ELECTRON-ENERGY-LOSS CHARACTERIZATION OF THE H-TERMINATED SI(111) AND SI(100) SURFACES OBTAINED BY ETCHING IN NH4F

Specular high-resolution electron-energy-loss spectroscopy studies of Si(111) and Si(100) surfaces etched in 40% ammonium fluoride solutions confirm that the silicon surfaces are completely terminated with hydrogen, with no detectable impurities such as oxygen, fluorine or hydrocarbons. All the observed loss peaks are dominated by impact scattering and can be assigned to silicon-hydrogen vibrations and to silicon phonons. For the atomically flat, ideally H-terminated Si(111) only, referred to as the H/Si(111)-(1 X 1), a new loss peak is observed at 795 cm-1, which cannot be assigned to impurities or defects. We present arguments suggesting that this peak may be a manifestation of a strong anharmonic coupling between the two-phonon band of a silicon phonon at almost-equal-to 330 cm-1 and the Si-H bending vibration (at almost-equal-to 650 cm-1).