硅微粒表面氢的DNP-NMR
DNP-NMR of surface hydrogen on silicon microparticles
摘要：
动态核极化（DNP）增强的核磁共振（NMR）为研究晶体和非晶体材料表面的局部原子环境提供了一条很有前途的途径。我们利用未成对电子，由于缺陷接近表面的硅微粒hyperbonding相邻的$^{1}$ H核。在3.3 T和4.2 K下，我们观察到两个质子峰的存在，每个峰的线宽约为5 kHz。回波实验表明两个峰的$\sim 150-300$ Hz的均匀线宽，表明两种环境中质子的稀疏分布。在10 ppm处的低场峰位于质子NMR的典型化学位移范围内，并且被发现在重复测量中相对稳定。发现高场峰的位置在-19和-37 ppm之间变化，远超出典型质子NMR位移的范围，并且指示高度的化学屏蔽。还发现在不同的实验运行中，高场峰的强度显着不同，表明弱结合的物种。这些结果表明，氢位于两个不同的微观环境中的这些Si颗粒的表面上。
英文摘要：
Dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) offers a promising route to studying local atomic environments at the surface of both crystalline and amorphous materials. We take advantage of unpaired electrons due to defects close to the surface of the silicon microparticles to hyperpolarize adjacent $^{1}$H nuclei. At 3.3 T and 4.2 K, we observe the presence of two proton peaks, each with a linewidth on the order of 5 kHz. Echo experiments indicate a homogeneous linewidth of $\sim 150-300$ Hz for both peaks, indicative of a sparse distribution of protons in both environments. The downfield peak at 10 ppm lies within the typical chemical shift range for proton NMR, and was found to be relatively stable over repeated measurements. The upfield peak was found to vary in position between -19 and -37 ppm, well outside the range of typical proton NMR shifts, and indicative of a high-degree of chemical shielding. The upfield peak was also found to vary significantly in intensity across different experimental runs, suggesting a weakly-bound species. These results suggest that the hydrogen is located in two distinct microscopic environments on the surface of these Si particles.
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