Impedance feedback control for scanning electrochemical microscopy

A new constant-distance imaging method based on the relationship between ti p impedance and tip-substrate separation has been developed for the scannin g electrochemical microscope. The tip impedance is monitored by application of a high-frequency ac voltage bias between the tip and auxiliary electrod e. The high-frequency ac current is easily separated from the dc-level fara daic electrochemistry with a simple RC filter, which allows impedance measu rements during feedback or generation/collection experiments. By employing a piezo-based feedback controller, we are able to maintain the impedance at a constant value and, thus, maintain a constant tip-substrate separation. Application of the method to feedback and generation/collection experiments with tip electrodes as small as 2 mum is presented.