Hydrogen detection by SIMS: hydrogen on polycrystalline vanadium

The interaction of hydrogen with polycrystalline vanadium has been studied by SIMS and flash-desorption. Two well defined vanadium surfaces with different amounts of residual oxygen were exposed to H2-doses up to 1000 L. The investigations were carried out under UHV conditions. The experiments result in a better understanding of the vanadium-hydrogen interaction, especially with regard to the influence of residual oxygen. The residual oxygen concentration can be characterized by the O- emission; it increases with the number of 02 exposure/heating cycles. Different groups of secondary ions and flash signals, characteristic of certain chemical environments of hydrogen, could be distinguished. The ratio VH+/V+ and V2H+/V2+ proved to be typical of the direct V-H bond concentration. This can be derived from their behaviour during H2 and 02 exposure, e.g. Bulk dissolved hydrogen is indicated by a dose-depending H2 flash signal at 900 K. Bulk solution of H2 is blocked by a monomolecular oxygen layer. An additional H2 flash signal at 500 K together with increasing values of VH+/V+ and V2H+/V2+ is observed for relatively oxygen free targets after H2 exposure. The detection limit for metal-bonded hydrogen was found to be less than 100 ppm of one monolayer. (Auth.)