Fig. 2: STM characterization and energy level distribution of diamond defects.

a STM topography (V_Bias = -500 mV, I_Setpoint = 100 pA) of a potential NV^- defect, labeled Defect 1. b Topography from the same area as in a at a positive bias (V_Bias = +1.60 V, I_Setpoint = 70 pA) showing no feature from Defect 1, indicating that the defect is likely located subsurface, in the diamond crystal below the graphene monolayer. c dI/dV spectra (V_Bias = -900 mV, I_Setpoint = 100 pA) on and away from Defect 1, at the positions marked by the blue circle and red dot shown in a and b. d, e Energy level diagrams for NV^- and P1 defects in diamond, showing the expected position of the defect states relative to the diamond valence and conduction bands (from Ref.^35,36,37,38), as well as the position of the band edges relative to the Fermi energy E_Fermi (from Fig. 1d). f Histogram of dI/dV peak energies from measurements of 45+ defects on two different diamond samples by STM. The energies fall into two primary regions. One is centered at approximately -260 meV and the other is centered at +600 meV relative to E_Fermi. These two peak energies closely match previously reported energy levels of the NV^- ground state^35,36 (marked |g > , with excited state marked |e > ) and the P1 center^37,38 (N atom substitution for a C atom) in diamond, respectively. The valence and conduction band positions relative to E_Fermi are also shown with sky-blue and green shades. g dI/dV spectrum on a representative P1 center (V_Bias = -1.40 V, I_Setpoint = 70 pA). Inset shows topography of the P1 defect (V_Bias = +1.00 V, I_Setpoint = 70 pA). h, dI/dV spectrum on a representative NV^- defect (V_Bias = -800 mV, I_Setpoint = 100 pA). Inset shows a topography of the NV^- defect (V_Bias = -1.00 V, I_Setpoint = 70 pA). All scale bars in this figure correspond to 0.5 nm.