Abstract
A new method is introduced to study electron transport on the mesoscopic scale. A scanning tunnelling microscope (STM) tip is used both to form a point-contact potential probe to a thin film and to affect scattering centres in its vicinity. We detect abrupt changes in the voltage with this probe as a function of both tip position and tip-sample voltage. These changes could be interpreted as due to spatial shifts of scattering centres in the film surface.