Low-temperature and low-H2 pressure synthesis of hydride semiconductor YH3 −δusing Pd/Ni co-capped Y films

With an aim of decreasing the temperature (Tγ) at which metallic Y reacts with H2 to form the semiconductor phase YH3−δ, we employed Pd and Ni co-capping layers as catalysts, and compared the result with those obtained when employing Pd or Ni single-capping layers. These Y films capped with three types of catalytic layers were deposited by electron beam evaporation, and subsequently hydrogenated at a H2 partial pressure of approximately 3×103 Pa while varying the H2 reaction temperature (TH2) from 20° C to 500° C. Pd/Ni co-capping materials exhibited a Tγ of ≃ 50° C, which is approximately 40° C lower than that of Ni capped materials. With regard to Pd-capped material, the metal-dihydride phase YH2±δ prevailed for all investigated TH2. Quantitative studies in terms of the Gibbs free energy were conducted by assessing the molar concentrations of the YHδ<0.21, YH2±δ, and YH3−δ phases from corresponding X-ray diffraction intensities.