▎ 摘　　要

The application of imaging techniques based on ensembles of nitrogen-vacancy (N-V) sensors in diamond to characterize electrical devices has been proposed, but the compatibility of N-V sensing with operational gated devices remains largely unexplored. Here we report the fabrication of graphene field-effect transistors directly on the diamond surface and their characterization by N-V microscopy. The current density within the gated graphene is reconstructed from N-V-magnetometry measurements under both mostly p-and n-type doping, but the exact doping level is found to be affected by the measurements. Additionally, we observe a surprisingly large modulation of the electric field at the diamond surface under an applied gate potential, seen in N-V-photoluminescence and N-V-electrometry measurements, suggesting a complex electrostatic response of the oxide-graphene-diamond structure. Possible solutions to mitigate these effects are discussed.