Structure determination of Au on Pt(111) surface:LEED, STM and DFT Study

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distance between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacing of the clean Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed

Determination of the crotonaldehyde structures on Pt and PtSn surface alloys from a combined experimental and theoretical study

International audienceA complementary experimental and theoretical study of the alloying effects of Sn on the molecule–surface bonding of crotonaldehyde on Pt(111) is presented. By comparing high-resolution electron energy loss spectroscopy (HREELS) data and density-functional theory (DFT) calculations of vibrational spectra from a complete set of possible adsorption configurations of crotonaldehyde on the Pt(111) and Pt2Sn(111) surfaces, we are able to identify the adsorption structures present on the surface. An interpretation of the HREELS spectra for these highly complex systems is proposed and the effect of alloying with Sn on the molecule–surface interactions is addressed

Recrystallization of highly-mismatched BexZn1–xO alloys : formation of a degenerate interface

We investigate the effect of thermally induced phase transformations on a metastable oxide alloy film, a multiphase BexZn1–xO (BZO), grown on Al2O3(0001) substrate for annealing temperatures in the range of 600–950 °C. A pronounced structural transition is shown together with strain relaxation and atomic redistribution in the annealed films. Increasing annealing temperature initiates out-diffusion and segregation of Be and subsequent nucleation of nanoparticles at the surface, corresponding to a monotonic decrease in the lattice phonon energies and band gap energy of the films. Infrared reflectance simulations identify a highly conductive ZnO interface layer (thicknesses in the range of ≈10–29 nm for annealing temperatures ≥800 °C). The highly degenerate interface layers with temperature-independent carrier concentration and mobility significantly influence the electronic and optical properties of the BZO films. A parallel conduction model is employed to determine the carrier concentration and conductivity of the bulk and interface regions. The density-of-states-averaged effective mass of the conduction electrons for the interfaces is calculated to be in the range of 0.31m0 and 0.67m0. A conductivity as high as 1.4 × 103 S·cm–1 is attained, corresponding to the carrier concentration nInt = 2.16 × 1020 cm–3 at the interface layers, and comparable to the highest conductivities achieved in highly doped ZnO. The origin of such a nanoscale degenerate interface layer is attributed to the counter-diffusion of Be and Zn, rendering a high accumulation of Zn interstitials and a giant reduction of charge-compensating defects. These observations provide a broad understanding of the thermodynamics and phase transformations in BexZn1–xO alloys for the application of highly conductive and transparent oxide-based devices and fabrication of their alloy nanostructures