Articles you may be interested inIn situ observation of the elastic deformation of a single epitaxial SiGe crystal by combining atomic force microscopy and micro x-ray diffraction
Grazing incidence X-ray diffraction (GID) was employed to probe the structure of atomically thin carbon layers on SiC(0001): a so-called buffer layer (BL) with a 6( √ 3 × √ 3)R30 • periodicity, a monolayer graphene (MLG) on top of the BL, and a bilayer graphene (BLG). The GID analysis was complemented by Raman spectroscopy. The lattice parameter of each layer was measured with high precision by GID. The BL possesses a different lattice parameter and corrugation when it is uncovered or beneath MLG. Our results demonstrate that the interfacial BL is the main responsible for the strain in MLG. By promoting its decoupling from the substrate via intercalation, it turns into graphene, leading to a simultaneous relaxation of the MLG and formation of a quasi-free-standing BLG.
Growth of nanocrystalline graphene films on (6 √ 3 × 6 √ 3)R30 •reconstructed SiC surfaces was achieved by molecular beam epitaxy, enabling the investigation of quasi-homoepitaxial growth. The structural quality of the graphene films, which is investigated by Raman spectroscopy, increases with growth time. X-ray photoelectron spectroscopy proves that the SiC surface reconstruction persists throughout the growth process and that the synthesized films consist of sp 2 -bonded carbon. Interestingly, grazing incidence x-ray diffraction measurements show that the graphene domains possess one single inplane orientation, are aligned to the substrate, and offer a noticeably contracted lattice parameter of 2.450 Å. We correlate this contraction with theoretically calculated reference values (all-electron density functional calculations based 4 on the van der Waals corrected Perdew-Burke-Ernzerhof functional) for the lattice parameter contraction induced in ideal, free-standing graphene sheets by: substrate-induced buckling, the edges of limited-size flakes and typical point defects (monovacancies, divacancies, Stone-Wales defects).
Individual self-assembled SiGe/Si(001) dot molecules were investigated by scanning x-ray nanodiffraction with a beam size of 250 nm in diameter (full width at half maximum). The samples contain dot molecules with either one, two, three, or four dots. Different azimuthal configurations were measured and compared with simulated diffraction patterns. We have combined finite element calculations, kinematic scattering simulations, and experimental measurements to obtain information about lateral positional correlation as well as strain and germanium content within individual dot molecules.
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