Preparation and characterization of clean, single-crystalline YHx films (0 <= x <= 2.9) on W(110)

Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We report on the preparation of clean, single-crystalline YHx films (0⩽x⩽2.9). The films have been characterized in situ combining angle-resolved photoelectron spectroscopy (ARPES) and low energy electron diffraction. Direct Y dihydride growth, i.e., Y evaporation under a H2 partial pressures of ≈5×10−6 mbar at 500 K on W(110), is the most convenient starting point for the preparation of clean single-crystalline Y hydride films covering H concentrations from the “clean metal” (x≈0) up to the lower boundary of the pure trihydride phase (x≈2.9). Upon annealing Y dihydride films the desired H concentration can be adjusted within the α-phase or the (α+β) two-phase regime. On the other hand, the extension of our photoelectron spectrometer with an homemade ultrahigh vacuum (UHV) compatible hydrogenation system allows to induce the transition from Y dihydride to Y trihydride withi...