The Kelvin Probe module
is an add-on module to either the OC4-Station or the full Nanonis Control System (with OC4) and is intended for the mapping of surface charge distribution or contact potential difference (CPD) between tip and sample. Its fully digital implementation allows for maximum flexibility. Any channel can for instance be selected as input signal for either amplitude or frequency shift modulation modes. An internal lock-in demodulates the input signal and a PI loop regulates the bias voltage to compensate for the change in contact potential. The modulating AC-component of the bias voltage, defined by the user, is internally added to the regulated DC bias voltage.