Structure of the Hydrogen Stabilized MgO(111)-(1x1) Polar Surface: Integrated Experimental and Theoretical Studies
2005
The surface structure of MgOs111d-s1 3 1d bulk and thinned single crystals have been investigated by transmission and reflection high-energy electron diffraction, low-energy electron diffraction sLEEDd, and x-ray photoelectron and Auger electron diffraction. The s1 3 1d polar surface periodicity is observed both after 800 °C annealing in air and also after oxygen plasma cleaning and annealing in ultrahigh vacuum. The x-ray photoelectron spectroscopy and diffraction results were analyzed by simulations based on path-reversed LEED theory and by first-principles calculations to help distinguish between different mechanisms for the stabilization of this extremely polar oxide surface: s1d stabilization by adsorption of a hydrogen monolayer; maintaining the insulating nature of the surface and s2d stabilization of the clean O or Mg terminated 1 3 1 surface by interlayer relaxations and two-dimensional surface metallization. The analysis favors stabilization by a single OH layer, where hydrogen sits on top of the O ions with O-H bond distance of 0.98A. The in-plane O and Mg positions fit regular rocksalt sites, the distance between the topmost O and Mg plane is 1.04 A, contracted by ,14% with respect to bulk MgO distance of 1.21 A, while the interlayer separation of the deeper layers is close to that of bulk, contracted by less than 1%. The presence of a monolayer of H associated with the terminal layer of oxygen reduces significantly the surface dipole and stabilizes the surface.
Keywords:
- Nuclear magnetic resonance
- Atomic physics
- Adsorption
- Auger electron spectroscopy
- Monolayer
- Electron diffraction
- X-ray photoelectron spectroscopy
- Low-energy electron diffraction
- Reflection high-energy electron diffraction
- Inorganic chemistry
- Physics
- Electron density
- Analytical chemistry
- Condensed matter physics
- X-ray standing waves
- Hydrogen
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