Fig. 1: Crystal and defect structure, schematic for the device, STM topography and spectroscopy, photoluminescence at tip-sample junction.

a Crystal structure of diamond, consisting of C atoms (red), along with an NV center, consisting of a N substitution (blue) for C and a neighboring C vacancy (green); NV centers in diamond are oriented along the [111] direction. b Schematic of measurement geometry. Monolayer graphene is transferred onto diamond (100) single crystals and the graphene/diamond structure is clamped down by a Mo plate. Bias voltage is applied through the Mo clamp with tunneling current measurement by an uncoated or Au-coated tungsten STM tip. c STM topography of graphene on diamond showing characteristic honeycomb lattice (V_Bias = -500 mV, I_Setpoint = 70 pA). d Large energy-range dI/dV spectrum showing 5.5 eV diamond band gap from -3.2 to +2.3 eV (V_Bias = -5.00 V, I_Setpoint = 70 pA). Inset shows smaller-scale spectrum with expected V-shape from graphene (V_Bias = -500 mV, I_Setpoint = 70 pA). e Photoluminescence from sample in 5 \(\mu\) m diameter laser spot surrounding tip-sample junction (532 nm excitation with 75 \(\mu\) W power, 12s integration, T = 77 K). The expected photoluminescence from NV^- centers, including the characteristic 637 nm zero-phonon line (shaded in red) can be seen clearly, indicating the presence of NV^- centers in our STM field-of-view. The inset is a camera view of the tip-sample junction with the 532 nm laser focused on the tip apex.