Properties of Au film on Ru(0001) revealed by AES, LEED, and DEPES

Abstract

In this work the application of the surface sensitive experimental methods such as Auger electron spectroscopy, low energy electron diffraction, and directional elastic peak electron spectroscopy is shown to characterize the growth mode, the long and short range order of Au layers on the Ru(0001) surface. The adsorption was carried out at different substrate temperatures from room temperature till 460 °C. Auger signal from the substrate and the adsorbate recorded during the continuous Au adsorption indicates the formation of the first and then the second gold wetting layer at elevated substrate temperatures. At room temperature the formation of the second layer just before the completion of the first monolayer occurs. Further adsorption leads to the growth of three dimensional gold islands on 2 ML of Au on Ru(0001). At elevated temperatures the reduction of the Auger signal drop rate from the substrate and the signal rise rate from the adsorbate after the formation of 2 ML of Au can be rationalized by the coalescence of three dimensional Au islands and/or the decrease of the sticking coefficient of gold. Above 460 °C the saturation of Auger signals corresponding to 2 ML of Au is observed. The LEED pattern observations reveal the long range order within the clean and covered by about 5 ML of gold Ru(0001). The diffraction spots of the adsorbate reflect the Au(111) arrangement. The application of the DEPES method to the clean and covered by gold Ru(0001) surface reveals the presence of A and B type terraces on the Ru(0001) surface, as well as mutually rotated by 180° adsorbate domains, which exhibit the 12¯1111Au//01¯100001Ru and 1¯21¯111Au//01¯100001Ru orientations with respect to the crystalline substrate. The detailed R-factor analysis of experimental and theoretical DEPES distributions, the latter obtained with the use of the multiple scattering calculations, reveals equal population of A and B type Ru(0001) terraces, as well as unrotated and rotated Au(111) domains, which results in the six-fold symmetry DEPES intensity distributions for clean and covered substrate. The discussion of DEPES results concerns the adsorbate and substrate structures, inelastic mean free paths, and scattering properties of individual Au and Ru atoms described by the scattering factors and differential scattering cross sections.