Electron density, phosphorus nucleus

More sensitive ESR measurements over a wider magnetic field range find additional resonances in phosphorus- and arsenic-doped material, examples of which are shown in Fig. 5.11. The extra lines (two for phosphorus and four for arsenic) are due to the hyperfine interaction of the electron bound to the donor (Stutzmann and Street 1985). The ESR spectra have exactly the number of lines and relative intensities expected from the nuclear spins of and for phosphorus and arsenic atoms. The splitting of the lines, is proportional to the electron density at the nucleus and is a measure of the localization length, r, of the donor. 

Preliminary studies have also been carried out on solutions of thallium compounds (see Table XIII). In every case studied, the enhancement was positive for both thallus and thallic compounds. However it was found that for thallus compounds the presence of free radical greatly broadened the n.m.r. signal, and that the observed enhancements were much larger than for thallic compounds. A similar explanation to that suggested for phosphorus has been used to explain this behaviour. In the thallus compounds the electron spin density from the free radical can be transmitted to the nucleus via the lone pair of electrons in the 65 orbital. In thallic compounds this lone pair is no longer available, and the unpaired electron density is then assumed to be transmitted via an indirect mechanism. 

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