SIMS STUDY OF THE INTERACTION OF METHANOL WITH CLEAN CU(100)

The interaction of MeOD (=M) with the clean Cu(100) surface at similar to 125 K was examined by low-flux (static) SIMS. The molecular charac ter of the adsorption process was evident in the structure of the majo r secondary ion progressions detected, namely CuM(n)(+) M(n)D(+), M(n) OD(-) and M(n)MeO(-) (n=0,1,...). Above similar to 0.6 L exposure, MeO D adsorption was found to be spontaneously reversible and dependent on the partial pressure of MeOD. At this same exposure a threshold for e nhanced emission of OH- (relative to OD-) and the larger secondary ion clusters was reached. It is suggested that typical MeOD condensation on Cu(100) proceeds initially by dispersion of an isolated dimeric spe cies, rather than by nucleative growth as polymeric clusters, and that the similar to 0.6 L exposure threshold marks the onset of lateral in ter-site adsorbate interactions, which are apparently repulsive in cha racter. For MeOD partial pressures in excess of 5 x 10(-8) mbar, a pre ferential attenuation of the yields of all clusters containing Cu take s place, which is attributed to multilayer MeOD condensation.