an electrode potential and or current control coarse control of the secm tip b a pt disk ume which is typically mounted perpendicular to the substrate surface 52 but can be mounted at different angles is realised by a three dimensional manual x y z stage controlled by manipulator screws 56 note that other means of achieving this positioning are also possible fine control is realised by three x y z piezoelectric positioners 42 fitted with strain gauge sensors the piezoelectric positioners 42 operated in closed loop are controlled by an amplifier servo 47 the piezoelectric positioner amplifier servo is controlled by a personal computer 45 an ac signal provided by an ac generator 49 is added to the z piezoelectric positioner control by a signal adder 48 the ac signal creates a sinusoidal oscillation of in the height of the secm tip b about the average tip height but other oscillation profiles can be used the computer 45 includes processing means comprising one or more processors memory means comprising one or more memories and a computer program stored in the memory means the processing means under control of the computer program performs various actions that are described below including measuring detecting and controlling operations embodiments of the invention are typically implemented in a faraday cage 41 on a vibration isolation table 55 in a two electrode arrangement with the metal wire a or ume tip b as the working or active electrode and a quasi reference electrode.