(Invited) Particle Size-Dependent Photoelectron Plasmon Loss Features in Deposited Germanium Nanocrystals

The plasmon loss features of deposited and well-characterized germanium nanocrystals with average sizes of 3.5 and 4.5~nm, respectively, are investigated with photoelectron spectroscopy at the Ge~3d core level. We observe a particle size dependence of the surface plasmon amplitude with respect to the bulk plasmon consistent with the changing surface-to-bulk atom ratio. Additionally, the nanocrystal surface plasmons are redshifted with respect to a bulk reference by up to 0.4~eV for 3.5~nm particles. For the bulk plasmons no significant size dependent energy shifts can be observed for nanoparticle sizes down to 3.5~nm.