Persons

Николай Иванович Боргардт
Dr. Sci. (Phys.¬-Math.), Prof., Director of the Institute of Physics and Applied Mathematics, Head of the Research Laboratory of Electron Microscopy Studies, National Research University of Electronic Technology (Russia, 124498, Moscow, Zelenograd, Shokin sq., 1)

Article author

Metal nanoparticles are promising objects of research, since their properties are significantly different from the bulk material. When analyzing nanoparticles, it is important to study their size, stability, structural features and spatial arrangement. The initial and annealed nanoparticles of silver, formed on a carbon substrate by vacuum-thermal evaporation and having dimensions from 2 nm up to 10 nm, have been studied by using the high resolution electron microscopy method. The classification of their form and structure has been carried out. Among the studied ones the nanoparticles in the shape of a faceted ellipsoid with a polycrystalline structure, coarse nanoparticles with a monocrystalline structure and twins, icosahedral and decahedral nanoparticles with multiple twinning, and also, small single crystalline nanoparticles with dimensions less than 3.5 nm, have been revealed. It has been found that a result of annealing the number of small nanoparticles has been about 2 times decreased and the fraction of nanoparticles with icosahedral and decahedral shapes has been approximately 1.5 times increased. It has been shown that the nanoparticles with sizes less than 5 nm are unstable after a few seconds of exposure to high-energy electrons. For small initial and annealed single crystalline nanoparticles of less than 3 nm size the mean values of the lattice constant have been found by the precise determination of the atomic column centers on their images and the calculation of the local interplanar spacing values between the atoms located in mutually orthogonal (200) and (022) planes. It has been shown that in such nanoparticles both prior and after annealing there had been no noticeable distortions of the crystal structure and their lattice constant had been close to the value, characteristic for bulk silver.

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To create memory cells of new generation, epitaxial layers of GeSbTe (GST) material, with high crystalline perfection, and multilayered crystalline structures based on GeTe/SbTe superlattices grown on Si-wafers are of interest. This initiates the study of these and alike materials generation patterns, including with the involvement of molecular beam epitaxy. In this work, the structure of 13 nm thick layers of GST material, used to create phase-change memory cells was studied. These layers were grown on an Sb-passivated Si(111) substrate by molecular beam epitaxy. Research studies were carried out by transmission electron microscopy and electron diffraction analysis. Using high-resolution images of cross-sectional samples and diffraction patterns from planar thin foils, it was revealed that the layer consists of crystalline grains, mostly hexagonal, and in some local regions of the vacancy ordered cubic GST phase with the GST(0001) and GST(111) planes parallel to the Si(111). Based on an analysis of the moiré pattern appearing in bright-field electron microscopy images, it was found that the misorientation of the grains of the epitaxial layer around the Si(111) direction varies from 0 to 13.5º, and nearly 26 % of the surface area is almost non-rotated grains. Grains rotates within the angles from 0.2 to 2º occupy about 34 % of the layer surface area, from 2 to 8º occupy about 33 %, and the fraction of the area of grains rotated by more than 8º is close to 7 %. It has been found that as the rotation angle of the GST grains relative to the substrate increased, their average lateral size decreased from about 150 nm for non-rotated grains to 80 nm for grains rotated at an angle of more than 8º, and the average value of the rotation angle was approximately 2.6º. The data obtained on the grain structure of the epitaxial layer indicate that the relaxation of the misfit stresses of the crystal lattices of silicon and the GST material is provided both by the rotation of grains and, apparently, by the formation of misfit dislocations.

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The results of electron microscopy studies of a thin epitaxial aluminum layer on a misoriented gallium arsenide substrate are presented. It has been found that the layer consists of differently oriented domains and their crystal lattices coherently conjugate with the substrate forming misfit dislocations at the interface, as in the case of the layer grown on a singular substrate. Atomic steps on the substrate surface have been visualized and their influence on the growth of aluminum domains have been discussed.

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The results of the electron microscopy studies of a thin InAlAs epitaxial layer on the GaAs(100) substrate have been reported. The misfit dislocations at the heterointerface have been revealed, however, a residual strain has been found to exist in the layer, which distorts its lattice. By measuring the layer lattice parameters along the growth direction and perpendicular to it away from the misfit dislocations, the nominal lattice parameter has been locally calculated and the indium content has been found.

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