Substitutional nitrogen impurities within the diamond lattice, known as P1 centers, have unpaired electrons that can mediate microwave driven dynamic nuclear polarization (DNP). In this paper we explore DNP of the bulk ¹³C spins in micrometer-sized P1 diamond particles and demonstrate a 550-fold DNP enhancement of the bulk ¹³C spins at room temperature in a 9 T magnetic field or 250 GHz for g ≈ 2 electrons. We study the DNP mechanisms, exploring their dependence on sample spinning frequency and microwave irradiation frequency using both continuous wave and frequency swept microwave irradiation, and discuss the results alongside recent DNP studies in the literature. Even with a modest microwave irradiation power of 160 mW from our frequency swept solid-state microwave source, we achieve a significant ¹³C signal enhancement, ε = 270 at room temperature. The enhancements were found to increase with the magic angle spinning (MAS) frequency, ω_r/2π, and the results provide mechanistic insights into how different electron populations contribute to the observed DNP efficiency. These findings are inherently interesting and of practical importance in view of the recently reported diamond rotors fabricated from P1 high-pressure, high-temperature (HPHT) diamond.

中文翻译：

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金刚石中具有 P1 中心的动态核极化


金刚石晶格内的取代氮杂质（称为 P1 色心）具有不成对的电子，可以介导微波驱动的动态核极化 （DNP）。在本文中，我们探讨了微米级 P1 金刚石颗粒中体体 ¹³C 自旋的 DNP，并展示了在室温下，在 9 T 磁场或 250 GHz 磁场中，g ≈ 2 个电子的体体 ¹³C 自旋的 DNP 增强了 550 倍。我们研究了 DNP 机制，使用连续波和频率扫描微波照射探索它们对样品旋转频率和微波照射频率的依赖性，并将结果与文献中最近的 DNP 研究一起讨论。即使我们的频率扫描固态微波源具有 160 mW 的适度微波照射功率，我们也实现了显著的 ¹³C 信号增强，在室温下ε = 270。发现增强功能随着魔角旋转 （MAS） 频率 ω_r/2π 的增加而增加，并且结果为不同电子群如何对观察到的 DNP 效率做出贡献提供了机制见解。鉴于最近报道的由 P1 高压高温 （HPHT） 金刚石制成的金刚石转子，这些发现本身就很有趣，具有实际意义。