McKelvey, Kim M. (Kim Martin), Perry, David, Byers, Joshua C., Colburn, Alex W. and Unwin, Patrick R. (2014) Bias modulated scanning ion conductance microscopy. Analytical Chemistry, Volume 86 (Number 7). pp. 3639-3646. doi:10.1021/ac5003118

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Abstract

Nanopipets are versatile tools for nanoscience, particularly when used in scanning ion conductance microscopy (SICM) to determine, in a noncontact manner, the topography of a sample. We present a new method, applying an oscillating bias between a quasi-reference counter electrode (QRCE) in the SICM nanopipet probe and a second QRCE in the bulk solution, to generate a feedback signal to control the distance between the end of a nanopipet and a surface. Both the amplitude and phase of the oscillating ion current, induced by the oscillating bias and extracted using a phase-sensitive detector, are shown to be sensitive to the probe–surface distance and are used to provide stable feedback signals. The phase signal is particularly sensitive at high frequencies of the oscillating bias (up to 30 kHz herein). This development eliminates the need to physically oscillate the probe to generate an oscillating ion current feedback signal, as needed for conventional SICM modes. Moreover, bias modulation allows a feedback signal to be generated without any net ion current flow, ensuring that any polarization of the quasi reference counter electrodes, electro-osmotic effects, and perturbations of the supporting electrolyte composition are minimized. Both feedback signals, magnitude and phase, are analyzed through approach curve measurements to different surfaces at a range of distinct frequencies and via impedance measurements at different distances from a surface. The bias modulated response is readily understood via a simple equivalent circuit model. Bias modulated (BM)-SICM is compared to conventional SICM imaging through measurements of substrates with distinct topographical features and yields equivalent results. Finally, BM-SICM with both amplitude and phase feedback is used for topographical imaging of subtle etch features in a calcite crystal surface. The 2 modes yield similar results, but phase-detection opens up the prospect of faster imaging.

Item Type:	Journal Article
Divisions:	Faculty of Science > Chemistry
Journal or Publication Title:	Analytical Chemistry
Publisher:	American Chemical Society
ISSN:	0003-2700
Official Date:	11 March 2014
Dates:	Date Event 11 March 2014 Published
Volume:	Volume 86
Number:	Number 7
Page Range:	pp. 3639-3646
DOI:	10.1021/ac5003118
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access

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