Abstract
Surface termination of semiconductors is important for their applications in electronics because it governs electrical properties at interfaces. For quantum sensors and qubits based on spins in solids, this is crucial when they are located a few nanometers below the crystal surface. In the case of diamond, oxygen termination is preferential for quantum sensing with nitrogen-vacancy (NV) centers. Here, we present local surface modification of a nonconductive diamond surface utilizing conductive atomic force microscopy under laser illumination. By applying this method, we demonstrate not only a removal of fluorescence background but also control over the charge state of single NV centers. The latter show an improvement of the optically detected magnetic resonance contrast from 1% up to 29% after the treatment. We assume that local surface oxidation is happening on the diamond, which has already been demonstrated for conducting hydrogenated surfaces, but its implementation to nonconductive surfaces remains challenging.