Ultraviolet photoelectron spectroscopy of semiconductor clusters: Silicon and germanium

Abstract Ultraviolet photoelectron spectra (UPS) are reported here for semiconductor clusters prepared in a supersonic beam. Using a new magnetically focused time-of-flight photoelectron spectrometer, UPS spectra were obtained for mass-selected negative cluster ions of silicon and germanium in the 3-12-atom size range. An ArF excimer laser (6.4 eV) was used for photodetachment, enabling the first 3–4 eV of the valence band structure of the clusters to be probed. With few exceptions, the UPS data for corresponding clusters of the two semiconductors were remarkably similar. The spectra suggest that clusters 4, 6, 7, and 10 of silicon and 4, 6 and 7 of germanium are closed-shell species with band gaps of 1 to 1.5 eV.