Structural properties of Ge nanocrystals synthesized by a PVD nanocluster source

In this study, the synthesis of Ge nanoparticles by a physical vapour deposition (PVD) nanocluster source has been investigated. We typically obtain Ge nanoparticles with a mean diameter between 4 and 9 nm. The microstructure of Ge nanoparticles was widely studied by high resolution transmission electron microscopy, energy filtered transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The main result is the capability of the PVD process to synthesize well crystallized Ge nanocrystals at room temperature and without any post thermal annealing. It was found from Raman analysis that these room temperature deposited nanoparticles are composed of a Ge crystalline core and a sub-nm thick amorphous Ge shell. A low temperature annealing (450 °C) during 1 h under vacuum leads to the reorganization of the surface atoms while longer annealing seems to promote the formation of a Ge oxide shell around the nanoparticles.