Deanna Franke

Heteronuclear X-Y double quantum MAS NMR in crystalline inorganic solids. Applications for indirect detection and spectral editing of rare-spin resonances.

Heteronuclear double quantum MAS NMR experiments in the solid state, involving pairs of highly abundant 31P spins and the rare spins 113Cd, 77Se, and 29Si, are described for the three crystalline compounds CdSiP2, CdGeP2, and Ag7PSe6. These experiments offer the opportunity of indirectly detecting the rare-spin resonance via chemical shift evolution of heteronuclear double quantum coherence. For suitable cases, this method results in significantly enhanced detection sensitivities. Criteria for favorable indirect detection experiments are established. Besides offering high sensitivity, the pulse sequence also acts as a heteronuclear double quantum filter, hence providing heteronuclear correlation and useful spectral editing for peak assignments.

Spectral editing in MAS NMR of aprotic solids 31P113Cd cross-polarization and heteronuclear double-quantum filtering studies in II-IV-V2 semiconductor alloys

Magic-angle-spinning NMR spectra of aprotic solids, ceramics and glasses frequently suffer from poor site resolution due to wide chemical shift distribution effects. In such cases, cross-polarization and heteronuclear double-quantum filtering experiments involving nuclei other than 1H offer unique spectral editing capabilities. The utility of such assignment techniques for examining site populations in semiconductor alloys is demonstrated for the chalcopyrite systems CdGeAs2-xPx, CdSiAs2-xPx and ZnxCd1-xGeP2. The results permit a distinction between local and non-local effects on experimental chemical shift trends and reveal that compositional dependences observed in these alloys are dominated by non-local chemical shift contributions.

Solid State NMR Chemical Shifts of Chalcogenides and Pnictides

Chemical shift data available in the literature on binary II-VI and III-V semiconductors and semiconductor alloys and new data obtained on II-IV-V2 chalcopyrite semiconductors and their respective alloys are reviewed and discussed in terms of current molecular orbital descriptions for solids. The chemical shift trends observed for the 33S, 77Se, and 125Te resonances in binary II-VI compounds are satisfactorily explained in terms of the Bond Orbital Model (BOM) developed by Harrison, whereas the 113Cd chemical shift trends observed for the cadmium chalcogenides disagree with BOM predictions. For the III-V compounds, the BOM fails to account for the experimentally observed chemical shift trends. Here, the two-electron bond orbital model including the effect of inter-electronic interactions provides a much better description. In terms of this model, the major chemical shift differences seen along homologous series are due to differences in anion-cation overlap rather than bond ionicity. Applications of this model for explaining chemical shift trends in II-IV-V2 chalcopyrite semiconductors and II-VI, III-V, and II-IV-V2 semiconductor alloys are discussed.

Quantitative evaluation of gallium phosphide samples prepared from rapid solid state metathesis : solid state 31P and 69Ga magic angle spinning NMR strategies

Abstract Quantitative solid state nuclear magnetic resonance (NMR) techniques are capable of evaluating the crystalline quality of III-V semiconductor preparations. To this end, an analytical protocol consisting of magic angle spinning lineshape analysis, spin counting studies, and quadrupolar nutation NMR has been established, allowing sample comparisons on a numerical scale. This protocol is applied to a suite of gallium phosphide (GaP) samples prepared by a novel rapid solid state metathesis route from gallium halide and sodium phosphide. The results show that the quality and crystallinity of the GaP product phase depends senstively on the gallium halide precursor used, with GaF3 resulting in the highest-quality material.