Tetragonal germanium flims deposited by the cluster-beam evaporation technique

Abstract

Germanium (Ge) films have been fabricated by the cluster-beam technique. In transmission electron microscope (TEM) micrographs, the film deposited on a substrate at room temperature appears smooth and uniform, while that deposited at liquid nitrogen temperature consists of nanostructures with diameters from 4 to 40 nm. The x-ray diffraction (XRD) patterns show that the crystalline structure for either deposition temperature is not the ordinary diamond structure but is tetragonal. The absorption spectra are distinct from that of bulk Ge. The photo-oxidized Ge nanostructures exhibit blue light emission, which is strong enough to be recognized with the naked eye even under a room light.