Chemisorption Energetics of Superactive Chlorine Containing Species on Gallium Arsenide Surfaces

The chemisorption mechanisms of Cl2, Br2, and I2 on Si(100) 2xl are quite similar while those of F2 and O2 are quite distinct. For the heavy diatomic halogens (Cl2, Br2, and Cl2), the sticking probability increases with incident translation energies above 0.1 eV, and the largest initial sticking probabilities are obtained at the highest incident energies, with S subO, equal to 95 - 100% for I2 and Br2, at low incident energies the initial sticking probability, SO, decreases with increasing surface temperature while at high incident energies the sticking probability is independent of surface temperature. In addition, for Cl2 very low energy molecular beams can be prepared, and the sticking probability is observed to decrease with increasing incident energies between 0.02 eV and 0.06 eV. Therefore, all these heavy diatomic halogens can adsorb via precursor - mediated chemisorption at low incident translation energy and via direct - activated chemisorption activated chemisorption at high incident translational energy. For all incident kinetic energies, the chemisorption probability decreases linearly with coverage (S=S0(1-Theta) for the three diatomic halogen gases. This suggests that a single site is required to initiate the direct chemisorption process and the precursor is intrinsic.