Final evidence for H termination of HF-treated Si surfaces: a comparative study by high-energy and vibrational spectroscopies

The aim of this article is to provide a comparative analysis of Si(100) surfaces after etching in HF in order to attain final conclusions concerning the chemical termination of the surface. We report a comparative study of the Si surface chemistry carried our simultaneously using both vibrational and high-energy techniques. While vibrational spectroscopies (high-resolution electron energy loss spectroscopy as well as multiple internal reflection infrared spectroscopy) show no evidence of the presence of Si-F bonds, Auger spectroscopy provides clues on the presence of small amounts of F at the surface. Such apparently contradictory results have, in the past, raised doubts about the actual way surface bonds are saturated. It will be shown that fluoride ions are actually present on the Si surfaces as ionosorbed species, while Si bonds are exclusively saturated by H atoms. We will further confirm how the Si(100) surface chemically etched in diluted HF is terminated not only by SiH2 groups, but also by mono- and trihydrides as a result of the nano-roughening induced by the etching processing. Low-energy electron diffraction analyse confirm and corroborate these conclusions, as they show diffraction maps from highly disordered (2 x 1) reconstructed surfaces.