svet overview

8/12/2019 SVET Overview

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SVET OverviewAdd to Quote Request

The Scanning Vibrating Electrode Technique uses a single wire to

measures voltage drop in solution. This voltage drop is a result of

local current at the surface of a sample. Measuring this voltage in

solution images the current at the sample surface. Current can be

naturally occurring from a corrosion or biological process, or the

current can be externally controlled using a galvanostat.

A piezo unit vibrates the probe in Z-direction (axis parallel to the

sample). The amplitude of vibration may be only 10s of microns

peak-to-peak. This small vibration provides a very small voltage to be measured.

Therefore, the response (signal + noise) at the probe is then gained by the electrometer. The gained output

of the electrometer is then input to a Lock-In Amplifier. This, in turn, uses a phase detector along with aReference at the same frequency of vibration to extract the small AC signal from the entire measured

response. The VersaSCAN capitalizes on Ameteks industry-leading Noise Characteristics of the Signal

Recovery 7230 Lock-In Amplifier to provide superior measurement of these small signals.

The voltage recorded and the probe is repositioned. A data map results as voltage versus position are

displayed.

A key application of SVET is to study corrosion process of bare metals. These metals could be galvanic

couples or these could occur from local non-uniform corrosion events, such as pits or crevices.

Time-lapse experiment series provide the capability to literally watch the corrosion events happen as

different areas passivate and activate.

Additionally, there are many applications and references for the use and results of SVET used in biological

systems.
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Kelvin probe force microscopeFrom Wikipedia, the free encyclopedia

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In Kelvin probe force microscopy, a conducting cantilever is scanned over a surface at a constant height

in order to map the work function of the surface.

Kelvin probe force microscopy(KPFM), also known as surface potential microscopy, is a noncontact

variant ofatomic force microscopy(AFM), and was invented in 1991.[1]With KPFM, thework functionof

surfaces can be observed atatomicormolecularscales. The work function relates to many surface

phenomena, includingcatalytic activity,reconstruction of surfaces, doping and band-bending of

semiconductors,charge trapping indielectricsandcorrosion.The map of the work function produced by

KPFM gives information about the composition and electronic state of the local structures on the surface of a

solid.

KPFM is a scanning probe method where thepotentialoffset between a probe tip and a surface can be

measured using the same principle as a macroscopic Kelvin probe. The cantilever in theAFMis areference

electrodethat forms a capacitor with the surface, over which it is scanned laterally at a constant separation.

The cantilever is not piezoelectrically driven at its mechanicalresonancefrequency 0as in normalAFM

although an alternating current (AC) voltage is applied at this frequency.

When there is a direct-current (DC) potential difference between the tip and the surface, the AC+DC voltage

offset will cause the cantilever to vibrate. The origin of the force can be understood by considering that the

energy of the capacitor formed by the cantilever and the surface is

plus terms at DC. Only the cross-term proportional to the VDCVACproduct is at the resonance frequency 0.

The resulting vibration of the cantilever is detected using usual scanned-probe microscopy methods

(typically involving a diode laser and a four-quadrant detector). A null circuit is used to drive the DC
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potential of the tip to a value which minimizes the vibration. A map of this nulling DC potential versus the

lateral position coordinate therefore produces an image of the work function of the surface.

A related technique,electrostatic force microscopy(EFM), directly measures the force produced on a

charged tip by the electric field emanating from the surface. EFM operates much likemagnetic force

microscopyin that the frequency shift or amplitude change of the cantilever oscillation is used to detect the

electric field. However, EFM is much more sensitive to topographic artifacts than KPFM. Both EFM and KPFMrequire the use of conductive cantilevers, typically metal-coatedsiliconorsilicon nitride.
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