Diamond Surfaces\nwith Lateral Gradients for Systematic\nOptimization of Surface Chemistry for Relaxometry – a Low-Pressure\nPlasma-Based Approach

Diamond is increasingly popular because of its unique\nmaterial\nproperties. Diamond defects called nitrogen vacancy (NV) centers allow\nfor measurements with unprecedented sensitivity. However, to achieve\nideal sensing performance, NV centers need to be within nanometers\nfrom the surface and are thus strongly dependent on the local surface\nchemistry. Several attempts have been made to compare diamond surfaces.\nHowever, due to the high price of diamond crystals with shallow NV\ncenters, a limited number of chemical modifications have been studied.\nHere, we developed a systematic method to investigate the continuity\nof different local environments with varying densities and natures\nof surface groups in a single experiment on a single diamond plate.\nTo achieve this goal, we used diamonds with a shallow ensemble of\nNV centers and introduced a chemical gradient across the surface.\nMore specifically, we used air and hydrogen plasma. The gradients\nwere formed by a low-pressure plasma treatment after masking with\na right-angled triangular prism shield. As a result, the surface contained\ngradually more oxygen/hydrogen toward the open end of the shield.\nWe then performed wide-field relaxometry to determine the effect of\nsurface chemistry on the sensing performance. As expected, relaxation\ntimes and thus sensing performance indeed vary along the gradient.