Scanning Electrochemical Microscopy. 15. Improvements in Imaging via Tip-Position Modulation and Lock-in Detection

The use of mai l amplitude tipposition modulation (TPM) in combination with lock-in detection of the modulated current signal greatly improves the sendtivity and image resolution of the scanning electrochemical microscope and provides a method of distinguishing between conductive and insulating areas on the substrate surface being examined. The experimental in-phase current versus distance behavior is characterized for insulating and conducting surfaces for various modulation amplitudes and frequencies. A simple derivative model of the dc response is adequate to derive the in-phase TPM response at conductorq the insulator response does not conform to the theory and is, in fact, more sendtive than predicted. Demonstration images of an interdigitated array electrode using the dc and in-phase TPM signal are compared. The in-phase TPM image is found to be superior for imaging because of its improved sendtivlty to insulating surfaces and its bipolar response over Insulators and conductors.