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 mum(2) is determined on CaCO3 (10 (1) over bar4) while the defect density is one order of magnitude smaller on CaF2 (111). The method allows the detection of elementary charges at room temperature.