XANES study of hydrogen incorporation in a Pd-capped Nb thin film
Abstract
X-ray absorption near-edge structure (XANES) measurements were used to probe the H-charging-induced electronic structure changes of a 2400 Å Nb film capped with Pd. These results are discussed in terms of ab initio linear augmented plane-wave (LAPW) band-structure calculations for this material. The Pd-L3-edge XANES clearly manifested the spectral (Pd-d state related) changes expected for Pd-hydride formation, a white line feature degradation, and the appearance of a Pd-H antibonding feature at 6 eV above the threshold. The Nb-L2,3 edge changes with H charging show a distinct enhancement of the white line strength; a feature 6 eV above the edges, associated with Nb-H antibonding states in analogy with the Pd results; the suppression of a threshold-onset feature of Nb metal; and a shift of the centrum of the white line feature towards the threshold. Comparison of the Nb sphere projection of the d3/2 component of the LAPW density of states (DOS) to the Nb-L2-edge spectra yields good basic agreement with the observed spectral changes. In particular, the substantial theoretical reduction in the DOS at, and just above, the Fermi energy (Ef) is directly related to the near threshold Nb-L2,3 spectral changes. The more modest white line enhancement in the theoretical DOS is noted and discussed. Nb-K-edge XANES are also discussed in terms of the Nb-site p-state projected LAPW DOS. This last comparison indicates a p-state reduction near Ef upon H charging of the Nb.
- Publication:
-
Physical Review B
- Pub Date:
- February 1998
- DOI:
- 10.1103/PhysRevB.57.3881
- Bibcode:
- 1998PhRvB..57.3881R
- Keywords:
-
- 61.10.-i;
- 82.80.Fk;
- X-ray diffraction and scattering;
- Electrochemical methods