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

John T. Newberg, David E. Starr, Susumu Yamamoto, Sarp Kaya, Tom Kendelewicz, Erin R. Mysak, Soeren Porsgaard, Miquel B. Salmeron, Gordon E. Brown, Anders Nilsson, Hendrik Bluhm

Research output: Contribution to journalArticlepeer-review

122 Citations (Scopus)


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 (H2O) 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 H2O, OH and Ox thickness changes as a function of relative humidity.

Original languageEnglish
Pages (from-to)89-94
Number of pages6
JournalSurface Science
Issue number1-2
Publication statusPublished - 2011 Jan


  • Catalysis
  • Geochemistry
  • Magnesium oxide
  • Surface chemistry


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