Does anyone know how to measure sheet resistance of a material (polymer solution) using potentiostat?
You need 4 probes and 2 multimeters.
see http://en.wikipedia.org/wiki/Four-terminal_sensing
and http://en.wikipedia.org/wiki/Van_der_Pauw_method
that will explain you the theory of the Van Der Pauw method
The sheet resistance has a meaning for the polymer thin films, not the solution. After making the thin films by some deposition technique (dip-coating, spin-coating, printing, doctor blade, etc.) on some insulating substrate (glass, polymer foil, etc.) you can measure the total resistance. In the case of the square shape, you immediately have the sheet resistance (resistance for one square). Please keep in mind that the sheet resistance depends on various material parameters (i.e. polymer conductivity, solvent evaporation process (annealing time, atmosphere, etc.)) as well as film properties such as film thickness (higher thickness means lower sheet resistance). For better measurements, I recommend to have some conductive electrodes on the substrate to achieve good contact to your polymer films. For these electrodes you can use metals (e.g. fabricate by evaporation through the shadow mask) or you can use thin conductive oxides (ITO, ZnO, etc.) which will be patterned in an appropriate way.
You need 4 probes and 2 multimeters.
see http://en.wikipedia.org/wiki/Four-terminal_sensing
and http://en.wikipedia.org/wiki/Van_der_Pauw_method
that will explain you the theory of the Van Der Pauw method
You can modify an electrode with making a thin film of the polymer and use it as cathode in a cyclic voltammeter. After that you can easily measure the resistance of the material because you will have the forward current and voltage in this experiment.
@Martin, the square symbol in the units of sheet resistance has nothing to do with the square shape of a sample. It is there to indicate what youu are measuring. Probably you didn't mean it the wrong way but I foud what you wrote could be easily misunderstood.
Note added: please do not upvote this answer. As you can read below I was simply wrong here!
@Kai, sorry to disagree and for possibly being a little off topic but since resistance is proportional to length and 1/(crossectional area) = 1/(thickness * width), for a constant thickness of material it becomes proportional to the ratio of length:width, which for a square of any dimention is 1/1=1. Therefore a layer of substance with a 1 \Ohm sq. sheet resistance measures 1 \Ohm for a square sample of any size, at least in the theory of such things. In practice the current density is not likely to be perfectly even across the entire sample so measurements may vary. My point is however that the square in the Ohm sq. symbol refers precisely to a square shape of the theoretical sample on which the unit is based.
This is not to say that the sample itself needs to be square as long as the dimensions are known and an appropriate correction is made for the actual sample geometry being measured.
I made silicone rubber samples some time ago and used keithley electrometer to measure the surface resistance and the volume resistance..it was pretty simple as i used only two ring electrodes and the electrometer made the appropriate measurements and the calculations to give the obtained resistances..you can visit the website ot the keithley they have their document which explains how the electrometer works, probably it will give a pretty good idea of the how to.
As was already stated above, sheet resistance is a meaningful parameter only for relatively thin and uniform layers of solid materials.
For general understanding of the simple sheet resistance concept, I suggest to take a look at the "SEMICONDUCTOR MATERIAL AND DEVICE CHARACTERIZATION, 3rd ed.". Pages 11 and 12 are accessible at google.books:
http://books.google.cz/books?id=OX2cHKJWCKgC&lpg=PP1&pg=PA11#v=onepage&q&f=false
If resistance is high, than probaby you will have to use sandwich set up (electrode- polymer-electrode).
If resistance is low and substrate is rectangular, than you can use electrodes on top of the polimer. Prefered is to cover the whole oposite edges with the electrodes.(for example- 1/8 of the surface as electrode, 6/8 as m If you cover partially the oposite edges, then the extra material, that is not between the electrodes will also influence.
We measure the conductivity of thin film using Four Point Probe Methods or, for more accurate measurement you can use Wheatstone Bridge Method......
@Tariq Bashir
You mean I can convert the result from a multimeter to sheet resistance if the conductivity, right?
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