Structural changes of MoS2 nano-powder in dependence on the annealing temperature

To search for structural changes of molybdenum disulphide (MoS₂) nano-powder under thermal treatment, the annealing of the powder was carried out in vacuum or in argon. MoS₂ powder with a grain size of 3–5 nm was synthesized by a chemical method. The temperature of annealing was varied in the range of 380–1000 °C. The time of annealing was varied in the range from 4 h (380 °C) to 5 min (1000 °C). X-ray diffraction and transmission electron microscopy analyses were made to see the character of the change of the crystallization process and the curvature of (002) MoS₂ planes. The increase of crystalline phase and the decrease of amorphous phase in the powder appears as a result of the rise of the annealing temperature. The sample annealed at T_ann=380 °C and 500 °C has a small curvature of (002) planes and more enlarged grains in comparison with non-annealed MoS₂ powder. The increase of the annealing temperature to T_ann=700 °C leads to a strong curvature of the (002) planes. The character of the curved planes varies from quite long planes with a large radius of curvature to right-angle-form and U-form structures. The increase of the annealing temperature to T_ann=1000 °C leads to a strong crystallization of the powder and a reduction of the amorphous phase. PACS 81.05.Tp; 81.07.Wx; 81.20.Ka; 61.10.-i; 68.37.Lp     

Formation of ultrasmall germanium nanoislands with a high density on an atomically clean surface of silicon oxide

The experimental results of an investigation into the initial stages of growth of a germanium film on an atomically clean oxidized silicon surface are reported. It is shown that the growth of the germanium film in this system occurs through the Volmer-Weber mechanism. Elastically strained nanoislands with a lateral size of less than 10 nm and a density of 2 × 10¹² cm^?2 are formed on the oxidized silicon surface. In germanium films with a thickness greater than 5 monolayers (ML), there also arise completely relaxed germanium nanoislands with a lateral size of up to 200 nm and a density of 1.5 × 10⁹ cm^?2.     

Role of the dislocation screw component in the formation of the dislocation structure in Ge- and Si-based semiconductor heterosystems

The possibility of solving the problem of propagating dislocations in heterosystems by means of decreasing the number of dislocation families participating in the process of misfit stress relief has been investigated. The system of Γ-shaped misfit dislocations, which is proposed in the literature as the optimal type of plastic relaxation, has been analyzed. Taking into account the effect of the screw dislocation component, this suggestion is valid only for the initial stage of relaxation. The results of simulation of the process of plastic relaxation and experimental investigations of structures containing L-shaped dislocations are presented. Misfit stress relief in heterostructures grown on vicinal substrates has been theoretically and experimentally investigated.     

Spontaneous composition modulation during Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te(301) molecular beam epitaxy

The spontaneous composition modulation of a solid solution in Cd _x Hg_1?x Te during molecular beam epitaxy at CdTe/ZnTe/GaAs(301) substrates has been discovered. The study of the micromorphology of the film surfaces in an atomic-force microscope, together with the study of the film microstructure in a transmission electron microscope, has revealed that a periodic system of macrosteps oriented along the [010] direction and separated by (100) terraces is formed during epitaxial growth at temperatures higher than the optimal value on a Cd _x Hg_1?x Te(301) surface. The growth of the film of homogeneous composition is only possible at the fronts of macrosteps and it is not possible at (100) terraces, where a layered structure grows with composition modulated along the [100] direction having period of several tens of angström. The observed phenomenon is explained by decreased adsorption of mercury atoms in the (100) plane.     

Analysis of the Properties of Metal Sulfide Nanocrystals Synthesized by the Langmuir—Blodgett Technique

JETP Letters - Nanocrystals of metal sulfides (CdS, ZnS, CdZnS, CuS, and PbS) are formed upon the interaction of gaseous hydrogen sulfide with Langmuir—Blodgett films of metal behenates. To...     

Effect of buffer layers on the dislocation structure of heteroepitaxial systems

Transmission electron microscopy (TEM) as well as X-ray topography (XRT) and X-ray diffractometry have been used for investigation of the structure of the LPE heteroepitaxial system In_0.05Ga_0.95As-In_yGa_1−yAs_1−xP_x-GaAs(111) A. A critical value of the lattice misfit has been shown to exist at the metallurgical boundary ((Δa/a)* ≈ 10⁻³) which results in the change of the film nucleation and growth mechanism as well as the change of misfit dislocations (MDs) generation mechanism. With (Δa/a)₀ > (Δa/a)* the nucleation and growth mechanism is mixed: island growth at the first stages of growth and layer-by-layer growth at large thicknesses. MDs are created in an “island film” developing a non-ordered dislocation network. The density of threading dislocations (N_d) is ∼ 10⁸ cm⁻². With (Δa/a)₀ < (Δa/a)* there is layer-by-layer mechanism of film's nucleation and growth from the very first stages of crystallization. MDs are injected into continuous layer along the inclined slip planes {111}, thus forming a regular three-dimensional grid of MDs. N_d is less than 10⁶ cm⁻² in the case. A model of dislocation structure formation in heterolayers has been proposed. Within the frame of this model the two critical values of phosphorus concentration in the quaternary melt have been quantitatively determined. These are corresponding to the change of MD generation mechanism. The expected values of N_d for (Δa/a)₀ > (Δa/a)* and (Δa/a)₀ < (Δa/a)* have been theoretically determined.