Here we propose to use the superior energy resolution of OSIRIS to measure the phonon desnity of states (PDOS) of both nanocomposite and bulk thermoelectric alloys of Si1-xGex. Previous results have shown that upon entering the nanocrystalline regime these systems manifest large increases in their thermoelectric figures of merit (ZT) stemming from a substantial reduction in their thermal conductivity. To date, however, little is understood regarding the precise nature of the interfacial scattering and resulting modifications to the PDOS in these materials. Here we propose to probe the long wavelength phonon modes in Si1-xGex nanocomposites with the superior energy resolution achievable on the OSIRIS spectrometer.