Carbon tips as sensitive detectors for nanoscale surface and sub-surface charge

Electrically insulating tips prepared by carbon deposition are used as sensitive detectors of nanoscale charge patterns on cleaved insulating surfaces. Dynamic scanning force microscopy images recorded with a neutral carbon tip reveal the surface topography and strong local charging at step edges while images taken with a charged tip exhibit subtle contrast features resulting from charges located at or beneath the surface of flat terraces. Analysing dynamic phenomena during imaging allows a determination of charge polarity and identifies sub-surface charges as trapping centres for charges exchanged between the tip and the surface. A density of a few hundred charged sub-surface defects per μm 2 is determined on while the defect density is one order of magnitude smaller on CaF 2 (111). The method allows the detection of elementary charges at room temperature.