The dislocation structure of an AlN layer grown on a SiC substrate by sublimation was studied using transmission electron microscopy. The peculiarity of the growth method was the evaporation of the substrate during the growth of the layer to prevent its cracking. The purpose of the study was to identify the sources of threading dislocations in the AlN layer. Dislocation superjogs, which are sources of dislocations, were found in the layer. A connection between the formation of superjogs and the procedure of substrate evaporation is assumed.

Structural features of the interface between a semipolar gallium nitride layer and buffer layer of aluminum nitride grown on a SiC/Si(001) template misoriented by an angle of 7° were studied by high-resolution transmission electron microscopy. The effect of interface morphology on the structural quality of the gallium nitride layer was revealed: faceted structure of the buffer layer surface reduces the threading dislocations density.

Structural features of the interface between semipolar gallium nitride layer and buffer layer of aluminum nitride grown on a SiC/Si(001) template misoriented by an angle of 7° were studied by high-resolution transmission electron microscopy. The effect of interface morphology on the structural quality of the gallium nitride layer is revealed: faceted structure the surface of the buffer layer reduces the threading dislocations density.

A detailed study of the structure of a short-period superlattice based on alternating layers of cadmium and calcium fluorides grown by molecular beam epitaxy on a silicon substrate (111) by transmission electron microscopy and X-ray diffractometry has been performed. It has been established that the superlattice is in a pseudomorphic state and a lateral inhomogeneity with a fragment size of 10–40 nm has been found. The reason for the broadening of the main and satellite peaks of the superlattice on the diffraction curve (111) has been elucidated.

A detailed study of the structure of a short-period superlattice based on alternating layers of cadmium and calcium fluorides, grown by molecular beam epitaxy on a Si (111) substrate, by transmission electron microscopy and X-ray diffractometry, has been carried out. It was found that the superlattice is in a pseudomorphic state, and a lateral inhomogeneity with a fragment size of 10 - 40 nm was found. The reason for the broadening of the main and satellite peaks of the SL on the (111) diffraction curve has been clarified.

Dentin in the human tooth is a natural composite material with a complex multilevel hierarchical structure and consists of micro and nanostructures that are related to each other in a complex interrelation governed by laws that have not been fully understood yet. To identify the relationship between the dentin structure and its mechanical properties, we study samples prepared from human molars after subjecting them to uniaxial compression. Elements of dentin matrix and microtubules passing through it are investigated by transmission electron microscopy and computed microtomography using synchrotron light. Some structural features arising from the interaction between the elements and the dentin tubule properties that lead to arrest of crack propagation are investigated. We develop a theoretical model that can be used to identify the conditions for mode II crack inhibition due to opening of satellite cracks by stresses present on the surface of dentin tubules.

Dentin of human teeth is a natural composite material with a layered hierarchical structure; it is formed by micro- and nanostructures whose complex relations obey the laws not yet fully understood. In order to understand the effect of the dentin structure on its mechanical properties, a study of dentin samples prepared from human molars and subjected to a uniaxial compression was made. Synchrotron X-ray microtomography and transmission electron microscopy were employed to investigate the elements of dentin matrix and the tubules which cross the matrix. Single structural features based on the interaction of the elements, as well as the properties of the dentinal tubules, which can stop crack propagation have been investigated. A model is proposed for calculating the conditions of stopping of a mode II crack by generation of secondary cracks caused by the stresses over the surfaces of the tubules.

An array of CuO nanowhiskers have been fabricated by heating of copper coatings formed on stainless steel mesh substrate in air. Cross-sections of the nanowhiskers were studied by transmission electron microscopy. It was established that whiskers consist of two or more grains with incoherent boundaries. The mechanism of the formation of incoherent boundary is revealed. An important role of the incoherent boundaries in the formation of the nanowhiskers is discussed.

