TY - JOUR
T1 - Hydrogen absorption in epitaxial W/Nb(0 0 1) and polycrystalline Fe/Nb(1 1 0) multilayers studied in situ by X-ray/neutron scattering techniques and X-ray absorption spectroscopy
AU - Klose, F.
AU - Rehm, Ch
AU - Fieber-Erdmann, M.
AU - Holub-Krappe, E.
AU - Bleif, H. J.
AU - Sowers, H.
AU - Goyette, R.
AU - Tröger, L.
AU - Maletta, H.
PY - 2000/6
Y1 - 2000/6
N2 - Hydrogen can be absorbed in large quantities by 100 angstroms thin Nb layers embedded in epitaxial W/Nb and polycrystalline Fe/Nb multilayers. The solubility and the hydrogen-induced structural changes of the host lattice are explored in situ by small-angle neutron/X-ray reflectometry and high-angle diffraction. These measurements reveal for both systems that the relative out-of-plane expansion of the Nb layers is considerably larger than the relative increase of the Nb interplanar spacing indicating two distinctly different mechanisms of hydrogen absorption. In Fe/Nb multilayers, hydrogen expands the Nb interplanar spacing in a continuous way as function of the external pressure. In contrast, the Nb lattice expansion is discontinuous in epitaxial W/Nb multilayers: A jump in the Nb(0 0 2) Bragg reflection position occurs at a critical hydrogen pressure of 1 mbar. In situ EXAFS spectroscopy also exhibits an irreversible expansion of the Nb lattice in the film plane for pH(2)>1 mbar. This can be regarded as a structural phase transition from an exclusively out-of-plane to a three-dimensionally expanded state at low and high hydrogen pressures, respectively.
AB - Hydrogen can be absorbed in large quantities by 100 angstroms thin Nb layers embedded in epitaxial W/Nb and polycrystalline Fe/Nb multilayers. The solubility and the hydrogen-induced structural changes of the host lattice are explored in situ by small-angle neutron/X-ray reflectometry and high-angle diffraction. These measurements reveal for both systems that the relative out-of-plane expansion of the Nb layers is considerably larger than the relative increase of the Nb interplanar spacing indicating two distinctly different mechanisms of hydrogen absorption. In Fe/Nb multilayers, hydrogen expands the Nb interplanar spacing in a continuous way as function of the external pressure. In contrast, the Nb lattice expansion is discontinuous in epitaxial W/Nb multilayers: A jump in the Nb(0 0 2) Bragg reflection position occurs at a critical hydrogen pressure of 1 mbar. In situ EXAFS spectroscopy also exhibits an irreversible expansion of the Nb lattice in the film plane for pH(2)>1 mbar. This can be regarded as a structural phase transition from an exclusively out-of-plane to a three-dimensionally expanded state at low and high hydrogen pressures, respectively.
UR - http://www.scopus.com/inward/record.url?scp=0033733189&partnerID=8YFLogxK
U2 - 10.1016/S0921-4526(99)01933-X
DO - 10.1016/S0921-4526(99)01933-X
M3 - Conference article
AN - SCOPUS:0033733189
SN - 0921-4526
VL - 283
SP - 184
EP - 188
JO - Physica B: Physics of Condensed Matter
JF - Physica B: Physics of Condensed Matter
IS - 1-3
T2 - 6th International Conference on Surface X-ray and Neutron Scattering (SXNS-6)
Y2 - 12 September 1999 through 17 September 1999
ER -