Scanning ion conductance microscopy (SICM) has proven to be a powerful tool for topography measurement in aqueous solution. Recent researches further extend the application of SICM for simultaneous topography measurement and local physical property measurement, among which, surface charge measurement draws the most attention for its potential application in material science. Recent work, in particular that of our group<sup>1</sup> and of Unwin and coworkers,<sup>2</sup> has demonstrated the application of SICM in simultaneous surface charge mapping and topography measurement. Here, we describe the use of relative ion current rectification (ICR) measurements to qualitatively evaluate the surface charge in an easily interpreted manner. When a quartz nanopipette is approached close to surface, ICR through the tip is influenced by both the pipette charge and the substrate charge. Based on this property, we have developed surface charge measurements through the use of differential current-voltage curve measurement at each pixel in an image. Controlled by a commercial FPGA, SICM scanning is paused temporally at each pixel in a scan, and a current-voltage curve is collected to extract local surface charge information. Comparison of the current-voltage responses close to and far from the surface allows extraction of the contribution of the charge. We will detail the instrumental operation and present data on various samples with heterogeneous surface charge.

Simultaneous topography and qualitative surface charge mapping with scanning ion conductance microscopy

256th National Meeting (2018)

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