VS-SECM Scanning Electrochemical Microscope (CC and AC)

The SECM integrates a positioning system, a bipotentiostat and an ultramicroelectrode probe or tip. The positioning system moves the probe close to the sample surface, within the local image zone._cc781905 -5cde-3194-bb3b-136bad5cf58d_The bipotentiostat can polarize only the  probe  (feedback mode) or sample and probe independently (generator-collector mode), while measuring the resulting current(s). The probe is specially designed for have a specific conical polish ( according to the  RG ratio) and an active radius below 100 microns. The positioning system scans the position of the probe and charts it with measured electrochemical parameters, creating a local current data map.

Approximation curves (feedback mode) are used as an electrochemical means to position the Z-probe close enough 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 increased towards the sample. When the probe is close enough to the sample (a distance of 2 to 4 times probe diameter), the current measured at the tip changes from a global response to a local response. Over a region of high conductivity, a Nernstian response provides an enhanced local current over the global current . However, the local current decreases in relation to the global value in areas of low conductivity of the sample, since the transport of mass to the probe is difficult.

Common generator-collector mode experiments are similar to a rotating ring disk electrode (RRDE) experiment. In both cases, an electrode undergoes a redox reaction generating an electroactive product that is subsequently measured (“picks up”) 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. In addition, the system can be easily switched from sample generation: spike collection (SG-TC) to spike generation: sample collection (TG-SC), often simply by changing the polarization levels.

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

A new feature of the VS-SECM is the ability to perform AC-SECM measurements. The basic operation is the same as with the traditional DC-SECM, except that an AC signal is applied to the probe , rather than a CC-only signal. The resulting AC response is measured and the  magnitude  The phase of the impedance is represented based on the position of the probe. While DC-SECM always requires the presence of an electroactive species, _cc781905-5cde- 3194-bb3b-136bad5cf58d_often in the form of an additional mediator , AC-SECM can work with or without such a species. This technique has been used to map local electrochemical activity (eg, corrosion pitting), determine sample topography of insulators and probe for local surface conductivity (eg, 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, kinetics reaction, studies of porous membranes, evaluation of fuel cell catalysts and corrosion mechanisms.






 

• For the determination of localized electrochemical events such as electrode kinetics, metal dissolution and studies of biological samples

• Capable of approximation curve experiments and imaging modes in feedback mode and generator-collector mode

• The AC-SECM technique operates without the need for an electrochemical mediator, useful for corrosive systems

• Constant distance operation in conjunction with a survey survey technique (eg OSP) or constant distance SECM with EPFL Soft Stylus Probe technology