Phonon Dispersion of Diamond Measured by Inelastic X-Ray Scattering

Abstract

We report on a study of phonons in diamond using a new instrument for high resolution inelastic x-ray scattering at the Advanced Photon Source. We have paid particular attention to possible overbending of the most energetic branches, i.e., LO along both $\Gamma -X$ ( $\equiv \Delta$) and $\Gamma -L$ ( $\equiv \Lambda$) and the elliptically polarized ${\Sigma }_3$ branch along $\Gamma -K$ ( $\equiv \Sigma$). Overbending along all three directions has been invoked in recent years to explain a famous and extraordinary peak in the two-phonon Raman spectrum. Our data reveal overbending only along $\Delta$.