Abstract
The structure of an ordered, ultra-thin Al2O3 film grown on a NiAl(110) single-crystal surface and its interaction with D2O were studied by low energy ion scattering spectroscopy (LEISS), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). LEISS demonstrated that the surface was terminated by an oxygen layer, and TPD data of adsorbed D2O revealed that most of the water molecularly adsorbed onto Al2O3/NiAl(110). However, we observed that a small amount of water molecules dissociated during adsorption and/or TPD measurements, and as a consequence the alumina film thickness increased after water adsorption/desorption. These results suggest that atomic oxygen and/or hydroxyl species, which are formed by dissociation of water, interact with sub-surface aluminum atoms through defects sites and cause the increase in the alumina film thickness. In addition, due to the weak interaction between adsorbed water molecules and the alumina film, a few monolayer of water can be transformed from amorphous solid water (ASW) to crystalline ice (CI) phase, as it was seen by IRAS.
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