Effects of high temperature and e-beam irradiation on the stability of refractory thin films

Refractory thin films of Al2O3, ZrO2, MgO, ThO2, and BN have been investigated in situ in an UHV transmission electron microscope. The electron transparent refractory films were prepared by e-beam evaporation, anodization, rf sputtering, and thinning of bulk crystal materials. The study concentrates on monitoring the thermal and mechanical stability of the films, phase and structural changes, and electron irradiation effects as a function of film-preparation conditions. With increasing temperatures, five different crystallographic phases were observed for both anodized and e-beam-evaporated alumina films. Zirconia films exhibited two phase transitions upon heating to 1200degreeC and electron-irradiation-induced crystallization of ZrO2 even at room temperature. MgO, ThO2, and BN films did not undergo any noticeable phase transformation but ruptured due to sintering below 1200degreeC. In general it was found that crystalline forms of thin films exhibited higher thermal and radiation stability than amorphous films. The results show that the radiation damage is mainly due to beam-induced dissociation and is enhanced in nonstoichiometric materials