By transmission electron microscopy are studied two buffer structures based on AlGaN alloys doped with silicon and don't. The structures were grown on (111) orientated Si substrates by metal-organic vapour-phase epitaxy with consistently decreasing Al content. It is found that noticeable threading dislocation density reduction took place in intermediate layers at changing Al concentration from 32 to 23%. A phase decay and a composition modulation in growth direction in AlGaN layers with Al content 32, 23, 12 and 4% are observed. A model of the layers structure in the composition modulation area is proposed.

The results of transmission electron microscopy study and X-ray diffraction analysis of AlN/c Al2O3 templates with GaN ultrathin insertions grown by plasma-assisted molecular beam epitaxy are presented. It is shown that AlN buffer layers with faceted surface morphology provide a much higher threading dislocations density reduction then with smooth layers. The filtering action of ultrathin GaN insertions is confirmed.

Two buffer structures based on Al x Ga 1 – x N solutions with silicon doping and without it have been studied by transmission electron microscopy. The structures have been grown on silicon substrates with the (111) orientation by metalorganic vapor-phase epitaxy with consistently decreasing Al content. A significant threading dislocation density reduction in the region of intermediate layers has been found at a change in the Al content from 32 to 23%. Phase decay and the phenomenon of compositional self-modulation in the Al x Ga 1 – x N layers in the direction of growth have been detected at an Al content equal to 32, 23, 12, and 4%. A model of the structure of layers in the region of composition modulation has been proposed.

We present the results of a transmission electron microscopy and X-ray diffractometry investigation of AlN/ c -Al 2 O 3 templates with GaN ultrathin insertions grown by plasma-assisted molecular beam epitaxy. It has been shown that AlN buffer layers with faceted surface morphology provide a greater threading dislocation density reduction than smooth layers. The filtering effect of GaN ultrathin insertions has been confirmed.

The interaction between a+c-type and a-type dislocations in thick (up to 14 µm) semipolar GaN layer grown by hydride vapor phase epitaxy on a 3C SiC/Si(001) template has been detailed investigated by means of transmission electron microscopy. It is shown, that the expansion of a dislocation half loop with Burgers vector b=1/3<1-210> during cooling process can be blocked by its reaction with a threading dislocation with b=1/3<1-210> to form a dislocation segment with b=<0001>. This dislocation reaction is discussed in terms of the energy relaxation. The approximation estimate made within the linear tension approach gives the total energy gain ~7.6 eV/Å (that is, in general, ~45.6 keV for the observed screw dislocation segment of length 600 nm formed as a result of the reaction). Using the core energy calculations, the dislocation core contribution was also estimated as ~19.1 keV.

Transmission electron microscopy was used to study the interaction of a + c and a dislocations in a thick (14 μm) semipolar GaN layer grown by hydride vapor phase epitaxy on a 3C-SiC/Si(001) template. It is shown that the propagation of a dislocation half-loop with a Burgers vector b = $$\frac{1}{3}\left\langle {1\bar {2}10} \right\rangle $$ during cooling can be blocked due to its reaction with a threading dislocation with a Burgers vector b = $$\frac{1}{3}\left\langle {\bar {1}2\bar {1}3} \right\rangle $$ with the formation of a dislocation segment with a Burgers vector b = 〈0001〉. The gain in energy of the system as a result of such reaction is theoretically estimated. Within the approximation of dislocation linear tension, this gain is ~7.6 eV/Å, which gives ~45.6 keV for new dislocation segment with a length of ~600 nm. The contribution of the energy of the dislocation core is estimated as ~19.1 keV.

The defect structure of a thick (~15 μm) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.

