a gradually changed thickness and concentration of ketone groups of up to 12.5 at.%. The enhanced chemiresistive response of C-ny graphene toward methanol and ethanol, of hundred ppm concentration when mixing with air to match permissible exposure OSHA limits, at room-temperature operation is signified. Following thorough characterization via core-level techniques and density functional theory, the predominant role of the C-ny graphene-perforated structure and abundance of ketone groups in advancing the chemiresistive effect is established. Advancing practice applications, selective discrimination of the studied alcohols is approached by linear discriminant analysis employing a multisensor array’s vector signal, and the fabricated chip’s long-term performance is shown.

Data on thermally stimulated depolarization current (TSDC) study of the same poled glass in the temperature range 100–1000 K are analyzed. Four specific temperature ranges in the TSDC spectrum of this glass are identified, with each range being attributed to the charge relaxation processes of different natures. During linear heating in the temperature range 100–250 K, charge relaxation is related to the adsorption/desorption of particles from the atmosphere, supposedly water cluster ions H+(H2O)n. The next TSDC band, which is observed at room temperature and above, is related to the disordering of the polar structural entities. The TSDC band in the temperature range 500–750 K is attributed to the relaxation of spatial charge by the diffusion mechanism. The TSDC band in the temperature range 750–1000 K is attributed to the relaxation of spatial charge by the viscous flow mechanism. All these data allowed drawing a schematic TSDC spectrum of silicate glasses in the full temperature range.

We present a study of the process of reduction of thin graphene oxide (GO) films consisting of flakes with lateral size of up to 100 μm through soft ultraviolet irradiation in the argon atmosphere. It was found out that the reduction process leads to a significant decrease in the overall content of the basal-plane functional groups, namely, epoxides and hydroxyls, but with simultaneous increase in the total number of the edge-located carboxyl groups. Obtained transmission electron microscopy images showed that this effect is related to formation of nanoscale holes in the course of reduction. Based on the data obtained, we have proposed a mechanism of the observed GO structural modification in terms of photoinduced chemical reactions between the carbon network and functional groups. These reactions result in progressive growth of the initially existing and newly formed vacancies with formation of the nanoholes with size of up to 100 nm. Thus, reduced graphene oxide films with the restored conjugated network and many edges terminated with carboxyl groups can be probably obtained via the photoreduction process in the argon atmosphere and further used in several applications, such as production of gas sensors and organic light-emitting devices.

It has been experimentally shown that water vapor thermal treatment of silicate glasses with silver ions introduced by ion exchange leads to the formation of a silver nanoparticle layer with a high packing density on the glass surface. The results of studying the morphology of samples by atomic force and electron microscopy and X-ray spectral analysis of the composition of nanoparticles, as well as the optical density and luminescence spectra in different stages of the treatment, are presented. Mechanisms explaining the processes responsible for silver nanoparticle formation upon water vapor thermal treatment on the glass surface after ion exchange are proposed.

The optical and electrical properties of light-emitting diode structures with an active layer based on nanocomposite polyvinylcarbazole (PVK) films doped with nanoparticles of another light-emitting polymer, MEH-PPV, have been studied. It has been established that the size of MEH-PPV particles in the PVK matrix is of the order of 100 nm. The spectral range of photoluminescence of such structures can be changed by varying the ratio of PVK to MEH-PPV. The current-voltage characteristics of composite light-emitting diodes based on PVK: MEH-PPV films indicate p-type conductivity. It has been shown that a decrease in the MEH-PPV nanoparticle concentration in the PVK matrix shifts the threshold values of the bias for the onset of electroluminescence toward smaller values and makes the photoluminescence and electroluminescence spectra more similar to the spectrum of the white light-emitting diode. The influence of the form of the polymer and polymer nanoparticles on the mechanisms of injection and transport of charge carriers and the radiative recombination in the studied structures has been discussed.

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.

This paper presents the experimental results of synthesizing silver nanoparticles in the near-surface layers of glasses by heat treatment in water vapor. It is shown that the presence of a cracked layer on the glass surface has a substantial effect on the shape of the silver nanoparticles, and this manifests itself in the absorption spectra of the glasses. It is established that, when silver is introduced by thermal diffusion from a film, the silver nanoparticles have the shape of oblate ellipsoids in nanocracks and on the glass surface, whereas they acquire a spherical shape in the volume of the glass. It is shown that, when silver is introduced into glass by ion exchange and the glass is later heat-treated in water vapor, part of the silver emerges onto the glass surface, forming a structured film.

