Using the Jandel 4 point probe assumes you are measuring a thin film with respect to the spacing of the probe points.  Spacing is typically 1mm so any film less than 0.1mm should be fine.  Also the wafer should be infinitely large.  As long as the wafer is greater than 25 x 25mm large the error will be small. Typically less than 1%.

To convert ohms/sq into S/m you need to measure the thickness of the film using a profilometer or an AFM.

conductivity (S/m) = 1 / (R x t)

where R is in ohms/sq

t is film thickness in m.

Example:  You measure 25 ohms/sq and film is 120 nm

conductivity = 1 / (25 x 120 x 10^-9) = 333333 S/m or 3333 S/cm

Hope that helps.

cheers

Rick 

4 point probe gives you sheet resistance (lateral).  Many times in thin films, the conductivity (electrical and thermal) are anisotropic, so vertical conduction could be different.  Which direction are you interested in, and is this a metal or semiconductor?  How thin?

conductivity = 1/ reisistivity

Engineeringtoolbox.com has unit converters

thank you dear john

i am M.S student of chemistry  

i am working on water soluble (dispesible) graphene

synthesis, characterization, structure & properties calculation, also further application of water soluble graphene is main part of my thesis and all of them proceeded.

at final step of my work i want to prepare a thin film of water soluble graphene on surface by wet chemical method (making a thin dispersion of water soluble graphene on surface then consolidate it).

now i want to calculate it's conductivity by using 4 point and report this value in (S/cm) unit.

i find some method to change (Ohm/sq) to (Ohm/cm) and (S/cm)

You can pass from sheet resistance to resistivity by considering that the sheet resistance is the surface resistance of a material in form of thin film.

By taking in consideration two superficial contacts 1 cm large, placed at a distance of 1 cm one from each other and measuring the resistance between these contacts the sheet resistance of the material is obtained, once normalized for the thickness of the film. Consequently, given the sheet resistance dividing by the film thickness, the resistivity in Ω cm is obtained.

Graphene is definitely anisotropic, so conduction through the film vertically will be different than along the film laterally.  Sounds like an interesting experiment.  

thanks for your answers

I assume you mean you're using a Jandel 4 point probe?  Good piece of equipment.  Make sure you are using an appropriate drive current to do the measurements.  You want the measured voltage drop to be about 50-100mV.  Make sure to take the average of both the forward drive current and the reverse drive current so as to take into account any contact voltage drops with the 4 pins on the sample.

To convert ohms/square you MUST measure the thickness of the film in cm using a profilometer.  Something like Dektak profilometer would be perfect.  You CAN NOT obtain S/cm without knowing the film thickness.

conductivity (S/cm) = 1/(R x t)

where R is ohms/square and t is film thickness in cm

Hope that helps.

tank you manrico

your answer is helpful for me,

i used SEM cross-section for thickness calculation. its about (7-10) micrometer.

...

If you're wanting to report in S/cm make sure you convert 7 micron into cm.  7x10-4 cm.  good luck with your project.

thanks a lot

Nobody uses the Van der Pauw method for this?

Hi I used both the Van der Pauw and four point method to measure the sheet resistance of silicon wafers, and found that the results from the four point measurement are more accurate and consistent. 

It could also be that I am using the Van der Pauw method wrongly - as I understood, the points where I apply current and measure the voltage are arbitrary? 

Using the Jandel 4 point probe assumes you are measuring a thin film with respect to the spacing of the probe points.  Spacing is typically 1mm so any film less than 0.1mm should be fine.  Also the wafer should be infinitely large.  As long as the wafer is greater than 25 x 25mm large the error will be small. Typically less than 1%.

To convert ohms/sq into S/m you need to measure the thickness of the film using a profilometer or an AFM.

conductivity (S/m) = 1 / (R x t)

where R is in ohms/sq

t is film thickness in m.

Example:  You measure 25 ohms/sq and film is 120 nm

conductivity = 1 / (25 x 120 x 10^-9) = 333333 S/m or 3333 S/cm

Hope that helps.

cheers

Rick 

Is there a way to measure conductivity of thin liquid films?

resistivity is equal to sheet resistance multiply by thickness

I second Zainab. If you have the sheet resistance of the film measured by the 4-point probe provided you satisfy all the assumptions of the simplified expression:

Rs= sheet resistance = 4.44 V/I where V is the four point probe voltage and I is it current. The sheer resistance = the resistivity roh/ t the thickness of the film.

To get roh= Rs.t , which is the expression brought by Zainab.

The most important requirement for the validity of the above expression:

-The substrate must insulating

- The extention of the film must be much greater than s the probe spacing

- The probe spacing must be much greater than the film thickness

- The material is homogeneous

Best wishes