Ong S Y, Chipaux M, Nagl A, Schirhagl R
Groningen University, University Medical Center Groningen, Antonius Deusinglaan 1, 9713 Groningen, The Netherlands.
Phys Chem Chem Phys. 2017 May 3;19(17):10748-10752. doi: 10.1039/c6cp07431f.
Nanodiamonds with dimensions down to a few tens of nanometers containing nitrogen-vacancy (NV) color centers have revealed their potential as powerful and versatile quantum sensors with a unique combination of spatial resolution and sensitivity. The NV centers allow transducing physical properties, such as strain, temperature, and electric or magnetic field, to an optical transition that can be detected in the single photon range. For example, this makes it possible to sense a single electron spin or a few nuclear spins by detecting their magnetic resonance. The location and orientation of these defects with respect to the diamond surface play a crucial role in interpreting the data and predicting their sensitivities. Despite its relevance, the geometry of these nanodiamonds has never been thoroughly investigated. Without accurate data, spherical models have been applied to interpret or predict results in the past. With the use of High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), we investigated nanodiamonds with an average hydrodynamic diameter of 25 nm (the most common type for quantum sensing) and found a flake-like geometry, with 23.2 nm and 4.5 nm being the average lateral and vertical dimensions. We have also found evidence for a preferred crystallographic orientation of the main facet in the (110) direction. Furthermore, we discuss the consequences of this difference in geometry on diamond-based applications. Shape not only influences the creation efficiency of nitrogen-vacancy centers and their quantum coherence properties (and thus sensing performance), but also the optical properties of the nanodiamonds, their interaction with living cells, and their surface chemistry.
尺寸低至几十纳米且含有氮空位（NV）色心的纳米金刚石，已展现出其作为强大且通用的量子传感器的潜力，具备空间分辨率和灵敏度的独特组合。NV色心可将诸如应变、温度以及电场或磁场等物理性质转换为可在单光子范围内检测到的光学跃迁。例如，通过检测单个电子自旋或少数核自旋的磁共振，就能够实现对它们的探测。这些缺陷相对于金刚石表面的位置和取向在解释数据以及预测其灵敏度方面起着至关重要的作用。尽管其具有相关性，但这些纳米金刚石的几何形状从未得到过彻底研究。在缺乏准确数据的情况下，过去一直应用球形模型来解释或预测结果。通过使用高分辨率透射电子显微镜（HR-TEM）、扫描电子显微镜（SEM）和原子力显微镜（AFM），我们研究了平均流体动力学直径为25纳米的纳米金刚石（量子传感中最常见的类型），发现其具有片状几何形状，平均横向尺寸和纵向尺寸分别为23.2纳米和4.5纳米。我们还发现了主晶面在（110）方向上存在择优晶体取向的证据。此外，我们讨论了这种几何形状差异对基于金刚石的应用所产生的影响。形状不仅会影响氮空位中心的产生效率及其量子相干特性（进而影响传感性能），还会影响纳米金刚石的光学性质、它们与活细胞的相互作用以及它们的表面化学性质。
