We report measurements of infrared (ir) vibrational absorption made on thin films of rf-sputtered $a$-Si: H bombarded with 100- and 200-keV ${\mathrm{He}}^{+}$ ions, and also after an anneal at temperatures up to 320 °C. We find that the integrated intensities of ir vibrational bands at 2000 and 850 ${\mathrm{cm}}^{-1\mathrm{}}$ are enhanced significantly after the bombardment, whereas bands at 2100, 890, and 650 ${\mathrm{cm}}^{-1\mathrm{}}$ show little change. Annealing at 320 °C reduces the integrated intensities of the 2000- and 850-${\mathrm{cm}}^{-1\mathrm{}}$ peaks, again with little change in the other peaks, thus reversing the effect of bombardment. We explain these observations in terms of changes in the oscillator strengths of the vibrational modes induced by defects created near the vibrating complex during bombardment. The significance of the dependence of the ir oscillator strengths on the local defect structure and its implications for the interpretations of ir spectra are discussed.

• Received 15 January 1980

DOI:https://doi.org/10.1103/PhysRevB.22.880