Bond-creating reconstructions

Bond-Breaking or Bond-Creating Reconstruction of Eiementai Surfaces... 

Chemical and bond-creating reconstructions that go beyond the range accessible by different terminations of the bulk stmcture have been found on SiC(OOOl) and SiC(lll) surfaces. They are induced by deposition of Si on the SiC surface and subsequent annealing. On the Si-rich side, the surface phase diagram begins with a (3 X 3) reconstruction, which is characterized by a Si adlayer terminated by an adatom tetrahedrally supported by three extra Si atoms [123, 124]. The reconstruction model is shown in the top and side views in Figure 4.44a,b. Chemically the reconstruction involves 13/9 monolayers of Si on top of an already Si-terminated bulk. Geometrically, the Si adlayer compensates the lattice mismatch of about 20% between SiC and Si, with the result that instead of a bilayer one... 

Figure 4.2 Side view of surface reconstruction types with different periodicities in the surface and the bulk, A and a, respectively. The reconstruction can be (a) displacive, (b) bond breaking, or (c) bond creating. Panel (d) visualizes a bcc(210) surface that has faceted into (100) and (110) oriented patches.

An intriguing example for bond-creating chemical reconstructions is the GaAs(lOO) surface. Also, in this orientation, the surface is composed of alternating layers of Ga and As, and thus the surface stoichiometry depends on the actual termination even in bulk truncation, similar to the cases of ordered alloys. Surface phases with varying chemical termination can be prepared by changing the parameters in molecular beam epitaxy [118]. Different from the case of Si(lOO),... 

In the discussion so far, an ideal termination of the bulk crystal has been assumed at the surface that is, the positions of atoms in the surface have been assumed to be the same as what they would have been in the bulk before the surface was created. This may not be true. Reconstruction, a rearrangement of atoms in the surfrce and near-surface layers, occurs frequently. It is caused by an attempt of the surface to lower its free energy by eliminating broken bonds. The atomic layers par-... 

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