4-Probe measurements in modified Indium tin oxide(ITO) coated glass substrates.
I am carrying out resistivity measurements using the 4-probe ITO on my sample which are small rectangles (1x2cm).
My doubt is in relation to the performance of the experiment, would it be correct to position the 4-probe exactly, in the center of the rectangle or collect measurements at different points in the sample?
Because I noticed that when varying the measurement location, the resistivity of the material varies.
Mateus Siraque I assume you have an edge effect as the field arcs outward. Have you not got larger pieces? If not, measure in the center. What color does the ITO film appear to be? Without color/transparent? Do you have a specification for the material or did you make yourself?
@Mateus Siraque
A four point probe technique is to measure the sheet resistance of a conducting surface. The formula of a surface resistance is obtained by assuming the probe dimension is much smaller than the measured surface area. If you have a limited conducting substrate, the four probes must be relatively small size in order to measure the surface resistance accurately.
There is the detail below for how to derive the resitivity formula which gives you an idea how to use the four point probe correctly.
http://four-point-probes.com/four-point-probe-manual/
Hope it helps
If the distance between probes is the order of 1 mm or smaller and your
sample is 10mm x20 mm then measurements performed at the center of the sample then the sheet resistance corrections associated with the finite size
of the sample are small.
Differences between results of the sheet resistance measurements at different probe position have the following origins: 1) vicinity of sample edges
2) Nonuniform thickness of ITO film, 3) Nonuniform conductivity of ITO film
Note that corrections for the probe position on the finite sample having
uniform sheet resistance are possible but requires numerical solutions of Laplace equation.
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