A comprehensive study of electron energy losses in Ge nanowires

We present a comprehensive study of electron energy losses by fast electrons that occur in isolated single-crystal Ge nanowires with organic monolayer-passivated surfaces. A similar to0.5 nm diameter electron probe in a scanning transmission electron microscope equipped with an energy loss spectrometer (STEM-ELS) was used to study plasmon and core electron excitations. Losses due to scattering from volume and surface plasmons vary with respect to the probe position relative to the nanowire surface, and the volume plasmon energy increases with decreasing diameter for nanowires narrower than 24 nm. Below 24 nm, the organic monolayer-coated nanowires also exhibit size-dependent Ge 3d core ionization spectra that shift to higher energy with reduced diameter that are independent of probe position relative to the surface. In contrast, the Ge 3d edge for surface-oxidized nanowires exhibits a chemically induced shift when positioned near the surface.