Engineering highly coherent shallow Nitrogen Vacancy centers with long coherence times for biosensing experiments*

Nitrogen vacancy (NV) centers are point defects in diamond that can be used to sense magnetic fields at room temperature, making them an attractive platform for nanoscale biosensing. For such experiments, NV centers need to be within a few nanometers of the target molecules. Therefore, NV centers must be close to the diamond surface, and the molecules must be immobilized above the NV center. Currently, these experiments are limited by two major issues. First, diamond surfaces host magnetic and electric noise, which degrades the coherence of shallow NV centers. Second, there are no chemical methods to functionalize the diamond surface to attach a wide range of large, fragile molecules of interest. To address these challenges, we built an ultra-high vacuum cluster tool that combines surface preparation and characterization with NV spin measurements. This highly controlled environment allows us to create pristine diamond surfaces with new surface chemistries and measure the impact on shallow NV center coherence without breaking vacuum. In addition, we explore the utility of these surface chemistries for gentle wet chemical functionalization to attach molecules to the diamond surface for nanoscale sensing applications.