VS-SECM (DC and AC) Scanning Electrochemical Microscope

The SECM integrates a positioning system, a bipotentiostat, and an ultramicroelectrode probe or tip.  The positioning system moves the probe close to the surface of the sample, within the local imaging zone. The bipotentiostat can polarize the probe only (feedback mode) or the sample and the probe independently (generator-collector mode), while measuring the resulting current(s). The probe is specially designed to have a specific tapered polish (per the RG ratio) and active radius below 100 microns. The positioning system scans the probe and charts position with measured electrochemical parameters, creating a data map of local current.

Approach Curves (feedback mode) are used as an electrochemical means by which to position the probe in Z sufficiently close to the sample to be in the local imaging zone. A DC voltage is applied to the probe, while the DC current response is plotted as the probe is incremented towards the sample. When the probe is sufficiently close to the sample (a distance of 2-4 times that of the probe diameter) the measured current at the tip transitions from a bulk response to a local response. Over a region of high conductivity, a Nernstian response provides a local current enhanced over that of the bulk current. However, local current is decreased relative to the bulk value over areas of low conductivity of the sample as mass-transport is hindered to the probe.

The common Generator-Collector Mode experiments are similar to a Rotating – Ring Disk Electrode (RRDE) experiment.  In both cases, one electrode undergoes a redox reaction generating an electroactive product that is subsequently measured (“collected”) at the other electrode where it undergoes another redox reaction.  A SECM monitors these reactions while adding the extra dimension of spatial resolution to the data.  Additionally, the system can easily change from Sample Generation – Tip Collection (SG-TC) to Tip Generation –Sample Collection (TG-SC) often by simply changing polarization levels.

Standard SECM probes are rigid and made of a noble metal, such as Pt, imbedded in glass.  The Soft Stylus Probe technology from LEPA-EPFL, Switzerland, offers a convenient method of controlling the probe to sample distance without the need for complicated feedback electronics.  These constant distance measurements are especially important when sample topography can affect the electrochemical response, such as in the case of corrugated surfaces.  In addition, the soft probe technique has been shown to be ideal for soft tissue samples and has been applied to the detection and staging of cancer.

A new feature of the VS-SECM is the capability to perform AC-SECM measurements.  The basic operation is the same as with traditional DC-SECM except that an AC signal, rather than a DC only signal, is applied to the probe.  The resulting AC response is measured and the impedance magnitude or phase is plotted as a function of probe position.  While DC-SECM always requires the presence of an electroactive species, often in the form of an added mediator, AC-SECM can be operated with or without such a species.  This technique has been used to map local electrochemical activity (e.g. formation of corrosion pits), determine sample topography of insulators, and probe local surface conductivity (e.g. surface defects).

Since the imaging mechanism of all forms of SECM is electrochemistry, the applications of a SECM are as varied as the applications of electrochemistry itself.  Some key applications include biological sensors, reaction kinetics, porous membrane studies, fuel cell catalyst evaluation, and corrosion mechanisms.

  • Documents +

  • Specifications +

    Compliance Voltage ±12V  
    Polarizations Voltage ±10V  
    Potentiostat  Current Range Resolution 
    VersaSTAT 3
    VersaSTAT 3F
    VersaSTAT 4
    VersaSTAT 3/3F/4 w/VersaSTAT-LC Option
    PARSTAT4000/+/A w/VersaSTAT-LC Option
    200nA to 650 mA
    4nA to 650mA 
    4nA to 1A
    4pA to 200mA
    40pA to 20A
    80fA to 200mA
    -Compatible with internal and/or external boosters to expand maximum current capability.
    -EIS enabled.
    *Please see potentiostats brochure for detailed specifications on the models

    10 micron Pt probe with RG ratio of ~ 10
    25 micron Pt probe with RG ratio of ~ 10
  • Options +

    L-Cell VersaSCAN L-Cell
    • Screws into optical table of VersaSCAN
    • Approximately 1 Liter in volume
    • Level adjustment mechanism
    • Accepts large flat samples and 32-mm diameter mounted samples
    • Recommended for all techniques, particularly LEIS, SVET, SKP, SDC, OSP
    mL-Cell VersaSCAN mL-Cell
    • Screws into optical base of VersaSCAN
    • Approximately 7 mL in volume
    • Level adjustment mechanism
    • Accepts a range of samples including 32-mm diameter mounted samples and non-standard samples
    • Specifically engineered for low-volume SECM applications
    VersaCAM VersaCAM
    Long Working Distance Video Microscope
    • Camera:
      • Color
      • Number of pixels: 795 (H) x 596 (V)
      • Minimum illumination 0.02 lx. F1.2
      • Power: 12V DC ±10%
      • CS-mounted or C-mount with provided adapter
    • Lens:
      • C-Mount
      • Manual focus
    • Display:
      • 8 inch color TFT display
      • PAL & NTSC auto selection
      • 640x480 (307,200 pixels) screen resolution
  • Video +

    Watch video demonstrations of the VS-SECM (DC and AC) Scanning Electrochemical Microscope

  • Experiments +

    Approach Curve Approach Curves measure current as the probe position is incremented in the Z-direction approaching the sample. Typically, these experiments are first ran over known areas of insulating nature to show negative feedback….then over areas of known conducting nature to show positive feedback. By comparing the results of these two experiments, you can successfully position the probe at the appropriate Z-distance for a SECM experiment.
    Line Scan SECM Line Scan experiments allow you to polarize either the probe or sample at a potential sufficient to cause an electrochemical reaction. Current is recorded as the probe’s position is scanned in either the X or Y direction. If the “Secondary Potentiostat” is connected Generator-Collector experiments are possible, as the probe and sample can be independently polarized.
    Area Scan SECM Area Scans are X-Line Scan experiments at incremented positions in the Y-direction. This XY plane is graphed as a map.
    Non-Scanning, Fundamental Experiments The VersaSTAT's can run a wide variety of non-scanning fundamental experiments with the VersaStudio environment. Please reference the brouchure or webpage of your specific model of potentiostat for complete details on its non-scanning experiments.