Charge dangling bond

Fig. 2 Visualization of the electrostatic potential emanating from a point source for a styrene chain on H Si(100). (a) With negatively charged dangling bonds labeled DBl and DB2. The prominent white bar is a line of surface-bound molecules. At increased sample bias of—2.4 V, molecular p-states are turned on , causing molecules to appear bright (topographically elevated) and of nearly constant height across...

The incorporation of phosphorus yields fourfold-coordinated P atoms, which are positively charged, as phosphorus normally is threefold coordinated. This substitutional doping mechanism was described by Street [52], thereby resolving the apparent discrepancy with the so-called S N rule, with N the number of valence electrons, as originally proposed by Mott [53]. In addition, the incorporation mechanism, because charge neutrality must be preserved, leads to the formation of deep defects (dangling bonds). This increase in defect density as a result of doping explains the fact that a-Si H photovoltaic devices are not simple p-n diodes (as with crystalline materials) an intrinsic layer, with low defect density, must be introduced between the p- and n-doped layers. 

A set of simple physical and chemical principles can be used to understand and predict the surface reconstruction or faceting, which occurs on oxide surfaces.8,9 These include (1) autocompensation of stable surfaces, (2) rehybridization of the dangling bond charge density, (3) formation of an insulating surface, (4) conservation of near-neighbor bond lengths (which minimize the formation of surface strain fields), and (5) surface kinetic factors. We shall briefly discuss all of these factors governing the surface reconstruction of metal oxide. 

Once a particular surface structure has been determined to be stable (i.e., autocompensated), the primary factor determining the nature of the surface reconstruction is the energy that can be gained by rehybridizing the surface dangling bond charge density in response to the reduced coordination at the surface. As a consequence, a charge transfer between the atoms at the surface takes place and this results in the formation of new bonds between surface atoms adsorbed to the surface (also known as adatoms). The formation of new bonds on the surface leads to different chemical and physical properties at the surface.11... 

Fig. 4.15. Contours of constant charge density for Si(lll). The occupied portion of the dangling-bond surface state on Si(lll) is shown. Dots locate nuclei of surface atoms, the vacuum is above, and the charge density is in a.u.X lOL (Reproduced from Appelbaum and Hamann, 1976, with permission.)...

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