Combined approach based on X‐ray reflectometry (XRR), atomic‐force microscopy (AFM), and small‐angle X‐ray scattering (SAXS) has been applied to two series of multilayer Mo/Si mirrors grown by magnetron sputtering on standard and specially smoothed substrates under different technological conditions (Aand B). Simulation of XRR data, using a model of two layers in period, can distinguish the mirror quality in terms of the total root mean square roughness. The quality is better for mirrors grown on smoother substrate, but it also depends on technological conditions. In addition, use of a model with transition layers reveals an asymmetry of Mo/Si and Si/Mo interfaces. Analysis of surface roughness PSD functions obtained by AFM shows that the surface diffusion is the dominant smoothing mechanism for all the mirrors studied. The low‐frequency roughness is conformal to that of the substrate for better mirrors (series A), but increases for poorer quality mirrors (series B). Simulation of SAXS data provides roughness parameters of the internal interfaces. For the better mirrors, the lateral correlation length of the roughness does not exceed 13 nm. However, this length is about 50 nm for the poorer quality mirrors, in agreement with AFM data.

The work is an experimental study of optical spin polarization in InAs/GaAs quantum dots (QDs) with 2 resident electrons or holes. A capture of a photo-generated electron-hole pair into such a QD creates a negative or positive tetron (double-charged exciton). Spin polarization was registered by the circular polarization of the QD photoluminescence (PL). The spin state was found to differ radically in the dots with opposite in sign charge. Particularly, under excitation in a GaAs barrier, the ground state PL polarization is negative (relative to the polarization of an exciting light) in the negatively charged QDs and positive in the positively charged QDs. With increasing excitation intensity, the negative polarization rises from zero up to a saturation level, while the positive polarization decreases. The negative polarization increases in weak magnetic fields applied in Faraday geometry, but strong fields suppress it. The positive polarization always increases as a function of magnetic field. We propose a theoretical model that qualitatively explains the experimental results. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier escape from self-organized InAs quantum dots (QDs) embedded in GaAs is studied by time-resolved capacitance spectroscopy. Thermal activation energies of 82 meV and 164 meV are determined for electrons and holes, respectively. We observe electron tunneling from the QD ground state and, at elevated temperatures, thermally activated tunneling from excited states. For holes, thermal activation from the QD ground state to the GaAs valence band is identified. We find good agreement with predictions of the level structure by eight-band k · p theory. The capture cross sections of ≈5 × 10—12 cm2 for holes and ≈3 × 10—12 cm2 for electrons correspond to the lateral size of the QDs.

A method for the growth of high‐quality gallium oxide (β‐Ga2O3) bulk crystals from the melt is developed. The influence of the atmosphere in the process zone on the stability of growth and the quality of Czochralski grown crystals is studied. The structural properties of the crystals obtained are investigated. Samples of gallium oxide substrates are demonstrated. The possibility of growing bulk crystals of solid‐solution oxides (AlxGa1–x)2O3is tested. Power electronics device performance improving is possible through the utilization of advanced materials, the most promising of which are β‐Ga2O3and β‐(AlxGa1–x)2O3. Herein, the results of the development of technology for obtaining high‐quality β‐Ga2O3crystals for substrates formation and further device design are presented.

Abstract: Capacitance- and conductance-voltage studies have been carried out on Schottky barrier structures containing a sheet of self-organized InAs quantum dots. The dots are formed in GaAs n-type matrices after the deposition of four monolayers of InAs. Quasi-static analysis of capacitance-voltage measurements indicates that there are at least two filled electron levels in the quantum dots, located 60 and 140 meV below the GaAs conduction band edge. The conductance of the structure depends on the balance between measurement frequency and the thermionic emission rate of carriers from the quantum dots. An investigation of the temperature-dependent conductance at different frequencies as a function of the reverse bias allows us to study separately the electron emission rates from the ground and first excited levels in the quantum dots. We estimate that the electron escape times from both levels of the quantum dots become comparable at room temperature and equal to about 100 ps.

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We report a novel approach for metal organic vapor phase epitaxy of (Al)GaN heterostructures on Si substrates. An approximately 90–100 nm thick SiC buffer layer is synthesized using the reaction between Si substrate and CO gas. High‐resolution transmission electron microscopy reveals sharp crystalline interfaces with epitaxial relationship between SiC/Si and AlN/SiC layers. Optimization of SiC morphology and AlN seed layer thickness facilitates the growth of GaN layers free of pits (v‐defects). It is also found that Si doping eliminates these defects in the case of growth on SiC templates with non‐optimized surface morphology. Thus, synthesis of thin SiC buffer layer is suggested as a solution for the interface problems at the initial stage of III‐N on Si epitaxy.