Surface structure models

Manceau, A. Drits,V.A. (1993) Local structure of ferrihydrite and feroxyhite by EXAFS spectroscopy. Clay Min. 28 165-184 Manceau, A. Gates, W.P. (1997) Surface structural model for ferrihydrite. Clays Clay Min. 45 448-460... 

Most surface structural studies combine results from several different surface science techniques applied to the same system. For an approach based on model calculations to be successful, it is necessary to construct reasonable structural models of surfaces. The application of techniques which cannot give explicit information on the arrangement of atoms in the near-surface region is often necessary to develop good surface structural models. 

Here, A is the area of the surface unit-cell, and Go surf and Gsurf are the Gibbs free energies of the oxidized and clean surface, respectively, juq and jiiM are the chemical potentials of oxygen and metal atoms, and No is the number of oxygen atoms contained in the oxidized surface structure for which AG jjo) is computed. Finally, AIVm is the difference in the number of metal atoms between the reference clean surface and the oxidized surface structural model. 

After a C(2 x 2)-NH2 layer is formed on W(IOO) by flashing a room temperature NHg deposit to 525°C, more NH3 can be adsorbed on the cooled surface. The C(2 x 2) half-monolayer becomes a (1 X 1) full mono-layer of NHa after a second heating to 525°C. Thermal degradation of this W(100)-(l X l)-NHa causes appearance first of a (6x6)-NH2, then the C(2 X 2)-NH2 and finally a clean surface. Structural models of the transformation via (6 X 6) were not given by Estrup and Anderson. 

The most detailed calculations, in relation to the different surface structure models, have been performed very recently by Chadi [193, 194] with the tight-binding method, and Chalikowsky and Cohen [195] using self-consistent pseudo-potentials. The first important point is that both calculations show a complete absence of intergap states, both filled and empty, for a preferred, although not unequivocally established surface structure in which the angle of inward rotation of the Ga atoms is... 

Manceau A, Drits VA, Silvester E, Bartoli C, Lanson (1997) Structural mechanism of Co(II) oxidation by the phyllomanganate, Na-buserite. Am Mineral 82 1150-1175 Manceau A, Gates W (1997) Surface structural model for ferrihydrite. Clays Clay Miner 43 448-460 Manceau A, Gorshkov Al, Drits VA (1992) Structural chemistry of Mn, Fe, Co, and Ni in Mn hydrous oxides. II. Information from EXAFS spectroscopy, electron and X-ray diffraction. Am Mineral 77 1144-1157... 

The silica gel framework is ruptured when water is split out. The same processes can lead to a loosening of the surface. Structural models, based on the crystal structure of the Si02-modification do not therefore fully depict the surface fine structure. These relationships are best expressed by using three concepts ... 

Pape, H., Worthington, P.F., 1983. A surface-structure model for the electrical conductivity of reservoir rocks. In Trans. 8th Europ. Logging Symp. SPWLA. Paper Z. 

Ti04Polyhedra TiO Polyhedra TiO Polyhedra Sr Atom TiAtom OAtom Fig. 4 Top to bottom SrTiOs (111) surface structure models 3 through 8 considmrd in [24]... 

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