Measurement of distribution of charge adsorbed on Au<i>_x</i>/Si(111)-7×7 surface on an atomic scale in ultra-high vacuum

Abstract

The physicochemical properties of Au atoms adsorbed on the surface on an atomic scale play a very important role in preparing nanodevices and surface catalysis. In this paper, we use frequency modulated Kelvin probe force microscopy (FM-KPFM)to study the multi-bit adsorbed charge distribution of Au on the surface of Si(111)-(7×7) at room temperature. Firstly, the surface topography and local contact potential difference (LCPD) of Au at different adsorption sites in Si(111)-(7×7) are successfully obtained by using home-made ultra-high vacuum Kelvin probe force microscopy. Secondly, we analyze the atomic characteristics of specific atomic positions of Au/Si(111)-(7×7) by force spectroscopy and potential difference, and realize the atomic identification . The adsorption characteristics of Au/Si(111)-(7×7) surface charge transfer and Au are explained by combining differential charge density calculations. The results show that Au atom adsorption mainly is in the form of single atom and cluster . Specifically, the Au cluster is adsorbed at the three central positions of Si(111)-(7×7) in a hexagonal structure of six atoms. Individual Au atoms are adsorbed to the positions of central adatoms of Si(111)-(7×7). At the same time, through the measurement of potential difference, it is known that a single Au atom and Au cluster lose electrons, presenting a positive electrical characteristic. The results of surface differential charge density show that Au undergoes charge transfer during adsorption, losing part of the charge, which locally reduces the work function at the position of the adsorbed atom. In the range of distances where short-range forces, local contact potential energy differences and differential charge densities change, the theoretical results and experimental results are in reasonable agreement.