Characterization of evaporated germanium films by inelastic electron tunneling spectroscopy

Vibrational spectra of thin (∼ 1 nm) films of evaporated germanium on alumina surfaces have been measured by inelastic electron tunneling spectroscopy. The tunneling spectra of the evaporated Ge films were compared with the vibrational spectra of surface species on crystalline Ge formed from reactions with atomic hydrogen, water, and oxygen measured by high-resolution electron energy loss spectroscopy and multiple internal reflection infrared spectroscopy and they showed the formation of germanium hydride species. Monohydride is predominantly formed in films prepared both in high vacuum (10 −6 Torr) and in an atmosphere of H 2O (10 −5 Torr). The tunneling spectra of the heated (125–150°C) Ge films showed that the monohydride is stable in this temperature range. The vibrational frequencies for the hydride species in the films compare more closely to those for crystalline Ge surfaces than to those for amorphous Ge. The hydride is formed from the reaction with residual water molecules in the vacuum system during the evaporation and is considered to be present mainly on the surfaces and grain boundaries of the films to terminate the dangling bonds.