Formation of hydroxyl and water layers on MgO films studied with ambient pressure XPS

To understand the interaction of water with MgO(100), a detailed quantitative assessment of the interfacial chemistry is necessary. We have used ambient pressure X-ray photoelectron spectroscopy (XPS) to measure molecular (H 2O) and dissociative (OH) water adsorption on a 4 monolayer (ML) thick MgO(...

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Bibliographic Details
Published in:Surface science 2011, Vol.605 (1), p.89-94
Main Authors: Newberg, John T., Starr, David E., Yamamoto, Susumu, Kaya, Sarp, Kendelewicz, Tom, Mysak, Erin R., Porsgaard, Soeren, Salmeron, Miquel B., Brown, Gordon E., Nilsson, Anders, Bluhm, Hendrik
Format: Article
Language:English
Subjects:
ADSORPTION
Assessments
CATALYSIS
CHEMISTRY
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Condensed matter: structure, mechanical and thermal properties
Cross-disciplinary physics: materials science
rheology
DISSOCIATION
Exact sciences and technology
functional nanomaterials
GEOCHEMISTRY
HUMIDITY
HYDROXYLATION
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
Magnesium oxide
MAGNESIUM OXIDES
Mathematical models
OXIDES
Physics
Pressure
REACTION KINETICS
Relative humidity
SPECTRA
Surface chemistry
THICKNESS
WATER
X-RAY PHOTOELECTRON SPECTROSCOPY
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Summary:To understand the interaction of water with MgO(100), a detailed quantitative assessment of the interfacial chemistry is necessary. We have used ambient pressure X-ray photoelectron spectroscopy (XPS) to measure molecular (H 2O) and dissociative (OH) water adsorption on a 4 monolayer (ML) thick MgO(100)/Ag(100) film under ambient conditions. Since the entire 4 ML metal oxide (Ox) film is probed by XPS, the reaction of the MgO film with water can be quantitatively studied. Using a multilayer model (Model 1) that measures changes in Ox thickness from O 1s (film) and Ag 3d (substrate) spectra, it is shown that the oxide portion of the MgO film becomes thinner upon hydroxylation. A reaction mechanism is postulated in which the top-most layer of MgO converts to Mg(OH) 2 upon dissociation of water. Based on this mechanism a second model (Model 2) is developed to calculate Ox and OH thickness changes based on OH/Ox intensity ratios from O 1s spectra measured in situ, with the known initial Ox thickness prior to hydroxylation. Models 1 and 2 are applied to a 0.15 Torr isobar experiment, yielding similar results for H 2O, OH and Ox thickness changes as a function of relative humidity.
ISSN:0039-6028
1879-2758
DOI:10.1016/j.susc.2010.10.004