Integrated Scanning Kelvin Probe-Scanning Electrochemical Microscope System: Development and First Applications

The integration of a scanning Kelvin probe (SKP) and a scanning electrochemical microscope (SECM) into a single SKP-SECM setup, the concept of the proposed system, its technical realization, and first applications are presented and discussed in detail. A preloaded piezo actuator placed in a grounded stainless steel case was used as the driving mechanism for oscillation of a Pt disk electrode as conventionally used in SECM when the system was operated in the SKP mode. Thus, the same tip is recording the contact potential difference (CPD) during SKP scanning and is used as a working electrode for SECM imaging in the redox-competition mode (RC-SECM). The detection of the local CPD is established by amplification of the displacement current at an ultralow noise operational amplifier and its compensation by application of a variable backing potential (V(b)) in the external circuit. The control of the tip-to-sample distance is performed by applying an additional alternating voltage with a much lower frequency than the oscillation frequency of the Kelvin probe. The main advantage of the SKP-SECM system is that it allows constant distance measurements of the CPD in air under ambient conditions and in the redox-competition mode of the SECM in the electrolyte of choice over the same sample area without replacement of the sample or exchange of the working electrode. The performance of the system was evaluated using a test sample made by sputtering thin Pt and W films on an oxidized silicon wafer. The obtained values of the CPD correlate well with known data, and the electrochemical activity for oxygen reduction is as expected higher over Pt than W.