Two-Dimensional Surface Adatom of Gas Phase and Core-Level Photoemission Spectroscopy

Abstract

Si(111)√3×√3-Ag surfaces, prepared under various annealing conditions, was systematically investigated by scanning tunneling microscopy (STM) and reflection-high-energy electron diffraction (RHEED). Although the RHEED patterns were seemingly the same for all cases, the STM images showed clear difference in surface morphology and local structures at steps; step edges were roundish and decorated by random adsorption of clusters when annealed below 600oC. However, the steps were straight with periodic protrusions along them by higher-temperature and prolonged annealing, due to a formation of very narrow domains of 6×1-Ag structure at step edges. Such distinctions may be the origin for different results in core-level photoemission spectroscopy (CLPES). Since it is known that two-dimensional adatom gas (2 DAG) phase of excess Ag atoms exits on terraces, which changes the band bending in the substrate, the step edges (and clusters adsorbed there) may play as reservoirs of the 2 DAG. For the samples without sufficient annealing, the concentration of 2 DAG and the resulting band bending are inhomogenous over the sample surfaces, which make the CLPES spectra broaden. Sufficient annealing removes the reservoirs and 2 DAG, resulting in a homogenous band bending over the surfaces to get very sharp CLPES spectra.