SI-H BOND ACTIVATION ON CU - REACTION OF SILANE ON CU(111)

The activation and decomposition of silane on Cu(111) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on Cu(111) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH2 and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H, which themselves depend upon the silane exposure. SiH2 is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at approximately 330 K. Auger electron spectra show that the amount of silicon deposited on the Cu(111) surface in this way is approximately one-third of the amount deposited on a stable Cu3Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. The reactivity of a copper silicide surface toward silane was also studied. Silicon bearing copper surfaces are less reactive than is the parent clean surface. What reactions are seen lead to a variety of adsorbed silyl fragments including SiH3. It is believed that defects play a key role in these latter reaction pathways.