Behavior of zirconium surfaces in the presence of oxygen, nitrogen, and hydrogen containing adsorbates

As part of an effort to address questions related to corrosion passivation in zirconium alloys, low energy electron diffraction (LEED) and temperature programmed desorption (TPD) techniques have been applied to the adsorption of water and ammonia on Zr(0001). Water adsorption at 180 K results in wat er desorption in a broad TPD feature near 625 K. Ammonia exposure at 150 an d 180 K results in the unexpected production of water during TPD near 625 a nd 525 K, respectively, and the formation of complex residual LEED patterns . Auger electron spectroscopy indicates that nitrogen remains at or near th e surface following ammonia adsorption and TPD. A phenomenological explanat ion involving a temperature-dependent dissociation probability for ammonia and nitrogen/ oxygen exchange between the surface and subsurface regions is presented to qualitatively account for these findings. (C) 2001 American V acuum Society.