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The kinetics of the initial oxidation of Si(111)7 X 7 by 02 in the submonolayer regime was studied using laser-induced thermal desorption, temperature-programmed desorption, and Auger-electron spectroscopy. The results showed that the oxidation of Si(111)7X 7 by 02 was characterized by two kinetic processes. Initially, a rapid oxygen uptake step occurred that was followed by a slower growth process which asymptotically approached an apparent saturation oxygen coverage. The initial reactive sticking coefficient (S~) of 02 on Si(111)7X7 decreased with surface temperature from So =0.2 at 200 K to So =0.06 at 600 K. The observed decrease in So suggested that the initial oxidation of Si(111) 7X7 was mediated by an 02 precursor species. In contrast, the apparent saturation oxygen coverage was observed to increase as a function of surface temperature. The apparent saturation oxygen coverage increased from approximately 6=0.4 ML at 110 K to 6=0.7 ML at 600 K. Experiments with preadsorbed hydrogen also demonstrated that the initial reactive sticking coefficient for 0& and the apparent saturation oxygen coverage were reduced as a function of increasing hydrogen coverage on the Si(111)7X7 surface. This behavior indicated that the oxidation of Si(111)7 X 7 requires free dangling-bond sites.

The adsorption and desorption kinetics for SiCl 4 on Si ( 111 ) 7 X 7 were studied using laserinduced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. TPD experiments monitored SiCl 2 as the desorption product at approximately 950 K using a heating rate of {3 = 9 Kls. SiCl 2 was also observed as the desorption product in the LITO yield at all surface coverages. LITO measurements determined the initial reactive sticking coefficient (So) ofSiCl 4 on Si( 111)7 X 7 versus surface temperatu"e. The sticking coefficient was observed to decrease with surface temperature from So z 0.18 at 160 K to SozO.03 at 600 K. TPO experiments revealed that the chlorine surface coverage saturated after large SiCl 4 exposures and the saturation coverage was independent of surface temperature. Isothermal LITO studies enabled the surface chlorine coverage to be monitored as a function of time during SiCl 2 desorption. These studies revealed second-order desorption kinetics for SiCl 2 with a desorption activation barrier of Ed = 67 ± 5 kcallmol and preexponential OfVd = 3.2X lO o ±o.1 cm 2 /s. Experiments with preadsorbed hydrogen demonstrated that the initial sticking coefficient of SiCl 4 was reduced as a function of increasing hydrogen coverage. This behavior indicated that the adsorption of SiCl 4 on Si ( 111 ) 7 X 7 requires free surface dangling bonds. LITO techniques were also used to study the surface diffusion of the chlorine on Si( 111 )7X 7 after SiCl 4 adsorption. No evidence of significant surface chlorine mobility (D<2 X 10 ~ II cm 2 Is) was found for surface temperatures as high as 825 K..