AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM8
Kinetics of H Atom Adsorption on Si(100) at 325 - 600 K

Monday, November 3, 2003, 10:40 am, Room 326

Session: Gas-Surface Dynamics
Presenter: A. Kutana, University of Houston
Authors: A. Kutana, University of Houston
B. Makarenko, University of Houston
I.L. Bolotin, University of Houston
J.W. Rabalais, University of Houston
Correspondent: Click to Email
The kinetics of atomic hydrogen isothermal adsorption on a Si(100) surface has been studied by the time-of-flight scattering and recoiling spectrometry (TOF-SARS) technique. A continuous decrease in saturation coverage with temperature under constant atomic hydrogen exposure has been observed for temperatures in the range 325 - 650 K. It is suggested that the obtained coverages are a result of a kinetic equilibrium between competing adsorption, abstraction, and migration reactions occurring at the surface. This approach explains how the coverages corresponding to the well-known phases of hydrogen on Si(100) at different temperatures are obtained. Introducing two types of adsorption sites into the model for the Si sticking probability, the coverage decrease is shown to be due to depletion of the surface concentration of atoms in the secondary adsorption sites. For lower temperatures, there is a significant concentration of hydrogen atoms in the precursor states that saturate the monohydride dangling bonds after hydrogen source shut-off and discontinuation of Eley-Rideal abstraction. The time for this transition is on the order of @kappa@(1 - n@sub sat@), where n@sub sat@ is the saturation coverage for a given temperature. Increasing the temperature leads to an increase in the migration rate from secondary to primary sites, where more efficient Eley-Rideal abstraction causes a decrease in total concentration. The migration constant @kappa@ obeys the Arrhenius equation with a low activation energy of 0.29 eV. It follows from the model, and has been proven experimentally, that the saturation coverage depends not only on temperature, but also on the incoming hydrogen flux, i.e. the ambient H@sub 2@ pressure at which adsorption is performed.