Low frequency coherent Raman scattering of spherical acoustical vibrations of three-dimensional self-organized germanium nanocrystals

The Ge+SiO2 and SiO2 alternating multilayers are prepared by the magnetron sputtering of germanium and silica targets. By controlling the substrate temperature and by subsequent thermal annealing, the self-organized germanium quantum dots in 3D rombohedral (R 3 m) superlattice are produced. The polarized low-frequency Raman scattering measurements shows the coherent effects on the symmetric and quadrupolar spheroidal vibrations of Ge nanocrystals. It has been shown that the coherence effects are dependent on degree of Ge-ordering in the superlattice.