Bulk nanocomposites based on superconducting metals Pb and In embedded into matrices of natural chrysotile asbestos with the nanotube internal diameter d ~ 6 nm have been fabricated and studied. The low-temperature electrical and magnetic properties of the nanocomposites demonstrate the superconducting transition with the transition critical temperature Tc ≈ (7.18 ± 0.02) K for the Pb–asbestos nanocomposite (this temperature is close to Tc bulk = 7.196 K for bulk Pb). The electrical measurements show that In nanofilaments in asbestos have Tc ~ 3.5–3.6 K that is higher than Tc bulk = 3.41 K for bulk In. It is shown that the temperature smearing of the superconducting transition in the temperature dependences of the resistance R(T) ΔT ≈ 0.06 K for the Pb–asbestos and ΔT ≈ 1.8 K for the In–asbestos are adequately described by the fluctuation Aslamazov–Larkin and Langer–Ambegaokar theories. The resistive measurements show that the critical magnetic fields of the nanofilaments extrapolated to T = 0 K are Hc(0) ~ 47 kOe for Pb in asbestos and Hc(0) ~ 1.5 kOe for In in asbestos; these values are significantly higher than the values for the bulk materials (H\(H_{\rm{c}}^{\rm{bulk}}\) = 803 Oe for Pb and \(H_{\rm{c}}^{\rm{bulk}}\) = 285 Oe for In). The results of the electrical measurements for Pb‒asbestos and In–asbestos agree with the data for the magnetic-field dependences of the magnetic moment in these nanocomposites.

AbstractBulk nanocomposites based on superconducting metals Pb and In embedded into matrices of natural chrysotile asbestos with the nanotube internal diameter d ~ 6 nm have been fabricated and studied. The low-temperature electrical and magnetic properties of the nanocomposites demonstrate the superconducting transition with the transition critical temperature T _c ≈ (7.18 ± 0.02) K for the Pb–asbestos nanocomposite (this temperature is close to T _c bulk = 7.196 K for bulk Pb). The electrical measurements show that In nanofilaments in asbestos have T _c ~ 3.5–3.6 K that is higher than T _c bulk = 3.41 K for bulk In. It is shown that the temperature smearing of the superconducting transition in the temperature dependences of the resistance R ( T ) Δ T ≈ 0.06 K for the Pb–asbestos and Δ T ≈ 1.8 K for the In–asbestos are adequately described by the fluctuation Aslamazov–Larkin and Langer–Ambegaokar theories. The resistive measurements show that the critical magnetic fields of the nanofilaments extrapolated to T = 0 K are H _ c (0) ~ 47 kOe for Pb in asbestos and H _ c (0) ~ 1.5 kOe for In in asbestos; these values are significantly higher than the values for the bulk materials ( H $$H_{\rm{c}}^{\rm{bulk}}$$ H c b u l k = 803 Oe for Pb and $$H_{\rm{c}}^{\rm{bulk}}$$ H c b u l k = 285 Oe for In). The results of the electrical measurements for Pb‒asbestos and In–asbestos agree with the data for the magnetic-field dependences of the magnetic moment in these nanocomposites.

This paper presents the results of a detailed study of the structure of nanowhiskers (NWs) of copper oxide formed in the process of thermal oxidation. It is shown that NWs have a bi- or poly-crystalline structure with a growth direction [110]. It is noted that the formation of NWs is facilitated by the cooperation of internal stresses with the defective structure of the underlying coating, and they grow owing to surface diffusion of copper cations from the depth of the coating to the top of the whisker. It is established that NWs have a good sorption and photocatalytic ability that will allow their use in the chemical industry, including the areas of catalysis and photocatalysis.

AbstractThe defect structure of a thick (~15 μm) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.

Initial stages of the semipolar AlN layer formation by chloride-hydride vapor phase epitaxy on a misoriented Si(100) substrate with a thin intermediate nano-SiC layer grown by atomic substitution method are investigated. It is found that once the growth rate of AlN layer on a nano-SiC/Si(100) substrate is about 0.02 μm/h, the layer is formed in a polar direction. On the other hand, at the growth rate of 1 μm/h the layer is formed in a semipolar direction. We propose the model of the semipolar AlN layer growth based on the formation of the special structure on the SiC layer synthesized by atomic substitution and on the possibility of the matching of the quasi-lattices of Al(20 − 23) and 3CSiC(100) planes assuming bonding of four atoms from the layer to four atoms of the 3CSiC quasi-lattice consisting of three lattice unit cells in one of the directions.