Si lll - 7 x 7 Structure

We have already discussed the determination of the Si(lll)-7 X 7 structure in Section 1.3. The example we are going to present, the Au(lll)-22 X structure, is equally interesting. 

In the case of individual Ceo molecules adsorbed on clean Si(lll)-(7 x 7) surfaces the experimental intramolecular structure compares well to ab initio calculations based on density functional theory (DFT) in spite of the covalent character of the substrate (Pascual et al, 2000). In this case a certain degree of uniaxial strain has to be considered to simulate the electronic influence of the substrate. 

The results for the apparent radius of STM images for individual states can be used to interpret experimental images directly. For surfaces with complex periodic structures, such as Si(lll)-7 X 7 and Si(lll)-5 X 5, the concept of imaging individual atomic states is a much better description than surface Bloch functions. For adatoms and defects, the individual state description is the only possible one. 

Calculate and sketch the diffraction patterns of ordered surface structures with (7 X 7) and (5x1) unit cells on the Si(lll) and Pt(lOO) crystal faces, respectively. 

The (7 X 7) reconstruction on Si(l 11) is by far the most complex and most famous clean surface structure in the history of surface science. Employing the (7x7) reconstruction on Si(lll), we demonstrate how creative nature is in finding sophisticated strategies for the saturation of dangling bonds and the reduction of the surface free energy. It took more than 25 years from its discovery in 1957 by Farnsworth et al. [47] until its solution in 1985 by the dimer-adatom-staddng fault (DAS) model of Takayanagi et al. [52, 53]. 

Although Si(100) and Ge(100) undergo similar dimer reconstructions, the Ge(l 11) surface reconstructions differ from those of Si(lll). As described above, Si(lll) reconstructs into a (7 x 7) structure that contains 49 surface atoms in the new unit cell. Ge(lll) is found in various reconstructed forms depending on surface preparation, but the most common reconstruction under vacuum is Ge(lll)-c(2 x 8) [51-53]. This structure involves charge transfer from adatoms to restatoms [5]. On the other hand, most of the passivation and functionalization studies reviewed here lead to the Ge(lll)-1 x 1 surface structure. This structure, in which the surface Ge atoms retain their bulk positions, can be achieved by hydrogen, chlorine, or alkyl termination of the surface (discussed below). The structure is analogous to that for H-terminated Si(lll). 

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