Abstract
Samarium films capped with a thin palladium overlayer undergo a metal to semiconductor transition during in-situ hydrogen loading (PH2=1.01×105 Pa) at room temperature. The transition is accompanied by a change in optical appearance, i.e. metallic gray samarium films change to golden greenish transparent samarium hydride (SmH3-δ) films. Glancing angle X-ray diffraction (GAXRD) studies show that the rhombohedral structure of metallic samarium films changes to hexagonal structure of the SmH3-δ films with average lattice parameters of a=3.775 Å, c=6.743 Å. A direct optical band gap of 3.0 eV has been obtained for SmH3-δ films from reflectance and transmittance data. The Hall coefficient measured as a function of hydrogen concentration, changes from a metal-like RH value -14.9×10-10 m3/C to -1081.8×10-10 m3/C for SmH3-δ films. On unloading hydrogen, the value of RH changes to -3.85×10-10m3/C at the dihydride composition.