Surface structure determination

The determination of the atomic structure of surfaces is the cornerstone of surface science. Before the invention of STM, various diffraction methods are applied, such as low-energy electron diffraction (LEED) and atom beam scattering see Chapter 4. However, those methods can only provide the Fourier-transformed information of the atomic structure averaged over a relatively large area. Often, after a surface structure is observed by diffraction methods, conflicting models were proposed by different authors. Sometimes, a consensus can be reached. In many cases, controversy remains. Besides, the diffraction method can only provide information about structures of relatively simple and perfectly periodic surfaces. Large and complex structures are out of the reach of diffraction methods. On real surfaces, aperiodic structures such as defects and local variations always exist. Before the invention of the STM, there was no way to determine those aperiodic structures. 

The invention of STM completely changed the situation. As of the end of 1991, with the help of STM, combining with other techniques, a large number of surface structures have become known. 

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Woodruff D P, Cowie B C C and Ettem a A R H F 1994 Surface structure determination using x-ray standing waves a simple view J. Rhys.. Condens. 6 10 633—45... 

B1.23 Surface structural determination particle scattering methods... 

Kim C, Hefner C and Rabalais J W 1997 Surface structure determination from ion scattering images Surf. Sc/. 388 LI 085-91... 

Tidsweii i M, Lucas C A, Markovic N M and Ross P N 1995 Surface structure determination using anomaious x-ray scattering Underpotentiai deposition of copper on Pt(111) Phys. Rev. B 51 10 205-8... 

Surface structure determination 325—331 Suspension springs 244—248 Takayanagi model See DAS model Tamm states... 

In this chapter, the objective is to illustrate some of the structural phenomena associated with adsorbate bonding at surfaces and to show how (experimental) quantitative surface structure determination can provide insight into the nature of... 

Molecular adsorbates provide an increasingly complex set of challenges to surface structure determination, the complexity growing steeply with the number of atoms within the molecule. A special problem is also presented by hydrogen atoms which are present in the majority of chemically interesting molecules, but to which all... 

Feldman, L. C. "MeV Ion Scattering for Surface Structure Determination," in Surface Science Recent Progress and Perspectives CRC Press, Inc. Cleveland, Ohio, 1981. 

This method is undisputedly the most important innovation in this field since the advent of the surface science founding methods AES and XPS in the 1960s [14]. It has revolutionized surface structure determination and is an extremely powerful method for investigating 2D molecular pattern formation. Applications also include biology, electrochemistry, solid state physics, as well as atomic and molecular manipulation. Although most of the studies... 

Van Hove M.A., Weinberg W.H., Chan C.M., Low-Energy Electron Diffraction Experiment, Theory and Surface Structural Determination, Springer, Berlin, 1986. 

Simplifications can be brought about whenever the surface structure has symmetries. Point-group symmetries help moderately to reduce the matrix dimensions. On the other hand, two-dimensional periodicity can help drastically by reducing the number N to the number of atoms within a single two-dimensional unit cell with a depth perpendicular to the surface of a few times the electron mean free path. For surface crystallography this is, however, not yet sufficient, because surface structural determination requires repeating such calculations for hundreds of different geometrical models of the surface structure. 

In the previous two sections we have discussed the semiempirical extended Hiickel theory and the SCF-Xa-SW method. We have detailed the advantages and disadvantages of these methods for surface structure determination. 

In this section, we present and discuss the accumulated results of surface structure determination. We give a comprehensive tabulation of published results. Only those structures which provide three-dimensional geometrical... 

Other techniques used in surface structure determination include extended X-ray absorption fine structure (EXAFS), ion scattering, electron forward focusing, and helium atom diffraction. 

An additional aspect of surface structure determination involves the relationship between swface structure and reactivity. The study of adsorbates on well ordered solids constitutes much of the structural work being carried out today. When an atom or molecule adsorbs on a clean substrate, its equilibrium position is determined by its interactions with the surface atoms, and its interactions with neighboring adsorbates. For physically adsorbed species, adsorbate adsorbate interactions can equal the interaction between the adsorbate and substrate and affect the structure of the overlayer. However the adsorbate adsorbate interactions are typically small when compared to the forces in chemical bonds formed upon adsorption and adsorbate-substrate interactions dominate in chemisorbed systems. 

M.A. van Hove. W.H. Weinberg and C.-M. Chan, Low-Energy Electron Diffraction. Experiment. Theory and Surface Structure Determination, Springer (1986). (Comprehensive overview of LEED). 

Overbury SH, Mullins DR, Paffett MT, Koel BE (1991) Surface structural determination of Sn deposited on Pt(lll) by low energy alkali ion scattering. Surf Sci 254 45... 

Feidenhans l R (1989) Surface structure determination by x-ray diffraction. Surf Sci Rep 10 105... 

Thompson KA, EUis WP, Taylor TN, Valone SM, Maggiore CJ (1983) Surface structural determination of UOj(III) using meV ions. Nucl Inst Meth Phys Res 218 475... 

Tabulations of some surface structures may be found in a review by Van Hove and coworkers (Van Hove et al., 1989) and the reviews by Watson that compare the results of surface structure determinations utilizing different crystallographic techniques (Watson, 1990, 1992). Van Hove has also published a recent review of crystal surface structure, without the tabular presentation of the structural data (Van Hove, 1992). Van Hove and Somorjai have reviewed surface structure from the point-of-view of adsorbate induced restructuring of surfaces (Van Hove and Somorjai, 1989). Ohtani and coworkers have listed all observed overlayer structures and surface symmetries, albeit without any reference to the detailed surface structure (Ohtani et al., 1987). 

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