OBSERVATION OF THE REVERSIBLE H-INDUCED STRUCTURAL TRANSITION IN THINY-FILMS VIA X-RAY PHOTOELECTRON DIFFRACTION

Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We rep ort on the reversibility of hydrogen loading in thin single-crystallin e Y films grown by vapor deposition on W(110). Under a H-2 partial pre ssure of 1x10(-5) mbar the hexagonal-closed-packed Y films convert to the face-centered-cubic Y dihydride. Unloading is accomplished by anne aling the dihydride to 1000 K. No loss of crystallinity is observed du ring these martensitic transformations of the Y lattice. Moreover, we demonstrate a model to determine the H concentration in Y in situ.