Adsorption and reaction of HfCl4 with H2O-Terminated si(100)-2 x 1

A combined experimental and density functional theory study has been performed to investigate the bonding arrangements, saturation coverage, and factors that limit the saturation coverage for the adsorption of HfCl4- (g) on a water-terminated .Si(100)-2 x 1 surface. Experiments with X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and reflection high-energy electron diffraction show that adsorption occurs at hydroxyl sites and forms an atomically abrupt metal-oxide/semiconduct'or interface. The saturation Hf coverage is measured at (2.0 +/- 0.2) x 10(14)/cm(2), which is approximately 2/3 of the available hydroxyl sites. Density functional theory calculations of various configurations of adsorbed OHfCl3 fragments show a strong interaction between the adsorbed fragment and neighboring hydroxyls. On the basis of the density functional theory calculations, a random adsorption model has been constructed to model the adsorption of H-2,O(g,) on Si(100)-2 x 1 and the adsorption of HfCl4(g) on the H2O-Si(100)-2 x 1 surface. The model predicts a saturation coverage of (2.05 +/- 0.05) X 10(14) Hf/cm(2), which is close to the experimental data. The main factor that limits the reactant coverage is found to be a preferred reaction at two hydroxyl sites. The surface. is made up of roughly equal numbers of OHfCl3 and (O)(2)HfCl2 adsorbates. The extension of the results to adsorption and reaction on SiO2 is discussed.