Elshan Aziz Akhadov

Investigation of the morphology of the initial growth of the aromatic molecule p-quaterphenyl on NaCl (001)

Investigations of the structural properties of the initial layers of p-quaterphenyl (p-4P) vapor deposited onto NaCl (001) have been carried out using atomic force microscopy (AFM), grazing incidence x-ray diffraction (GIXRD), and helium atom scattering (HAS). A series of AFM images reveal accumulations of p-4P molecules around surface defects. Film thicknesses determined from height analyses of these images are in reasonable agreement with those found using GIXRD. The GIXRD studies indicate that p-4P films vapor-deposited at ambient temperature are composed of crystallites oriented with the long molecular axis nearly perpendicular to the NaCl (001) surface. For a nominally three-monolayer film, the b axis of the crystallites appears preferentially oriented along the substrate’s [110] azimuth, but with increasing thickness the x-ray features resemble those from two-dimensional (2D) powders. The diffraction peaks found in the HAS investigation at ∼50 K for a thick film grown at ∼200 K are similarly consist...

Surface structure of niobium-doped potassium tantalate KTa1 − xNbxO3 obtained from helium atom scattering studies

Helium atom scattering experiments have been carried out on the (001) surface of KTaO(3) doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diffraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (2 × 1) domains after thermally cycling the surface temperatures, and the distribution of step heights of terraces at the surface as multiples of the unit cell dimension of ∼ 4 Å. In addition, a large hysteresis effect was found in the (100) azimuth in the variation of surface reflectivity with surface temperature; a much smaller hysteresis effect was found in the (110) azimuth. The hysteresis effects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diffraction intensities near the surface temperature 80 K were also observed.