Why Are My 4-Point Probe Measurements Failing?

In summary, the person is seeking help with using the 4 point probe technique to measure the electrical conductivity of conductive polymer films. They have encountered several problems, including the films burning out, no voltage drop being detected in semiconducting samples, and the digital multimeter showing inconsistent voltage drop measurements. They are looking for advice and suggestions on how to properly conduct these measurements. One suggestion is to use a shunt resistor to limit the current through the sample and another is to use a lockin-amp or nanovolt meter for better results. Proper attachment of the leads to the sample is also mentioned as a potential issue.
  • #1
rury_cruz
4 point probe measurement help!

I will really appreciate if somebody can help me:

I was trying to measure the electrical conductivity of some conductive polymer films using the 4 point probe technique. Altough is widely described and seems easy to arrange, I have been unable to measure my samples due to the following problems:

1.- As soon as I turn on the power source the films burns out (like a fuse)due to the joule effect, I guess, even when I set the power source in the "constant current" mode, fixed to the minimum.
2.- When I tried to measure the electrical conductivity of the semiconducting samples, (or at least I thought so...), no voltage drop is detected between the inner probes, and no current flows at all. It seems to be "too insulating" to close the circuit
3.- The digital multimetter is always changing the voltage drop measurement, whether the current source is on or off. Could it be due to the connections?... some bi-metalic joint effect?

I hope some of you have done this kind of measurements before, I really need to know the conductivity of my samples. If you need further information feel free to contact me...
 
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  • #2
For the first problem you could put a shunt resistor in the cicuit to limit the current through the sample.

If the sample is insulating then you won't read a votlage across the inner leads.

A perferred method is to use a lockin-amp and measure the AC-resistance. It will give you a better S/N ratio. Otherwise you might need a nanovolt meter you get decent results.

How are you attaching your leads to the sample? This was a major problem that I ran into while making these type measurements.


JMD
 

FAQ: Why Are My 4-Point Probe Measurements Failing?

How does a 4 point probe measurement work?

A 4 point probe measurement is a technique used to measure the electrical resistance of a material, typically in the form of a thin film. It involves passing a known current through two outer probes, while the two inner probes measure the voltage drop. By using four probes instead of two, the effects of lead resistance are eliminated and a more accurate resistance measurement can be obtained.

What type of materials can be measured using a 4 point probe?

A 4 point probe measurement can be used on a wide range of materials, including conductors, semiconductors, and insulators. It is commonly used in the characterization of thin films, such as those used in electronic devices, solar cells, and coatings.

What are the advantages of using a 4 point probe over other measurement techniques?

One of the main advantages of a 4 point probe measurement is its accuracy. By eliminating lead resistance, the measurement is less affected by contact resistance and can provide more precise results. It is also a non-destructive technique, meaning the material being measured remains intact and can be used for further analysis.

How do I interpret the results of a 4 point probe measurement?

The results of a 4 point probe measurement will typically provide the resistance value of the material being measured. This value can be used to determine properties such as sheet resistance, resistivity, and conductivity. It is important to compare these results to known values of similar materials to ensure accuracy.

Are there any limitations to using a 4 point probe measurement?

While a 4 point probe measurement is a widely used and accurate technique, there are some limitations to consider. The technique is best suited for measuring thin films and may not be suitable for thicker materials. It also requires a uniform and flat surface for accurate results. Additionally, the material being measured must be electrically conductive.

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