Abstraction and desorption kinetics in the reaction of H+D/Si(100) and the relation to surface structure

Abstract

Kinetics of HD and D2 desorption from D/Si(100)-2×1 surfaces induced by H atoms has been investigated at temperature range of 97–685 K. Desorption rates of HD and D2 are measured in real-time by using mass spectrometers during the exposure of D/Si(100) to H atom beam. HD and D2 rates are not fitted by a hot atom kinetics, but are explained well in terms of adjacent double di-hydrides (DDI)-thermal desorption plus abstraction mechanism. For Ts⩾480 K, the pre-adsorbed D atoms are desorbed as D2 via DDI-desorption (∼22%), as HD via DDI-desorption (∼28%), and HD via abstraction (∼50%). For Ts⩽310 K, DDI-desorption does not occur, whereas the abstraction proceeds at a constant rate. The yield of DDI-desorption decreases as the surface structure of H/Si(100) changes from 2×1 to 1×1, suggesting the DDI-desorption is associated with a re-formation reaction of a mono-hydride dimer from adjacent two di-hydrides. The activation energy (Ea) for DDI-desorption is ∼0.2 eV. The rate of abstraction does not show Arrhenius-type temperature dependence. The abstraction probability PHD is estimated at 0.03±0.015 (cross section σHD=0.4±0.2 Å2) for Ts⩽310 K.