Surface and interface effects on plasmon loss features in Ge thin films and Si/Ge multilayers

The influence of surface and interface structures on plasmon loss features of Ge thin films and Si/Ge multilayer structures (MLS) has been studied using synchrotron radiation based photoemission spectroscopy. The core level plasmons that occur in the neighbourhood of the Ge-3d core level (17.35 eV) in thin film Ge are shifted by 0.43 eV, while those in Si/Ge MLS (17.52 eV) are shifted by 0.6 eV as compared to the position in bulk Ge. These shifts indicate formation of nanostructures in both cases. The probable reasons for the change in the plasmon energy are the quantum confinement effect in thin film Ge, while in the case of Si/Ge MLS, intermixing and roughness at the interfaces seem to play a dominating role affecting the overall electronic properties. These results are supported by structural characterization using Raman spectroscopy.