Observation of Phase Transitions in Hydrogenated Y Films Via IR Emissivity Imaging
Jason Hattrick-Simpers, Ke Wang, Raymond Cao, Chun Chiu, Edwin J. Heilweil, Robert G. Downing, Leonid A. Bendersky
Direct observation of a sequence of phase transitions during hydrogenation of Y thin films has been realized through the use of in-situ isothermal IR emissivity measurements. The formation of different phases, α-Y(H), YH2 and YH3, has been identified based on observation of the changes in the slope of the IR emissivity vs. time curve during the hydrogen loading experiments. The presence of the appropriate phases was confirmed by ex-situ x-ray diffraction and Prompt Gamma Activation Analysis (PGAA). Transmission electron microscopy (TEM) demonstrated single crystal orientation relationships between the Al2O3 substrate, Ti buffer layer, the as-deposited Y film, as well as its hydrides. These results clearly demonstrate the power of IR emissivity imaging to monitor, in real time, the formation of hydride phases of both metallic and insulating character near the surface of a thin-film sample.