Abstract
Both the chemical shift and quadrupole coupling tensors for N and Al in the wurtzite structure of aluminum nitride have been determined to high precision by single-crystal NMR spectroscopy. A homoepitaxially grown AlN single crystal with known morphology was used, which allowed for optical alignment of the crystal on the goniometer axis. From the analysis of the rotation patterns of N () and Al (), the quadrupolar coupling constants were determined to kHz, and MHz. The chemical shift parameters obtained from the data fit were ppm and ppm for N, and (after correcting for the second-order quadrupolar shift) ppm and ppm for Al. DFT calculations of the NMR parameters for non-optimized crystal geometries of AlN generally did not match the experimental values, whereas optimized geometries came close for Al with MHz, but not for N with kHz.
Highlights
Aluminum nitride, AlN, is industrially used as a substrate for semiconductor devices such as ultraviolet LEDs, and is the preferred starting material for the synthesis of chemically inert lightweight ceramics with excellent mechanical properties, such as SiAlONs [1,2]
A single crystal of aluminum nitride with approximate dimensions of 5 × 5 × 4 mm was used for the single-crystal Nuclear magnetic resonance (NMR) experiments
Representative 27 Al NMR spectra are shown in Figure 2a, with the full rotation pattern over 180o shown in Figure 2b, which was obtained by rotating the crystal counterclockwise in steps of 15◦
Summary
AlN, is industrially used as a substrate for semiconductor devices such as ultraviolet LEDs, and is the preferred starting material for the synthesis of chemically inert lightweight ceramics with excellent mechanical properties, such as SiAlONs [1,2]. For characterization of a multi-component system, it is crucial to know the exact NMR-interaction parameters of the detected nuclei in the various components, in order to correctly assign and distinguish the NMR signals arising from them. Molecules 2020, 25, 469 for the determination of the NMR-interaction parameters, which in the solid state take the form of second-rank tensors [6], is via NMR spectroscopy of single crystals [7]. We present the determination of the full chemical shift tensor δ and quadrupole coupling tensor Q for 27 Al (I = 5/2) and 14 N (I = 1) in hexagonal aluminum nitride by means of single-crystal
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