金刚石中氮空位层形成方法的比较
Comparison of different methods of nitrogen-vacancy layer formation in diamond for widefield quantum microscopy
摘要：
金刚石衬底近表面氮空位（NV）缺陷薄层是基于NV的宽场磁显微镜的主要研究对象，在物理学、地质学和生物学等领域有着广泛的应用。存在几种方法来产生这种NV层，其通常涉及通过生长和/或照射将氮原子（N）和空位（V）结合到金刚石中。虽然已经有详细的研究个别方法，直接并排实验比较所产生的磁灵敏度仍然缺失。在这里，我们描述了在室温和低温下，通过三种不同的方法制备的$\approx100$ nm厚的NV层：1）富N高压高温（HPHT）金刚石的低能碳照射，2）$δ$掺杂的化学气相沉积（CVD）金刚石的碳照射，3）低能N $^+$或CN $^-$注入到无N CVD金刚石中。尽管每种方法之间存在显著差异，但我们发现最好的HPHT样品产生相似的磁灵敏度（平均在2倍以内），对于直流磁场，$δ$ ~ $μ$ T Hz $^{-1/2}$，对于交流磁场，$<100$ ~nT Hz $^{-1/2}$（对于$400$ ~nm~ $\times~400$ ~nm像素），而N $^+$和CN $^-$注入的样品表现出差2-5倍的灵敏度，在室温和低温下。我们还研究了各自的方法所造成的晶格应变，并讨论了宽场NV成像的影响。每种方法的优点和缺点，以及未来可能的改进，进行了讨论。这项研究强调，低能量辐照的HPHT金刚石，尽管其相对简单，成本低，是一种有竞争力的方法，以创建薄NV层的宽场磁成像。
英文摘要：
Thin layers of near-surface nitrogen-vacancy (NV) defects in diamond substrates are the workhorse of NV-based widefield magnetic microscopy, which has applications in physics, geology and biology. Several methods exist to create such NV layers, which generally involve incorporating nitrogen atoms (N) and vacancies (V) into the diamond through growth and/or irradiation. While there have been detailed studies of individual methods, a direct side-by-side experimental comparison of the resulting magnetic sensitivities is still missing. Here we characterise, at room and cryogenic temperatures, $\approx100$ nm thick NV layers fabricated via three different methods: 1) low-energy carbon irradiation of N-rich high-pressure high-temperature (HPHT) diamond, 2) carbon irradiation of $δ$-doped chemical vapour deposition (CVD) diamond, 3) low-energy N$^+$ or CN$^-$ implantation into N-free CVD diamond. Despite significant variability within each method, we find that the best HPHT samples yield similar magnetic sensitivities (within a factor 2 on average) to our $δ$-doped samples, of $<2$~$μ$T Hz$^{-1/2}$ for DC magnetic fields and $<100$~nT Hz$^{-1/2}$ for AC fields (for a $400$~nm~$\times~400$~nm pixel), while the N$^+$ and CN$^-$ implanted samples exhibit an inferior sensitivity by a factor 2-5, at both room and low temperature. We also examine the crystal lattice strain caused by the respective methods and discuss the implications this has for widefield NV imaging. The pros and cons of each method, and potential future improvements, are discussed. This study highlights that low-energy irradiation of HPHT diamond, despite its relative simplicity and low cost, is a competitive method to create thin NV layers for widefield magnetic imaging.
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