Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy of bulk quantum materials have provided insight into phenomena, such as quantum phase criticality, magnetism, and superconductivity. With the emergence of nanoscale 2D materials with magnetic phenomena, inductively detected NMR and NQR spectroscopy are not sensitive enough to detect the smaller number of spins in nanomaterials. The nitrogen-vacancy (NV) center in diamond has shown promise in bringing the analytic power of NMR and NQR spectroscopy to the nanoscale. However, due to depth-dependent formation efficiency of the defect centers, noise from surface spins, band bending effects, and the depth dependence of the nuclear magnetic field, there is ambiguity regarding the ideal NV depth for surface NMR of statistically polarized spins. In this work, we prepared a range of shallow NV ensemble layer depths and determined the ideal NV depth by performing NMR spectroscopy on statistically polarized 19F in Fomblin oil on the diamond surface. We found that the measurement time needed to achieve a signal-to-noise ratio of 3 using XY8-N noise spectroscopy has a minimum at an NV ensemble depth of 5.5 ± 1.5 nm for ensembles activated from 100 ppm nitrogen concentration. To demonstrate the sensing capabilities of NV ensembles, we perform NQR spectroscopy on the 11B of hexagonal boron nitride flakes. We compare our best diamond to previous work with a single NV and find that this ensemble provides a shorter measurement time with excitation diameters as small as 4 μm. This analysis provides ideal conditions for further experiments involving NMR/NQR spectroscopy of 2D materials with magnetic properties.

中文翻译：

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使用钻石中深度优化的氮空位系综的纳米级固态核四极共振光谱

体量子材料的核磁共振 (NMR) 和核四极共振 (NQR) 光谱提供了对量子相临界、磁性和超导性等现象的深入了解。随着具有磁性现象的纳米级二维材料的出现，感应检测的 NMR 和 NQR 光谱不够灵敏，无法检测纳米材料中较小数量的自旋。金刚石中的氮空位 (NV) 中心显示出有望将 NMR 和 NQR 光谱的分析能力提升到纳米尺度。然而，由于缺陷中心的深度依赖形成效率、表面自旋噪声、带弯曲效应和核磁场的深度依赖性，统计极化自旋的表面 NMR 的理想 NV 深度存在歧义。在这项工作中，我们准备了一系列浅 NV 系综层深度，并通过对钻石表面 Fomblin 油中统计极化的 19F 进行 NMR 光谱分析来确定理想的 NV 深度。我们发现，对于从 100 ppm 氮浓度激活的集合，使用 XY8-N 噪声光谱实现 3 的信噪比所需的测量时间在 5.5 ± 1.5 nm 的 NV 集合深度处具有最小值。为了展示 NV 系综的传感能力，我们对六方氮化硼薄片的 11B 进行了 NQR 光谱分析。我们将我们最好的金刚石与之前使用单个 NV 的工作进行比较，发现这个整体提供更短的测量时间，激发直径小至 4 μm。该分析为涉及具有磁性的二维材料的 NMR/NQR 光谱的进一步实验提供了理想条件。