A scanning force microscope (SFM) has been extended by an a.c. circuit, which measures the current between a metallized tip and the excited sample. Using the lock-in principle, the resulting current amplitude and phase shift information can be visualized by the image processing unit of the SFM. Like in scanning tunnelling microscopy, it is possible to achieve atomic resolution on highly oriented pyrolytic graphite (HOPG). Experiments were performed with four different samples: a carbon fibre embedded in poly(phenylene sulfide) matrix and pulled out, carbon fibres with two different plasma treatment times and an untreated reference fibre. A grey-scale threshold analysing procedure is discussed to evaluate the amount of bare and covered fibre surface.