3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.
Institute for Quantum Optics, University of Ulm , 89081 Ulm, Germany.
Nano Lett. 2016 Apr 13;16(4):2228-33. doi: 10.1021/acs.nanolett.5b04511. Epub 2016 Mar 4.
The negatively charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution. This provides insights into the efficiency of vacancy diffusion and recombination paths concurrent to the formation of NV centers. It was found that the range of efficient formation of NV centers is limited only to approximately 10 to 15 nm (radius) around the initial ion track of irradiating helium atoms. Using this information we demonstrate the fabrication of nanometric-thin (δ) profiles of NV centers for sensing external spins at the diamond surface based on a three-step approach, which comprises (i) nitrogen-doped epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy helium irradiation and thermal annealing, and (iii) controlled layer thinning by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to 50 μs are demonstrated at depths of less than 5 nm in material with 1.1% of (13)C (depth estimated by spin relaxation (T1) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.
最近，金刚石中的带负电的氮空位（NV）中心已被证明是外部自旋的绝佳传感器。然而，要对近表面区域中的 NV 中心进行最佳工程设计，仍需要定量了解在热退火过程中通过空位捕获对其进行激活的情况。为此，我们报告了通过具有纳米分辨率的分步蚀刻对近表面氦离子诱导 NV 中心（和相关氦缺陷）的深度分布进行的研究。这提供了有关 NV 中心形成过程中同时发生的空位扩散和复合途径的效率的深入了解。结果发现，NV 中心的有效形成范围仅局限于辐照氦原子的初始离子轨迹周围约 10 到 15nm（半径）的范围内。利用这些信息，我们基于三步法演示了在金刚石表面上用于感测外部自旋的纳米级（δ）NV 中心的制造，该方法包括（i）氮掺杂外延 CVD 金刚石外延生长，（ii）低能氦离子辐照和热退火激活 NV 中心，以及（iii）通过低损伤等离子体刻蚀进行受控的层减薄。在深度小于 5nm 的材料中（通过自旋弛豫（T1）测量估计的深度），深度小于 5nm 时，演示了自旋相干时间（Hahn 回波）长达 50μs。最后，还实验研究了高离子通量下氦离子辐照技术的局限性。
