Interaction of Water with Ordered Theta-Al₂0₃ Ultrathin Films grown on NiAl(100)
The structure of an ordered, ultra thin θ-Al₂0₃ film grown on a NiAl(100) single crystal surface was studied by Auger electron spectroscopy (AES), X-Ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED), and its interaction with water was investigated with temperature programmed desorption (TPD), and XPS. Our results indicate that H₂O adsorption on the θ-Al₂0₃/NiAl(100) surface is predominantly molecular rather than dissociative. For θH₂O< 1ML (ML=monolayer), H₂O molecules were found to populate Al³⁺ cation sites to form isolated H₂O species aligned in a row along the cation sites on the oxide surface with a repulsive interaction between them. For θH₂O> 1ML, H₂O overlayers were observed to form three dimensional ice multilayers where water molecules start occupying both cationic and anionic adsorption sites on the oxide surface allowing the formation of hydrogen boding. A small extent of H₂O dissociation was observed to occur on the θ-Al₂0₃/NiAl(100) surface which was attributed to the presence of a low concentration of surface defects. Titration of these defect sites with absorbed H₂O molecules revealed an estimated defect density of ~0.-5 ML for the θ-Al₂0₃/NiAl(100) system consistent with the ordered nature of the synthesized oxide film.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15016144
- Report Number(s):
- PNNL-SA-44490; 6694; KC0302010
- Journal Information:
- Journal of Physical Chemistry B, 109(8):3431-3436, Journal Name: Journal of Physical Chemistry B, 109(8):3431-3436 Journal Issue: 8 Vol. 109; ISSN 1520-6106
- Country of Publication:
- United States
- Language:
- English
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