Dangling O-H bond

Clearly, one must truncate the number of solvation shells to limit the number of water molecules to some reasonable value. But just how many water molecules are necessary to obtain bulk liquid water Certainly a calculation of the solute and just the first solvation shell does not capture the effect of bulk water. Without the next solvation shell, the water molecules in the first shell do not have these neighboring water molecules to interact with via hydrogen bonding. Instead, the water molecules might seek out additional favorable interactions with the solute or be forced to have some dangling O-H bonds and lone pairs. 

All silicon atoms which are not involved in Si-O bonding are 4-fold coordinated, with all dangling (non Si-Si) bonds taken up by Si-H bonds. 

Enokida et al. (1991) measured hole mdbilities of PMPS before and after ultraviolet exposures. The exposures were of the order of 1 erg/s-cm2. Prior to the exposures, the mobilities were approximately 10-4 cm2/Vs and weakly field dependent. Following the exposures, a decrease in the mobility was observed. Under vacuum exposure conditions, a decrease of approximately 40% was observed for a 1 h exposure. Under atmospheric conditions, however, the decrease was approximately a factor of 4. Enokida et al. attributed the decrease in mobility to the formation of Si-O-Si bonds in the Si backbone chain. A similar study of PMPS was described by Naito et al. (1991). While the field and temperature dependencies of the mobility were not affected by the ultraviolet exposures, the dispersion in transit times increased significantly. The change in dispersion could be removed by subsequent annealing. The authors attributed the increase in transit time dispersion to a reduction in the hole lifetime, induced by Si dangling bonds created by the ultraviolet radiation. 

Such variation in the density of surface states can be explained by the existence of defect centers associated with dangling bonds arising from the discontinuity of Si—O or Si—H bonds and oxygen danghng bonds (—O) [20]. For strucmres with d = 5.0 nm, the increase in the density of surface states may be due to the simultaneous formation of two types of defects, trivalent Si atoms (=Si.) and oxygen dangling bonds (—O) [21]. The defects arise when the Si—O bonds cleave under UV irradiation, as proven by the decrease in the vlo absorption band of Si-0 modes (see Fig. 6.2). 

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