高温退火增强金刚石13 C超极化
High temperature annealing enhanced diamond 13C hyperpolarization at room temperature
摘要：
光学动态核极化（DNP）方法为核自旋的可消除超极化打开了大门，将它们的NMR/MRI特征提高了几个数量级。富含带负电荷的氮空位（NV）缺陷中心的纳米金刚石粉末最近已经成为这样一种有前景的平台，其中13 C核可以在室温和低磁场下完全通过光泵浦缺陷超极化。考虑到将这种13 C极化传递到外部液体中的核的令人信服的可能性，迫切需要工程生产高度“超极化”的金刚石颗粒。在本文中，我们报告的各种材料尺寸影响光学13 C超极化金刚石颗粒的系统研究-特别是电子辐照和退火条件，驱动NV中心的形成。我们惊讶地发现，在接近1720 ℃的高温下进行金刚石退火对超极化水平有显著的影响，使其比通过常规方法退火的材料提高高达36倍。我们解开了这些收益的有趣的材料起源，并证明它们产生于NV电子弛豫时间和相干时间的同时改善，以及顺磁含量的减少，和13 C弛豫寿命的增加。总的来说，这表明由于高温退火，金刚石晶格从辐射损伤中显著恢复。我们的工作提出了荧光，13 C超极化，纳米金刚石和路径的指导材料生产的方法，用于其作为多模态（光学和MRI）成像和超极化剂。
英文摘要：
Methods of optical dynamic nuclear polarization (DNP) open the door to the replenishable hyperpolarization of nuclear spins, boosting their NMR/MRI signature by orders of magnitude. Nanodiamond powder rich in negatively charged Nitrogen Vacancy (NV) defect centers has recently emerged as one such promising platform, wherein 13C nuclei can be hyperpolarized through the optically pumped defects completely at room temperature and at low magnetic fields. Given the compelling possibility of relaying this 13C polarization to nuclei in external liquids, there is an urgent need for the engineered production of highly "hyperpolarizable" diamond particles. In this paper, we report on a systematic study of various material dimensions affecting optical 13C hyperpolarization in diamond particles -- especially electron irradiation and annealing conditions that drive NV center formation. We discover surprisingly that diamond annealing at elevated temperatures close to 1720C have remarkable effects on the hyperpolarization levels, enhancing them by upto 36-fold over materials annealed through conventional means. We unravel the intriguing material origins of these gains, and demonstrate they arise from a simultaneous improvement in NV electron relaxation time and coherence time, as well as the reduction of paramagnetic content, and an increase in 13C relaxation lifetimes. Overall this points to significant recovery of the diamond lattice from radiation damage as a result of the high-temperature annealing. Our work suggests methods for the guided materials production of fluorescent, 13C hyperpolarized, nanodiamonds and pathways for their use as multi-modal (optical and MRI) imaging and hyperpolarization agents.
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