Department of Physics, Ben-Gurion University of the Negev, Be'er Sheva 84105, Israel.
J Phys Condens Matter. 2013 Jun 19;25(24):245303. doi: 10.1088/0953-8984/25/24/245303. Epub 2013 May 24.
We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. (1)H, (13)C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp(2) carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions.
我们报告了高温纳米金刚石向洋葱状结构转变的首例核磁共振（NMR）和电子顺磁共振（EPR）研究。测量了初始纳米金刚石样品以及在 600、700、800 和 1800°C 下退火的样品的 (1)H、(13)C NMR 和 EPR 谱。对于在 600 到 800°C 下退火的样品，我们的 NMR 数据揭示了表面修饰的早期阶段，以及随着退火温度的升高，sp(2)碳含量的逐渐增加。首次记录了这些定量实验数据。这些发现与 EPR 数据相关，EPR 数据表明悬空键 EPR 线宽对空气含量的敏感性随退火温度的升高而增加，这证明了金刚石核的外部层随后的石墨化。在 1800°C 下退火的样品显示纳米金刚石颗粒完全转化为洋葱状碳。
