Impedance Feedback Control for Scanning Electrochemical Microscopy

Abstract

A new constant-distance imaging method based on the relationship between tip impedance and tip-substrate separation has been developed for the scanning electrochemical microscope. The tip impedance is monitored by application of a high-frequency ac voltage bias between the tip and auxiliary electrode. The high-frequency ac current is easily separated from the dc-level faradaic electrochemistry with a simple RC filter, which allows impedance measurements 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 microm is presented.

Spatial Imaging of Cu2+‐Ion Release by Combining Alternating Current and Underpotential Stripping Mode Scanning Electrochemical Microscopy

“…The visualization of corroding sites was done using feedback mode SECM in the presence of redox mediators [16 -19] or substrategeneration-tip-collection mode SECM measuring the fluxes of dissolved Fe 2þ ions [20]. Alternating current was used before in SECM as a tool to control the tip-to-sample distance in electrolyte solutions of high ionic strength [21,22]. Recently, alternating current mode SECM (AC-SECM) was applied for the visualization of local variations in electrochemical surface activity [23 -29].…”

Constant‐Distance Mode Scanning Electrochemical Microscopy. Part II: High‐Resolution SECM Imaging Employing Pt Nanoelectrodes as Miniaturized Scanning Probes

“…The response of the tuning fork/SECM-tip assembly was used as a measure of shear-force induced damping of the tip vibration thus enabling a feedback control of tip-to-sample separation [22,23]. Furthermore, an electrochemical impedance method for controlling the tip-to-sample distance during SECM experiments was proposed [24] and the integration of SECM into atomic force microscopes (AFM) by using specially-designed AFM cantilevers acting simultaneously as a force sensor for topographical AFM imaging and an ultramicroelectrode for electrochemical SECM imaging could be successfully demonstrated [26 ± 32].…”

Development of High-Resolution Scanning Electrochemical Microscopy for Nanoscale Topography and Electrochemical Simultaneous Imaging

“…Specifically, topography-related artifacts in these images can be avoided by employing probe-sample distance control. Various feedback distance control systems have been developed, including those based on atomic force microscopy, 15,16 shear force, [17][18][19] impedance, [20][21][22] faradaic current, 20,23 ion current, 11,12,24 and electrochemical signals. [25][26][27] Impedance-feedback and constantcurrent distance control systems are effective because additional modification of the probe for distance control is not required.…”