Chemical structure and bonding characteristics of metal hydrogen systems studied by the surface analytical techniques SIMS and XPS

Abstract

Secondary ion mass spectrometry (SIMS) as well as photoelectron spectroscopy (XPS) are powerful tools for studying special properties of metal hydrogen systems and the interaction of hydrogen and metals. SIMS experiments have now also been extended to transition metal hydrogen systems with small hydrogen solubilities by using intelligent mass spectra accumulation. As known from studies on other metal hydrogen systems (V–H, Nb–H etc.) the cluster ion Me 2 H + is particularly characteristic for transition metal hydrogen systems. In AB 5 -type alloy hydrogen systems a quite different behavior is observed. We have focussed our attention on studying the properties of the LaNi 5 -alloy with nickel partially substituted by Al or Ag. The mass spectra, especially the negative ones, show a strong Ni–H, a weaker Ag–H and almost no Al–H bond, which explains the decrease in hydrogen storage capacity when going from pure LaNi 5 to LaNi 5− X Ag X and LaNi 5− X Al X . Pressure–concentration like isotherms are obtained for the LaNi 5− X Al X D Y system by SIMS with highest spectral purity when applying a synchronous in situ gasvolumetric hydrogen charging procedure during the SIMS analysis under Ar + ion bombardment. XPS studies on metal hydrogen systems yield valuable information concerning chemical and physical properties, which are complementary to the SIMS results. A hydrogen induced chemical shift and changes in the line shape of the valence band and the core electron levels are observed in LaNi 5 H Y photoelectron spectra if H 2 + ion implantation is used as an alternative hydrogen charging technique. The XPS results indicate the existence of a Ni–H bond in excellent agreement with the SIMS measurements.