Fabrication of tips for scanning probe magnetometry by diamond growth

The use of quantum sensors is promising detailed insights into physical phenomena such as magnetism or superconductivity. One example of such quantum sensors is a microscopic diamond tip containing nitrogen vacancy (NV) centers, which is capable of producing correlated measurements of vectorial magnetic fields and the sample topography on the nanoscale. In this study, we present a chemical vapor deposition (CVD) process to produce diamond tips with NV centers by overgrowing microstructured diamond substrates. The resulting diamond tips exhibit a radius of curvature of approximately 10 nm, suitable for use as a probe in an atomic force microscope (AFM). The magnetic sensitivity of the CVD-grown diamond tips is characterized with pulsed measurements of the optically detected magnetic resonance (ODMR), which yield a minimum magnetic sensitivity of 60 µT/√Hz. The growth of the diamond microstructures is observed to differ from the commonly used geometric model predicting CVD growth of bulk diamond crystals. We identify an empirical model for the growth behavior of the microstructures by taking into account processes described in the step flow growth model for crystals. Additionally, we demonstrate the applicability of the developed CVD growth process to membrane substrates required for the preparation of magnetometry-capable diamond tips.