Noncontact Electrochemical Imaging with Combined Scanning Electrochemical Atomic Force Microscopy

Abstract

Combined scanning electrochemical atomic force microscopy (SECM-AFM) is a recently introduced scanned probe microscopy technique where the probe, which consists of a tip electrode and integrated cantilever, is capable of functioning as both a force sensor, for topographical imaging, and an ultramicroelectrode for electrochemical imaging. To extend the capabilities of the technique, two strategies for noncontact amperometric imaging-in conjunction with contact mode topographical imaging-have been developed for the investigation of solid-liquid interfaces. First, SECM-AFM can be used to image an area of the surface of interest, in contact mode, to deduce the topography. The feedback loop of the AFM is then disengaged and the stepper motor employed to retract the tip a specified distance from the sample, to record a current image over the same area, but with the tip held in a fixed x-y plane above the surface. Second, Lift Mode can be employed, where a line scan of topographical AFM data is first acquired in contact mode, and the line is then rescanned to record SECM current data, with the tip maintained at a constant distance from the target interface, effectively following the contours of the surface. Both approaches are exemplified with SECM feedback and substrate generation-tip collection measurements, with a 10-microm-diameter Pt disk UME serving as a model substrate. The approaches described allow electrochemical images, acquired with the tip above the surface, to be closely correlated with the underlying topography, recorded with the tip in intimate contact with the surface.

Electrochemical Biosensors - Sensor Principles and Architectures

“…In other words, the structural information is simultaneously correlated with chemical activity of the substrate [167]. These hybrid probes are, therefore, quite effective for the identification and chemical mapping of active surface sites [168]. Critical to the resulting synergy of AFM-SECM is the proper modification of the probe.…”

“…Critical to the resulting synergy of AFM-SECM is the proper modification of the probe. Please refer to the reference literature for information on the fabrication and application of various types of AFM-SECM probes [153,154,168]. Gardner et al have studied the correlation of membrane structure and transport activity across a synthetic polyethylene terephthalate (PET) membrane [169].…”

Peer Reviewed: Atomic Force Microscopy Probes Go Electrochemical

“…The low resonant frequencies of these SECM/ AFM probes require topographical imaging to always be carried out in contact mode ( Figure 1c), but electrochemical imaging can be carried out at either fixed height or constant distance (38) (Figures 1a and 1b, respectively). For fixed-height imaging, the feedback loop is disabled and the stepper motor of the AFM instrument retracts the tip a known distance from the surface of the sample.…”

“…Known as lift mode, this process has previously been used for magnetic and electrostatic AFM imaging. SECM/AFM probes are particularly effective for the identification and chemical mapping of active surface sites, as illustrated in Figure 5b (38). A 10-µm-diam platinum electrode sealed in glass and immersed in an electrolyte solution served as a model active site.…”

“…The substrate UME was biased at a potential sufficient to generate an electroactive species (IrCl 6 2-) from electrolysis of a solution mediator (IrCl 6 3-). The zone over which the tip collects IrCl 6 2-is clearly evident in the top part of Figure 5b (as a current flow at the SECM/AFM probe) and correlates well with the underlying location of the electrode, identified by topographical imaging in the bottom part of Figure 5b. The magnitude of the current measured at the tip electrode as a function of tip-substrate separation is quantitatively determined on the basis of models for diffusion from a diskshaped source (38).…”