Chemisorption of hydrogen on the Si(100) surface: Monohydride and dihydride phases

Abstract

We present a systematic study of the clean and chemisorbed-hydrogen-covered Si(100) surfaces. Experimentally, we used He i and He ii ultraviolet photoemission spectroscopy and were able to resolve important chemisorption features which had not been observed previously. We carried out electronic energy calculations using both empirical tight-binding and extended Hückel methods, from which we deduce a consistent interpretation of the spectra. It is found that the low-binding-energy surface states resulting from the asymmetric dimer-bond model are in good agreement with the experimental data, whereas one high-binding-energy surface state associated with the displacements of the subsurface atoms does not appear in the spectra. Hydrogen chemisorbing on the Si(100)-(2×1) surface forms a monohydride phase, and removes most of the surface states, except for the dimer bond and some of the backbonding states. Based on the theoretical and experimental results it is suggested that at high coverage the Si—H bonds of the dihydride phase rotate and depart from the tetrahedral directions. The occurrence of this phase on the other surfaces of silicon, and its possible connections with the observed spectral features, are extensively discussed.