SILICIDE FORMATION AT PALLADIUM SURFACES - PART I - CRYSTALLINE AND AMORPHOUS SILICIDE GROWTH AT THE PD(110) SURFACE

Si adsorption and silicide formation at the Pd(110) surface is studied by scanning tunneling microscopy and vibrational spectroscopy of adso rbed CO. The CO stretch vibration is shown to be sensitive to the loca l bonding arrangement on the heterogeneous Si/Pd(110) surface. Silicid e growth shows a rich temperature-dependent behavior determined by the competition between interdiffusion and chemical reaction. At low temp eratures (T<140 K), amorphous Si is grown on the surface. Above this t emperature, silicide formation is observed. Initially amorphous silici de clusters and above 320 K well-shaped crystalline silicide islands a re formed. The growth mode of the silicide is of the Stranski-Krastano v type at T greater than or equal to 500 K. The crystalline silicide i s found to be a metastable phase of Pd,Si. The grown silicide is unsta ble at elevated temperatures and decays with lifetimes varying from se veral minutes to hours. A structural model for the crystalline silicid e is presented. (C) 1998 Elsevier Science B.V. All rights reserved.