First principles of hot-tip scanning electrochemical microscopy: Differentiating substrates according to their thermal conductivities

The use of ac polarized microelectrodes in the arrangement for scanning electrochemical microscopy is described. Application of a high frequency ac waveform to a microelectrode tip results in a resistive heating of the surrounding electrolyte solution and the onset of the electrothermal flow. We report that the presence of a substrate in close proximity to the hot tip leads to a substantial change of the temperature in the hot zone, which in turn results in a measurable effect on the shape of the recorded approach curves. Thus, the observed changes in the faradaic current, measured with the tip, can be used to distinguish substrates according to their thermophysical properties, namely, thermal conductivity. Experimental data are shown to be in good agreement with the results of the theoretical simulations. This work exemplifies initial findings obtained with a novel technique that is termed Hot-Tip Scanning Electrochemical Microscopy (HT-SECM).