CHARACTERIZATION OF EVAPORATED SI AND SIO FILMS BY INELASTIC ELECTRON-TUNNELING SPECTROSCOPY

Vibrational spectra of thin (1-2nm) films of evaporated silicon and silicon monoxide on alumina surfaces have been measured by inelastic electron tunneling spectroscopy. Analysis of the tunneling spectra of the Si and SiO films and comparison with the vibrational spectra of surface species on crystalline Si formed from reactions with hydrogen atoms, water, and oxygen measured by high-resolution electron energy loss spectroscopy and multiple internal reflection infrared spectroscopy showed the formation of silicon hydride species. Monohydride is predominantly formed in Si films prepared in high vaccum (10(-6) Torr), whereas dihydride and trihydride are formed in an atmosphere of H2O (10(-5) Torr). Monohydride is preferentially formed in SiO films prepared both in high vacuum and in an atmosphere of H2O. These hydrides are stable against H2O, CH3OH, and NH3 due to the strong covalent character of the Si-H bonds. The tunneling spectra of the Si films evaporated on heated (150-283-degrees-C) alumina surfaces showed that the monohydride is stable, while the dihydride and trihydride are unstable at high temperatures. The tunneling spectra of the SiO films evaporated at 283-degrees-C in an atmosphere of H2O compare closely to those of the corresponding Si films, suggesting a similar structure for these evaporated films. The hydrides are formed from the reaction with residual water molecules in the vacuum system during the evaporation and are considered to be present mainly on the surfaces and grain boundaries of the films to terminate the dangling bonds.