Residual gap surface states along variously hydrogenated silicon (111) and (100) surfaces

Different H-saturated silicon surfaces have been studied by low-energy electron diffraction and photoemission yield spectroscopy, Hydrogenation was performed in ultrahigh vacuum (UHV) with an atomic H flux upon a Si(100)-(2 x 1) surface either at room temperature or at 350 degrees C, and upon cleaved (2 x 1) or (7 x 7) Si(111) surfaces. H-saturated Si(111) was also achieved via a chemical treatment prior its introduction into UHV. Analysis of the PYS curves shows that these surfaces both show scattering effects and contain residual surface-state densities in the gap which strongly depend on the surface and on the hydrogenation procedure. The chemically hydrogenated Si(111) surfaces are the smoothest at the atomic scale, as proved by the lowest gap state density and the least surface scattering effects.