Structural evolution and thermal stability of deuterated titanium thin films

The thermal stability and structural evolution of titanium thin films deposited in a deuterium atmosphere were studied by x-ray diffraction (XRD), thermal-desorption spectroscopy (TDS), and differential scanning calorimetry. Samples deposited at a 423-K substrate temperature present the fcc CaF₂-like structure of δ-TiD₂. TDS experiments showed that deuterium thermal desorption follows a first-order kinetic characterized by a free activation energy of 1.63±0.03eV. When samples made of the fcc phase were submitted to thermal annealing at 723 K, XRD measurements revealed a crystalline transformation to the hcp {α}-Ti structure. These results indicate that the titanium deuteride decomposition is the rate-limiting process in deuterium desorption. Films deposited at 573- and 723-K substrate temperatures are made of deuterated {α}-Ti: for these samples deuterium desorption followed a second-order kinetics with a free activation energy of 1.53±0.02eV, and the rate-limiting process was the surface recombinative desorption of D atoms.