Hydrogen Termination of the NH 4 F-Treated Si(111) Surface Studied by Photoemission and Surface Infrared Spectroscopy

The Si(111) surface treated in NH4F has been investigated using photoemission and surface infrared spectroscopy (SIS). We confirm both with photoemission and SIS measurements that the NH4F-treated Si(111) surface is dominantly terminated with the monohydride Si (Si-H) oriented perpendicular to the surface and is free from silicon oxide. Photoemission and SIS data also demonstrate that ammonium fluorides react with the Si substrate to generate the hexafluorosilicate salt, (NH4)2SiF6. We propose that the formation of (NH4)2SiF6 or SiF6 2− ions plays an important role in the NH4F etching of Si crystals.