IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS3-TuP

Paper SS3-TuP26
Adsorption and Absorption of Hydrogen by Ti(0001): A Study Combining Surface Characterization and Non-destructive H-Depth Profiling

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Adsorption/Desorption Poster Session
Presenter: M. Wilde, University of Tokyo, Japan
Authors: M. Wilde, University of Tokyo, Japan
M. Matsumoto, University of Tokyo, Japan
K. Fukutani, University of Tokyo, Japan
T. Okano, University of Tokyo, Japan
Y. Mizuno, Chiba Institute of Technology, Japan
T. Homma, Chiba Institute of Technology, Japan
Correspondent: Click to Email
In the present work the interaction of the Ti(0001) single crystal surface with molecular H@sub 2@ and atomic H is studied at temperatures of 100-300 K. We combine standard UHV techniques of clean surface preparation and characterization with hydrogen depth-profiling by nuclear reaction analysis (NRA, via the @sup 1@H(@sup 15@N,@alpha@@gamma@)@sup 12@C reaction), which allows straightforward assigning of the features in H@sub 2@ thermal desorption spectra (TDS). Molecular H@sub 2@ admitted at T<120 K gives rise to three desorption features in TDS at 160 K, 240 K and 320 K. Absorption of hydrogen by the single crystal surface is only observed after exposure to atomic H. NRA depth profiles indicate that the amount and depth distribution of absorbed H atoms is strongly dependent on the exposure temperature T@sub e@. Below 240 K, the uptake of atomic H saturates and thin (@<=@5 nm) hydrogen-rich overlayers are formed that contain up to a few ML of H atoms and passivate the metal against further H absorption. This near-surface H accumulation results from the efficient surface penetration by H-atoms and the restricted diffusional transport of H in the metal at the given T@sub e@. Above 240 K facile diffusion readily distributes the absorbed H into the Ti bulk. Despite rather different H-depth distributions after H absorption between 100 K and 300 K, only a single H@sub 2@ desorption peak at 480-500 K is observed in TDS in all cases. An ultra-thin oxide overlayer on Ti(0001) is found to completely de-activate the surface against hydrogen sorption, whereas the outgassing of H traces dissolved in the deeper metal bulk occurring at T>650 K is unaffected. The outgassing rate is characterized by an activation energy in excellent agreement with the heat of H solution in @alpha@-Ti of 21.6 kcal/mole.