Chemical-state studies of Zr and Nb surfaces exposed to hydrogen ions.

Abstract

Surface chemical states were studied for Zr and Nb metals exposed to 8-keV hydrogen molecular ions. X-ray photoemission spectroscopy (XPS) measurements revealed that chemical shifts of the binding energies for the ion-implanted Zr from the metallic states are 0.6--1.4 eV, consistent with the core-line shifts for thermally synthesized ${\mathrm{ZrH}}_{1.64}$. In the case of the ion-implanted Nb, the corresponding shifts are 0.6--0.8 eV, in good agreement with those for thermally synthesized ${\mathrm{NbH}}_{0.86}$. On the other hand, the ion implantation provided XPS spectra with a distinct photopeak attributable to a metal 4d--H 1s bond near the Fermi level, 3.4 eV for Zr and 4.6 eV for Nb, respectively. The peak positions are \ensuremath{\sim}2.5 eV lower than those calculated previously for the dihydrides. The photopeaks grew upon thermal annealing to 610 \ifmmode^\circ\else\textdegree\fi{}C. The observations are discussed in relation with the peculiarity of hydrogen sites in the crystal lattice and partial recovery of the ion-induced surface damage.