Complexity of H-bonding between polar molecules on Si(100)-2 × 1 and Ge(100)-2 × 1 surfaces

The adsorption of various combinations of three polar molecules (NH 3 , H 2 O, and HF) on Si/Ge(100) surface is studied by first-principles calculations. On a given pre-adsorbed substrate, the H-bonding and dative bonding always show a synergistic effect, together with the electrostatic attraction, dominating the adsorption and dissociation of polar molecules on Si/Ge(100). Both H 2 O and HF are found to be energetically favored to cluster with the pre-adsorbed H 2 O molecule on Si/Ge(100) surface. Catalyzed by H 2 O, the dissociation barriers of H 2 O on Ge(100) decrease from ~ 0.7 to ~ 0.4 eV, in comparison with the nearly an order of magnitude reduction on Si(100). Furthermore, H 2 O molecule dissociates spontaneously on Si(100) and the barriers are lowered to ~ 0.2 eV on Ge(100) when catalyzed by HF, providing an efficient approach for dissociation of H 2 O on Si(100) and Ge(100) surfaces.