Ab-initio Energy Loss Spectra of Si and Ge Nanowires

We report an ab initio investigation of the energy-loss probability of fast electrons in silicon and germanium nanowires. Computed energy loss spectra are characterized by a strong enhancement of the direct interband transitions peak at low energy, in good agreement with experimental data. Our calculations predict an important diameter dependence of the bulk volume plasmon peak for very thin wires which is consistent with the blue shift observed experimentally in thicker wires.