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electrochemical imaging


The ability to visualise surfaces and interfaces is of critical importance to understaning the dynamic processes that occur at these interfaces and in understanding to complex interactions involved.

The versatility of the techniques are vast and versatile in the systems that can be immaged. Historically scanning probe techniques have been limited to determining the surface topography, however recent advances now mean researchers can simultainiously determin many other surface characteristics at the same time.

In the Electrochemistry and Interfaces group at Warwick, we have developed several imaging methods here ourselves in order to image the systems we study. We have available many techniques for the fabrication and characterisation of new probes.

Laser pullingFIBCarbonFilling

Top: Laser Pulling of Glass Pipettes

Middle: Focused Ion Beam milling of tip geometry

Bottom: Carbon Filling of Glass Pipettes

Bias Modulated Scanning Ion Conductance Microscopy (SICM)

Scanning ion conductance microscopy (SICM) is regularly used to determine, in a noncontact manner, the topography of a sample.

We have developed a new method Bias Modulated scanning Ion Conductance Microscopy (BM-SICM) which, by oscillating the applied bias between the SICM nanopipet probe and the reference electrode in the bulk solution generates a feedback signal to control the distance between the end of a nanopipet and a surface.

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 and phase-detection opens up the mode to the prospect of faster imaging.

Bias Modulated Scanning Ion Conductance Microscopy
K. McKelvey, D. Perry, J. C. Byers, A. W. Colburn, and P. R. Unwin, Anal. Chem., 2014, 86 (7), 3639–3646


 Bias SICM examplesBias modulated (BM)-SICM is compared to conventional SICM imaging through measurements of substrates with distinct topographical features and yields equivalent results (A and B). Finally, BM-SICM with both amplitude and phase feedback is used for topographical imaging of subtle etch features in a calcite crystal surface(C and D) compared to an SEM immage (E).

Scanning Electrochemical Cell Microscopy (SECCM)

This technique is a highly localized electrochemical measurements and imaging technique using a simple, mobile theta pipet cell. Each channel is filled with electrolyte solution and a Ag/AgCl electrode, between which a bias is applied, resulting in a conductance current across a thin meniscus of solution at the end of the pipet, which is typically deployed in air or a controlled gaseous environment.SECCM

When the pipet is oscillated, an oscillating component in the conductance current is generated. This oscillating current component can be used to maintain gentle contact of the solution from the pipet cell with the surface and as a set point for high resolution topographical imaging with the pipet.

Simultaneously, the mean conductance current that flows between the pipet channels can be measured and is sensitive to the local nature of the interface, informing one, for example, on wettability and ion flow into or out of the surface investigated.

Conductor or semiconductor surfaces can be connected as a working electrode, with one of the electrodes in the pipet serving as a quasi-reference electrode.

This pipet cell then constitutes part of a dynamic electrochemical cell, with which direct voltammetric−amperometric imaging can be carried out simultaneously with conductance and topographical imaging. This provides multifunctional electrochemical maps of surfaces and interfaces at high spatial resolution.

Localized High Resolution Electrochemistry and Multifunctional Imaging: Scanning Electrochemical Cell Microscopy
N. Ebejer, M. Schnippering, A. W. Colburn, M. A. Edwards, and P. R. Unwin, Anal. Chem., 2010, 82 (22), 9141-9145


Scanning Electrochemical Microscopy (SECM)

Intermittent Contact - Scanning Electrochemical Microscopy

At warwick we have developed a new scanning electrochemical microscopy (SECM) tip positioning method that allows surface topography and activity to be resolved simultaneously and independently. The tip is oscillated normal to the substrate surface. Changes in the oscillation amplitude, caused by the intermittent contact (IC) of the tip with the substrate surface, are used as a feedback signal to control the tip height.

Intermittent Contact-Scanning Electrochemical Microscopy (IC-SECM): A New Approach for Tip Positioning and Simultaneous Imaging of Interfacial Topography and Activity

K. McKelvey, M. A. Edwards, and P. R. Unwin, Anal. Chem., 2010, 82 (15), 6334-6337.

Dual Carbon Electrodes

Dual carbon electrodes (DCEs) are quickly, easily, and cheaply fabricated by depositing pyrolytic carbon into a quartz theta nanopipet.

These Probes can be used in generation/collection (G/C) mode, the small separation between the electrodes leads to reasonable collection efficiencies of ca. 30%.

DCEs are employed in a scanning electrochemical microscopy (SECM) configuration. G/C approach curve measurements are shown to be particularly sensitive to the nature of the substrate, with insulating surfaces leading to enhanced collection efficiencies, whereas conducting surfaces lead to a decrease of collection efficiency. DCEs are used to locally generate an artificial electron acceptor and to follow the flux of this species and its reduced form during photosynthesis at isolated thylakoid membranes.

Individual nanometer-size electrodes can be functionalized through the selective deposition on to one of the two electrodes in a DCE while leaving the other one unmodified.

Fabrication, Characterization and Functionalization of Dual Carbon Electrodes as Probes for Scanning Electrochemical Microscopy (SECM)

K. McKelvey, B. P. Nadappuram, P. Actis, Y. Takahashi, Y. E. Korchev, T. Matsue, C. Robinson, and P. R. Unwin, Anal. Chem., 2013, 85(15), 7519–7526.

 Duel SECM example 

Combigned SICM-SECM

The easy and cheep fabrication and use of nanoscale dual function pH-scanning ion conductance microscopy (SICM) probes has been developed here at Warwick.

One Example of this type of probe incorporate an iridium oxide coated carbon electrode for pH measurement and an SICM barrel for distance control, enabling simultaneous pH and topography mapping. The fabricated probes, with pH and SICM sensing elements are typically on the 100 nm scale. The capability of the pH-SICM probe was demonstrated by detecting both pH and topographical changes during the dissolution of a calcite microcrystal in aqueous solution.

This system illustrates the quantitative nature of pH-SICM imaging, because the dissolution process changes the crystal height and interfacial pH (compared to bulk), and each is sensitive to the rate.

Fabrication and Characterization of Dual Function Nanoscale pH-Scanning Ion Conductance Microscopy (SICM) Probes for High Resolution pH Mapping

B. P. Nadappuram, K. McKelvey, R. Al-Botros, A. W. Colburn, and P. R. Unwin, Anal. Chem., 2013, 85(17), 8070–8074.

  SECM-SICM example