A. E. Kalmykov

Electron-microscopic investigation of a SiC/Si(111) structure obtained by solid phase epitaxy

First results of the electron-microscopic investigation of thin silicon carbide (SiC) layers grown on silicon using a new method of solid phase epitaxy are presented. It is shown that, at the initial stage of epitaxial growth, a transition layer is formed which consists of various SiC polytypes. This layer occurs at the interface between the substrate and a single-crystalline SiC layer possessing predominantly a 3C polytype structure. It is established that pores with dimensions ranging from a fraction of micron to several dozen nanometers are formed in a near-surface layer of the silicon substrate, which favor the growth of epitaxial, weakly strained single-crystalline SiC layers.

Structural characterization of GaN epilayers on silicon: Effect of buffer layers

Cross-sections of GaN/AlN/3C-SiC/Si(111) system have been studied by electron microscopy techniques. A nanometer thick buffer layer of silicon carbide on Si(111) substrate was formed using an original solid-phase epitaxy method. The subsequent layers of gallium nitride and aluminum nitride were grown by the method hydride-chloride vapor phase epitaxy. The resulting GaN layers display neither threading dislocations nor cracks on any scale. The main fraction of defects in GaN layers have the form of dislocation pileups that are localized at and oriented parallel to the GaN/AlN interface. The dislocation density in the obtained GaN layers is (1–2) × 109 cm−2, which corresponds to a minimum level reported in the available literature. The buffer AlN layer contains nanopores, which reduce the level of stresses at the GaN/AlN interface and thus almost completely inhibit the formation of threading dislocations.

Structural properties and current transport in a nanocomposite formed on a silicon surface by oxidation of the porous layer

The possibility of obtaining a Si-SiO2 nanocomposite layer by oxidation of porous silicon is demonstrated. The nanocomposite thus prepared consists of silicon oxide with inclusions of crystalline silicon in the form of rounded particles 5 to 30 nm in diameter and a filamentary cellular structure with filaments a few nanometers thick. The I-V characteristics of these structures were measured under different sample excitation conditions (photo-and thermal stimulation). The trap concentration and effective carrier mobility are estimated. Carriers are found to be captured intensely by traps created in the large-area interface in the composite structure.

Features of the current-voltage characteristics and temperature dependences of electric conductivity in porous silicon layers

A method of separating porous silicon (por-Si) layer without deformation from a silicon substrate, which virtually excludes almost any risk of subsequent degradation of the isolated por-Si layer is proposed. The current-voltage characteristics of por-Si have been measured in a temperature interval of 300–255 K. Direct measurements of the conductivity of por-Si have been performed for the first time and it is established that the conductivity has an activation nature for the current passage parallel to the por-Si sample surface.

X-ray diffractometry and electron microscopy of porous silicon layers at different stages of oxidation in air

Porous silicon layers prepared by anodic etching under different conditions have been systematically studied in the course of their natural oxidation (aging) in air by many-crystal X-ray diffractometry and transmission electron microscopy. Quantitative information on the strains and crystal structure of layers has been obtained using a combination of measurements of the 004 symmetric and 224 asymmetric reflections in the Bragg geometry on double-crystal and triple-crystal X-ray diffractometers. It has been revealed that the aging of porous silicon is accompanied by an increase in macrostrains and microstrains, as well as in micro-misorientations of crystal fragments, which lead to gradual destruction of porous layers up to their complete amorphization.

Electron-microscopic study of Sn-chrisotile asbestos nanocomposite

Transmission electron microscopy was used to study the structural state of tin in Sn-chrisotile asbestos nanocomposite. It is shown that tin in the nanocomposite forms a system of nanowires, which, in turn, consist of crystallites of different lengths. Various orientational relations between the matrix and crystallites are revealed.

Sequential structural characterization of layers in the GaN/AlN/SiC/Si(111) system by X-ray diffraction upon every growth stage

X-ray diffraction and transmission electron microscopy techniques have been used to study the dynamics of variation of the structural characteristics and deformation state in SiC, AlN, and GaN epilayers sequentially grown on a Si(111) substrate. In this system, the SiC layer has been grown by solid-phase epitaxy, while the AlN and GaN layers have been deposited by chloride-hydride vapor-phase epitaxy (HVPE) using argon as a carrier gas.

Laser-induced modification of porous silicon

We present the results of experiments on annealing the surface layer of porous silicon by pulsed IR laser radiation. The character of laser-induced modification has been studied using IR spectroscopy and transmission electron microscopy. It is shown that the proposed method can be used to obtain a Si:SiO2 composite.

Optical properties of metal nanoparticles in chrysotile channels

Chrysotile samples with macroscopically ordered channels filled by gold and silver have been studied using optical transmission spectroscopy. The channels had inner diameters below 5 nm and lengths up to about 1 cm. The transmission spectra of samples strongly depend on the polarization of probing light. The observed spectral properties are probably related to plasmon resonances of metal particles and to surface plasmon polaritons.

Size effects in electrical and magnetic properties of quasi-one-dimensional tin wires in asbestos

Bulk composites have been prepared based on one-dimensional fibers of natural chrisothil-asbestos with various internal diameters (d = 6–2.5 nm) filled with tin. The electrical and magnetic properties of quasi-one-dimensional Sn wires have been studied at low temperatures. The electrical properties have been measured at T = 300 K at a pressure P = 10 kbar. It has been found that the superconducting (SC) characteristics of the nanocomposites (critical temperature Tc and critical magnetic field Hc) increase as the Sn filament diameter decreases. The temperature spreading of the resistive SC transition also increases as the Sn filament diameter decreases, which is explained by the SC order parameter fluctuations. The size effects (the increase in critical temperature Tc and transition width ΔTc) in Sn nanofilaments are well described by the independent Aslamazov–Larkin and Langer–Ambegaokara fluctuation theories, which makes it possible to find the dependence of Tc of the diffuse SC transition on the nanowire diameter. Using the temperature and magnetic-field dependences of the magnetic moment M(T, H), it has been found that the superconductor–normal metal phase diagram of the Sn–asbestos nanocomposite has a wider region of the SC state in T and H as compared to the data for bulk Sn. The magnetic properties of chrisotil-asbestos fibers unfilled with Sn have been studied. It has been found that the Curie law is fulfilled and that the superparamagnetism is absent in such samples. The obtained results indicate the absence of magnetically ordered impurities (magnetite) in the chrisotil-asbestos matrix, which allowed one to not consider the problem of the interaction of the magnetic subsystem of the asbestos matrix and the superconducting subsystem of Sn nanowires.