Raman scattering and surface disorder in amorphous germanium

We report here on in situ enhanced Raman scattering performed on a-Ge films prepared in ultra high vacuum. The results demonstrate the capability of studying the vibrational states of amorphous solids below an equivalent thickness of one monolayer. The Raman spectra are found to exhibit changes in spectral form with film thickness over the entire spectral region. These variations are substantial, demonstrating increased structural disorder in a-Ge as thickness decreases due to near surface disorder.