Abstract
Nuclear resonant inelastic x-ray scattering of synchrotron radiation was used to measure directly the partial vibrational density of states (VDOS), , of crystalline and amorphous thin films prepared by codeposition in ultrahigh vacuum. The structure of the samples was characterized by x-ray diffraction and Mössbauer spectroscopy. The VDOS of extends up to and exhibits a strong peak at and weaker bands centered at about 25, 43, and . These characteristic features coincide with positions of prominent IR and Raman spectral lines reported in the literature. The measured VDOS shows good agremeent with the theoretical VDOS of crystalline computed by using the density functional theory combined with the direct method. Contrary to the crystalline phase, the VDOS of shows a broad peak at with little structure, and a deviation from Debye behavior at small excitation energies . This is revealed as a peak in the reduced VDOS, , at , which is interpreted as “boson peak.” Above the boson peak was observed to be approximately , with being close to .
2 More- Received 7 August 2004
DOI:https://doi.org/10.1103/PhysRevB.71.035309
©2005 American Physical Society