Direct observation of a multiple-peak structure in the Raman spectra of Ge-74 and Ge-70 nanocrystals

Raman scattering (RS) spectra were measured in samples of germanium nanocrystals (Ge-NC) prepared by ion-implantation of Ge-74 and Ge-70 isotopes into an amorphous SiO2 layer initially grown on a Si < 100 > surface. A rich multiple-peak structure has been detected in addition to the well-known Ge-Ge peak at about 300 cm(-1) of bulk Ge. Specifically, new Ge-74-NC-related peaks centered around 202 cm(-1), 217 cm(-1), and 317 cm(-1) were directly observed as verified by isotopic Raman shift in Ge-70-NC samples. Lorentzian line shape fit of the RS spectra implies the existence of two additional Ge-related vibration modes around 260 cm(-1) and 360 cm(-1). The origin of each of the Ge related peaks was determined using a theoretical calculation based on the harmonic approximation. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789802]