Dangling bonds Subject

It should be mentioned that as well as for metals the passivation of semiconductors (particularly on Si, GaAs, InP) is also a subject of intense investigation. However, the goal is mostly not the suppression of corrosion but either the fonnation of a dielectric layer that can be exploited for devices (MIS stmctures) or the minimization of interface states (dangling bonds) on the semiconductor surface [63, 64]. 

There are two kinds of surface states entrapment and polarization. The dangling bonds or surface impurities are subject to polarization, which add impurity states within the Eq of semiconductors. Termination of the dangling bonds by H adsorption could minimize the impurity states. The other is the entrapment in the relaxed surface region, which offsets the entire band strucmre down associated with Eq enlargement and the presence of band tails. 

Film morphology can also be modified because fast particle bombardment can damage the substrate surface and create local sites with more dangling bonds. These are relatively reactive with adatoms, having extra bonds available, and can serve as preferential nucleation sites. At the same time, disruption of clusters increases the critical nucleus size making nucleation more difficult. These two effects do not cancel each other out because early and late nucleation are subject to different constraints. The first nuclei to form do so in the absence of sinks for adatoms. Therefore the adatom density can increase until the adatom supersaturation favors nucleation enough to counteract the disruption of clusters by fast particles. At the same time, the creation of favored nucleation sites also contributes to favoring nucleation. On balance, fast particle bombardment may accelerate the formation of the early nuclei. 

A fourth approach utihzes ONIOM, a computational method devised by Morokuma. The method was intended to dissect a large molecule into portions. One portion is subject to quantum mechanical computation. Further portions are treated by molecular mechanics. In dissecting a molecule by breaking bonds, the Morokuma method caps the dangling valences with light atoms as hydrogens. 

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