Silicide formation at palladium surfaces. Part I: Crystalline and amorphous silicide growth at the Pd(110) surface

Abstract

Si adsorption and silicide formation at the Pd(110) surface is studied by scanning tunneling microscopy and vibrational spectroscopy of adsorbed CO. The CO stretch vibration is shown to be sensitive to the local bonding arrangement on the heterogeneous Si/Pd(110) surface. Silicide growth shows a rich temperature-dependent behavior determined by the competition between interdiffusion and chemical reaction. At low temperatures ( T<140 K), amorphous Si is grown on the surface. Above this temperature, silicide formation is observed. Initially amorphous silicide clusters and above 320 K well-shaped crystalline silicide islands are formed. The growth mode of the silicide is of the Stranski–Krastanov type at T≥500 K. The crystalline silicide is found to be a metastable phase of Pd 2Si. The grown silicide is unstable at elevated temperatures and decays with lifetimes varying from several minutes to hours. A structural model for the crystalline silicide is presented.