Materials Science Centre, Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai 600 025, India.
J Phys Chem B. 2011 Jun 23;115(24):7766-72. doi: 10.1021/jp201367b. Epub 2011 May 26.
We have studied N-doped 6H-SiC in its pristine and Swift Heavy Ion (SHI) irradiated (150 MeV Ag(12+) ions) forms by solid state Nuclear Magnetic Resonance (NMR) at 7.01 T using (13)C and (29)Si as probe nuclei under magic angle spinning. We show that increased levels of nitrogen doping, than used before, lead to the observation of Knight shifts emanating from an increase in electron density in the conduction band, which in (13)C far exceed those in (29)Si MAS spectra. We have rationalized the differential effects in the MAS spectra and site-dependent paramagnetic shifts in terms of the nitrogen doping at the A, B, and C lattice sites. N-doping has a profound effect on (29)Si spin-lattice relaxation, and the site-dependent relaxation behavior is attributed to a difference in conduction electron properties at the different lattice sites. (29)Si T(1) measurements serve to identify the sublattice damages in SHI irradiated 6H-SiC. By determining the spin-lattice relaxation rates as a function of the SHI irradiation ion fluences, the change in relaxation behavior is correlated to the damage production mechanism. The sublattice damage leads to discernable changes in the interaction between the mobile unpaired electrons in the conduction band and the nuclear site, which profoundly influence the NMR relaxation properties. Our relaxation studies also provide evidence for site-dependent localized effects and a decrease in carrier spin density in the conduction band for the SHI irradiated 6H-SiC.
我们通过固态核磁共振（NMR）在 7.01T 下使用（13）C 和（29）Si 作为探测核，对原始和 Swift 重离子（SHI）辐照（150MeVAg（12+）离子）的 N 掺杂 6H-SiC 进行了研究。在魔法角旋转下。我们表明，与以前使用的氮掺杂水平相比，增加氮掺杂水平会导致观察到来自导带电子密度增加的 Knight 位移，在（13）C 中，这些位移远高于（29）Si MAS 光谱中的位移。我们根据 A、B 和 C 晶格位置的氮掺杂，对 MAS 光谱中的差分效应和与位置有关的顺磁位移进行了合理化解释。氮掺杂对（29）Si 自旋晶格弛豫有深远影响，与不同晶格位置的传导电子性质不同有关的位置相关弛豫行为。（29）SiT（1）测量可用于识别 SHI 辐照 6H-SiC 中的亚晶格损伤。通过确定自旋晶格弛豫率作为 SHI 辐照离子通量的函数，弛豫行为的变化与损伤产生机制相关。亚晶格损伤导致传导带中未配对电子和核位之间的相互作用发生可察觉的变化，这极大地影响了 NMR 弛豫性质。我们的弛豫研究还为 SHI 辐照 6H-SiC 中与位置有关的局部效应和传导带中载流子自旋密度的降低提供了证据。
