INTERACTION OF WATER WITH NIA1(110) - A TPD, EELS, AND XPS INVESTIGATION

The interaction of water with NiAl(110) has been investigated with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and high resolution electron energy loss spectroscopy (EELS). Exposure of NiAl(110) to H2O at 123 K results in primarily adsorbed H2O, but the spectroscopic data suggests that OH(ad) may also be present. TPD shows that at low exposures, water desorbs from NiAl(110) at similar to 190 K, and hydrogen desorbs between 300 and 400 K. The low temperature of H2O desorption suggests that a weakly bound molecular state exists on NiAl(110). The majority of the chemisorbed H2O, however, is more strongly bound, and dissociates to form an OH(ad) overlayer upon heating to 173 K. Our results suggest that while the adsorbed water is sensitive to the hybridized electronic structure of NiAl, the more strongly bound OH(ad) (and O-(ad)) species appear to adopt a more atomic-like bonding to the Al component. The OH(ad) overlayer shows some dissociation by 250 K, and by 500 K the entire overlayer has decomposed, forming an Al2O3 layer.