Development of multi-dimensional methods for scanning electrochemical microscopy (SECM)

This dissertation focuses on the development of instrumentation for scanning electrochemical microscopy (SECM) to expand the imaging possibilities of the technique. This work includes the implementation of constant distance imaging and integration of stripping voltammetry and SECM.; Constant distance SECM involves the implementation of a closed-loop control that moves the tip to correct for deviations from the desired separation. Thus, collection of tip-current data is done while independently controlling the tip-sample separation. This prevents tip damage and provides additional sample topographic information. Anodic stripping voltammetry (ASV) enables the simultaneous detection of multiple species from one imaging experiment.; Two different constant distance techniques are studied: shear force and impedance mode. Shear force control has been used for constant distance imaging in near field scanning optical microscopy. Shear force detection in SECM was achieved with tips made of carbon fiber electrodes attached to quartz tuning forks. These specially built tips were time consuming to fabricate, fragile, and difficult to handle.; The difficulties in shear force detection motivated the development of a new constant distance approach: the impedance mode. Tip impedance is a function of tip-sample separation and is used to maintain constant distance during imaging experiments. Changes in tip impedance as it approaches a substrate are followed by multiplexing an additional high frequency current to the tip. Applications of the method to feedback and generation/collection SECM modes have been demonstrated. This method uses sturdy glass-built electrodes traditionally used for SECM.; Stripping voltammetry methods have been combined with SECM to generate images of different species. A voltammogram is collected in each ( x,y) point of the image grid (pixel) at fast potential scans (100 V/s). Hg-covered Pt tip electrodes are used for stripping voltammetry - SECM. In anodic stripping voltammetry metal ions are detected by plotting the oxidation (stripping) peak currents of the voltammograms obtained during an imaging experiment. This allowed simultaneous imaging of Pb2+ and Cd 2+ down to micro-molar levels. Cathodic stripping voltammetry - SECM has been used to detect localized Cl- ions generated in situ. Chloride preconcentration and stripping was achieved during the anodic and cathodic parts of the voltammograms.