CHARACTERIZATION OF EVAPORATED SILICON FILMS BY INELASTIC ELECTRON-TUNNELING SPECTROSCOPY

Vibrational spectra of thin (1-2 nm) films of evaporated silicon on alumina surfaces have been measured by inelastic electron tunneling spectroscopy. Analysis of the tunneling spectra of the evaporated Si 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 films prepared in high vacuum (10(-6) Torr), whereas dihydride and trihydride are formed in films prepared in an atmosphere of H2O (10(-5) Torr). These hydrides are formed from the reaction with residual water molecules in the vacuum system during the evaporation. 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 vibrational frequencies for the hydride species in the films compare more closely to those for crystalline Si surfaces than to those for amorphous Si, suggesting a microcrystalline structure for the evaporated Si films.