Evidence for the interfacial reaction between Ni adatoms and H-Si(001) surface

Hydrogen termination of Si surfaces (H-Si) does not stop the interfacial reaction between Ni adatoms and H-Si(001) surface at room temperature. At low Ni coverage of 0.1% (equivalent to 0.02 ML), X-ray photoelectron spectroscopy (XPS) reveals a binding energy shift of Ni 2p_3/2 to 854.0 eV, which corresponds to the formation a NiSi-like environment. As the coverage of Ni increases, the Ni 2p_3/2 eventually shifts to 852.8 eV, indicative of formation of metallic Ni. XPS intensity vs Ni coverage analysis reveals a growth process akin to pseudo-layer-by-layer growth mode, thereby suggesting the formation of bulk-Si(001)/NiSi-like/Ni-rich-silicide-like/metallic Ni structure as growth proceeds. For Ni coverage not more that 33% (equivalent to 12.68 ML), Ni remains protected by the silicide environment and no oxidation of Ni to form Ni-oxides was observed even after exposing the samples to air for 400 days. For samples with Ni coverage above 41%, oxidation of Ni is observed by presence of NiO and NiSiO₃ peaks at 854.5 and 857.0 eV, respectively. The current studies suggest that there is reaction between Ni adatoms and Si at the growth front on H-Si(001) surfaces upon Ni deposition at room temperature and hydrogen termination does not suppress the interface reaction between Ni and Si.