VIBRATIONAL PROPERTIES OF H/SI(111)-(1X1) SURFACES - INFRARED-ABSORPTION AND ELECTRON-ENERGY LOSS SPECTROSCOPIC STUDIES

Flat, ideally H-terminated Si(111) surfaces can be chemically prepared with different degrees of homogeneity. The chemical and structural perfection of these surfaces has been investigated with infrared absorption and electron energy loss spectroscopies. The infrared lineshape of the Si-H stretch is clearly dependent on the extent of the perfect domains, and can be used as a probe of the structural perfection of the H/Si(111)-(1 X 1) surfaces. Best prepared surfaces contain domains, with an average size of 2 X 10(4) Si-H units. The samples contain no contaminant, at least to a 1% level, as inferred by electron energy loss spectra. The electron scattering mechanism is dominated by impact scattering, except for an intriguing loss, located at 795 cm-1. Chemical origin of this mode is discussed, but does not appear to be well supported. A strong anharmonic coupling (or Fermi resonance) between a silicon surface phonon and the Si-H bending mode is invoked.