AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM3
D Abstraction by H on Si(111) Surfaces: Temperature and Coverage Dependence

Monday, November 4, 2002, 9:00 am, Room C-108

Session: Adsorption and Chirality
Presenter: F. Khanom, Kyushu Institute of Technology, Japan
Authors: F. Khanom, Kyushu Institute of Technology, Japan
F. Rahman, Kyushu Institute of Technology, Japan
A. Aoki, Kyushu Institute of Technology, Japan
A. Namiki, Kyushu Institute of Technology, Japan
Correspondent: Click to Email
Influences of surface temperature T@sub s@ and D adatom coverage on direct abstraction (ABS) as well as collision-induced-desorption (CID) of surface D adatoms by H atoms have been studied on Si(111). We found that D@sub 2@ CID as a result of reaction H + D/Si --> D@sub 2@ , obeys a third-order kinetics with respect to @theta@@sub D@, ruling out the so-called hot atom mechanism. D@sub 2@ CID rate versus T@sub s@ curves were found to exhibit a close similarity in spectral line shape with a @beta@@sub2@ temperature-programmed-desorption (TPD) spectrum arising from a dideuteride phase. The spectral similarity between CID and TPD suggests that D@sub 2@ CID obey the same mechanism as for the @beta@@sub 2@ TPD. In order to understand the underling mechanism we measured reaction order of the @beta@@sub 2@ TPD. As a consequence, 1.5th-reaction order was obtained with respect to dideuteride coverage. The 1.5th reaction order suggests that three D atoms are involved in a single D@sub 2@ desorption, which rationalizes the third-order reaction observed in D@sub 2@ CID. Regarding ABS to form HD molecules, HD rates were determined for various @theta@@sub D@. As a result, we found that a first-order kinetics prevails the HD ABS for low D coverage regime below 0.5ML, but strangely enough, a second-order kinetics becomes dominant for high coverage regime around 1.0 ML. The second-order kinetics suggests that a direct Eley-Rideal reaction mechanism as well as hot atom mechanism are ruled out. We propose a new mechanism of hot complex mediated ABS and CID: the incident H atoms form a complex with D-Si system in the very early stages of sticking. ABS and dihydride formation occur competitively during the relaxation process of the hot complex.