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Evolution of the reaction zone on the nanoscale has been studied in bi- and multilayered Co/a-Si as well as in trilayered Co/a-CoSi/a-Si and Co/CoSi/a-Si thin film diffusion couples. The kinetics of the phase boundary movement during solid state reaction has been followed with special interest of the initial stage of the diffusion, i.e. effects happening on the nanoscale (short time, short distance). The interfacial reactions have been investigated in situ by synchrotron radiation. The formed phases were also characterized by transmission electron microscopy and resistance measurements. The effect of phase nucleation and shift of phase boundaries have been separated in order to determine the “pure” growth kinetics of the crystalline CoSi and Co2Si product phases at the very early stages. Deviations have been found from the traditional diffusion controlled parabolic phase growth. Computer simulations based on a kinetic mean field model illustrated that the diffusion asymmetry (large difference in diffusion coefficients of the materials in contact) may offer a plausible explanations for this. [ABSTRACT FROM AUTHOR]

Abstract: Titanium dioxide films were grown on Re(10−10) by Ti vapor deposition in oxygen at T =830K and studied by means of low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS) and X-ray diffraction (XRD). The Ti oxide stoichiometry was determined by XPS as Ti:O=1:2, with the Ti oxidation state (4+). The TiO2 growth was monitored by means of LEED as a function of film thickness. Extending the coverage from the submonolayer into the multilayer regime gives rise to a p(2×2) pattern, a (poorly ordered) (1×1), and, finally, a stable (2×2) structure, the latter being associated with a homogeneous TiO2 phase. For normal electron incidence, the (2×2) LEED pattern exhibits systematically extinguished beams at (n ±1/2,0) positions, indicating a glide mirror plane. The pg(2×2) structure could be explained by both a rutile(011)-(2×1) reconstructed surface and a bulk truncated brookite(001) surface. Faceting phenomena, i.e. running LEED spots, observed with thin TiO2 films point to the formation of a rutile(011)-(2×1) surface with two domains and {011}-(2×1) facets and rule out the brookite alternative. Confirmation of this assignment was obtained by an XRD analysis performed at the Berlin synchrotron facility BESSY. [Copyright &y& Elsevier]