  The ability to perform nanoscale electric field imaging of elementary charges
at ambient temperatures will have diverse interdisciplinary applications. While
the nitrogen-vacancy (NV) center in diamond is capable of high-sensitivity
electrometry, demonstrations have so far been limited to macroscopic field
features or detection of single charges internal to diamond itself. In this
work we greatly extend these capabilities by using a shallow NV center to image
the electric field of a charged atomic force microscope tip with nanoscale
resolution. This is achieved by measuring Stark shifts in the NV spin-resonance
due to AC electric fields. To achieve this feat we employ for the first time,
the integration of Qdyne with scanning quantum microscopy. We demonstrate near
single charge sensitivity of $\eta_e = 5.3$ charges/$\sqrt{\text{Hz}}$, and
sub-charge detection ($0.68e$). This proof-of-concept experiment provides the
motivation for further sensing and imaging of electric fields using NV centers
in diamond.
