ELECTRON-ENERGY LOSS SPECTROSCOPY OF H-TERMINATED SI(111) AND SI(100) PREPARED BY CHEMICAL ETCHING

H-passivated Si(111) and Si(100) surfaces, prepared by chemical etching in a 40% ammonium fluoride solution, are investigated with high resolution electron energy loss spectroscopy. Extensive off-specular and energy dependence studies reveal that the scattering process is not dipolar, as previously thought, but rather is dominated by short-range interactions. On the atomically flat H/Si (111)-(1 X 1) surface, two new substrate phonons are observed in addition to the Si-H stretch (2084 cm-1), the Si-H bend (636 cm-1), and the 520-cm-1 substrate mode: a loss at 390 cm-1 assigned to a bulk phonon transition and a loss at 110 cm-1 assigned to a surface phonon resonance.