Epitaxial growth of thin Ag and Au films on Si(111) using thin copper silicide buffer layers

Abstract

Synchrotron radiation photoemission experiments show that a thin copper silicide layer formed by depositing the equivalent of six layers of Cu on Si(111) serves as an excellent buffer for additional growth of Ag and Au overlayers. Introduction of this buffer below a Ag film leads to enhanced quantization effects in the valence band spectra and the appearance of a Ag(111) surface state. Without the buffer layers this surface state shifts above the Fermi level due to strain in the film. Strong coupling is observed between the quantized Ag sp band and the Cu d band but the coupling to the Cu sp band found for Ag on bulk Cu is absent. In the case of Au overlayers the copper silicide layer prevents the reaction between Si and Au that otherwise results in the formation of a reacted layer on top of the Au film. Introduction of the buffer layer leads to Au film properties characteristic of the (111) surface such as a surface component in the core level spectra and a surface state just below the Fermi level.