Defects have been deliberately introduced into NiO(100) single-crystal
surfaces by Ar+ bombardment and by slow H-2 reduction, and the result
ing surfaces have been studied by changes in their Fuchs-Kliewer phono
n spectrum. Both treatments produce near-surface reduction, as measure
d by Auger electron spectroscopy. The phonon spectra are obtained by h
igh-resolution electron energy loss spectroscopy (HREELS) using 2.8 eV
electrons, with the electron loss data collected in the specular dire
ction. Sputtered surfaces show great decreases in specularly diffracte
d intensity, but result in little change in the fundamental properties
of the phonons. H-2-reduced surfaces show a more gradual decrease in
total spectral intensity but yield an equally rapid decrease in phonon
spectral intensity relative to that of the elastically scattered peak
. At large reduction values, the phonon mode shifts to lower frequency
. The changes in the phonon spectra are discussed in terms of current
understanding of the nature of the defects created in Ar+ bombardment
and in the H-2 reduction process.