Bias Modulated Scanning Ion Conductance
Microscopy
David Perrya,b, Kim KcKelveyb, Sophie Kinnearb, Dmitry Momotenkob, Joshua Byersb and Patrick Unwinb
a) MOAC DTC b) Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, Warwickshire
Introduction
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Scanning Ion Conductance Microscopy is a powerful non contact, solution phase,
imaging technique1
Uses ion conductance current between electrode in nanopipette and one in bulk
solution (right) to map interfacial properties, typically topography
Requires robust feedback loop to maintain tip-substrate distance, typically achieved
through modulating tip position2
Through oscillating the bias between the electrodes, we achieve a robust feedback
and a response3, sensitive for mapping topography and surface charge
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Response
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The response in the amplitude and phase
components of the AC signal is explored, upon
approaching a glass substrate (left)
A measurable response is observed at high
oscillation frequencies, allowing a faster
response and scanning than conventional SICM
Also see that in lower electrolyte concentrations,
response is sensitive to double layer charge
Z/μm
Topography
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X/μm
Y/μm
Capabilities of Bias Modulated
SICM for mapping topography are
shown using a polystyrene film
with glass pinholes (left) and an
etched calcite substrate (right)
Topography was shown to match
AFM data and conventional
distance modulated SICM scans
Y/μm
Z/μm
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X/μm
Surface Charge
X/μm
Relative
AC
Y/μm
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Y/μm
Through oscillating the bias about a
non-zero potential, the technique
becomes sensitive to the surface
charge
This allows us to generate charge
maps demonstrated here for the
polystyrene glass substrate, using the
phase (center) and amplitude (right)
to show differently charged regions
Y/μm
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Minimum
Phase/°
Z/μm
X/μm
X/μm
Conclusions
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A large feedback signal can be measured using bias modulated SICM up to very high frequencies allowing a faster response for
faster scanning
Avoids electro-osmotic flow effects through performing the oscillation about 0V
Response is sensitive to the surface in both the amplitude and phase of the AC signal
Can use bias modulated SICM to accurately map surface topography
Can be used as a very powerful tool for charge mapping, as the technique is sensitive in the ionic current, AC amplitude and
phase to double layer effects
References
(1) Hansma, P. K.; Drake, B.; Marti, O.; Gould, S. A. C.; Prater, C. B. Science 1989, 243, 641–643.
(2) Chen, C.; Zhou, Y.; Baker, L. A. Ann. Rev. Anal. Chem. 2012, 5, 207–228.
(3) McKelvey, K.; Perry, D.; Byers, J. C.; Colburn, A. W.; Unwin, P. R. Anal. Chem, 2014, 86, 3639−3646.