Semiconductors NQCCs

Earlier sections of this review have already discussed results for quadrupolar nuclei in certain connections for Knight shifts (Sects. 3.4.3 and 3.4.4), for electric-field (Stark) effects upon NQCCs (Sect. 3.1), for measurements of NQCCs in GaN by static NMR and the effects of strain upon NQCCs (Sect. 3.2.1), for obtaining exchange couplings by MAS-NMR (Sect. 3.2.2), and for characterizing polytypes and defects in cubic polytypes by chemical shifts and NQCCs obtained from MAS-NMR (Sect. 3.3.2). This section will give some further examples of information about semiconductors obtained from the NMR of quadrupolar nuclei (see also [18]). 

The study of local or long-range ordering in semiconductor alloys based upon the effects on NQCCs has been carried out in a number of cases. These studies are analogous to the study of ordering in In Ga P by means of the chemical shift interaction, as described in Sect. 3.3.1. 

From a very general outlook, one can argue that the NMR studies of quadrupolar nuclei present in nanoscale semiconductors should offer a more incisive look into the chemical and electronic structure than do studies of spin-1/2 nuclei. The rationale is that quadrupolar nuclei can report on the same chemical, hyperftne, or Knight shifts and dipolar or indirect couplings as observed for spin-1/2 nuclei, but also provide an additional dimension of information in terms of the NQCC and associated EFGs. Although not yet reported, DFT calculations of both chemical shifts and NQCC values for the same nuclei in nano-semiconductors should provide a more stringent comparison of theoretical and experimental results, particularly if the two parameters can be correlated experimentally, as seems feasible. 

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