We utilize an ac feedback signal to control the size of Cu nanogaps by electrochemically depositing or dissolving copper onto pre-pattemed electrodes. The ac frequency in this work was set to 820 Hz, at which the capacitive reactance contributes notably to the gap impedance. As a result, distinct changes can be observed in the monitored signals at relatively large gap size, as compared with the high sensitivity of resistive reactance to small gap distance when the frequency is set lower. Within the present parameter, we have prepared nanoscale gaps ranging from tens of nm to sub-10 nm by carefully choosing the subsequent deposition or dissolution time. (c) 2006 Elsevier Ltd. All rights reserved.