Chlorine-induced restructuring of the Cu/Si(111) surface

Abstract

Chlorine-induced restructuring processes on Cu/Si(111) ``5\ifmmode\times\else\texttimes\fi{}5'' surfaces were studied with Auger electron spectroscopy and scanning tunneling microscopy techniques. The copper Auger signal intensities from these surfaces (each with different chlorine exposures and subsequent 450 \ifmmode^\circ\else\textdegree\fi{}C annealing), decreased with increasing initial chlorine exposures. At a Cl-coverage equal to \ensuremath{\sim}1 ML (after annealing) the Cu signal decreased below the detection limit. The associated restructuring processes were also explored. Initially homogeneous Cu/Si(111) ``5\ifmmode\times\else\texttimes\fi{}5'' surfaces, with Cl-exposures and annealing, separate into coexisting areas of Cu-free Cl/Si(111) 1\ifmmode\times\else\texttimes\fi{}1 and nearly chlorine-free areas of Cu/Si(111) ``5\ifmmode\times\else\texttimes\fi{}5.'' The original copper density is conserved by formation of three-dimensional ${\mathrm{Cu}}_{3}\mathrm{Si}$ crystallites on the surface. The restructuring is completely reversible; upon desorption of all chlorine at \ensuremath{\sim}600 \ifmmode^\circ\else\textdegree\fi{}C the surface resumes its original Cu/Si(111) ``5\ifmmode\times\else\texttimes\fi{}5'' structure. Possible implications for the atomic scale mechanisms in the direct synthesis of methylchlorosilanes from Cu/Si surfaces are discussed.