Surface crystallography. Diffraction techniques

Many such techniques have been developed and used. Low-Energy Electron Diffraction, in which electrons are elastically scattered off a surface, has been the most successful among those for surface crystallography. Inelastically scattered electrons also... 

So far, only a very few adsorbed molecular structures have been analyzed by surface crystallography. The first system studied in detail was acetylene adsorbed on the (111) crystal face of platinum. We shall discuss the complex adsorption and structural characteristics of this small organic molecule in some detail as it reveals the unique surface bonding arrangements that are possible and points to the importance of the use of additional techniques to complement the diffraction information. 

If we limit ourselves to observed LEED patterns, we find that over the years about 2000 ordered structures have been reported./202/ Among these, perhaps 180 have been structurally solved by various techniques of surface crystallography. Intensity analyses of low-energy electron diffraction have contributed about 150 of these. The remaining 30 structures were obtained primarily with ion scattering (MEIS, HEIS), SEXAFS or photoelectron diffraction (NPD, ARXPS). 

Some experimental techniques [e.g., low-energy electron diffraction (LEED)-surface crystallography] can detect the structural changes that occur on both sides of the surface chemical bond. However, most currently used techniques are only capable of detecting the structural changes that occur on the adsorbate side (e.g., infrared spectroscopy) or on the substrate side (e.g., electron microscopy). As a result, we often gain only incomplete information about the surface chemical bond, leading to a one-sided molecule-centric or surface-centric view of the adsorbate-surface compound that is produced. 

A full understanding of a material or a process may require the use of several complementary techniques. For example, electron diffraction in the TEM combined with FTIR and Raman spectroscopies can unequivocally determine what polymorph of Si02 is present in a sample. For example, AES can give us the composition of the surface of a sample, AFM can give us the surface morphology, and RHEED can give us the surface crystallography. 

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