Hello
I would like to measure electrical conductivity (resistivity) of electrospun fibermat of a polymer.
I know that:
Knowing the thickness of the fibermat, one should be able to apply it in the conventional test. Through this measurement, one can calculate conductivity through a correction factor by measuring the voltage and knowing the current applied.
The problem is:
Even when the lowest current value (2 nA) is applied, the instrument does not show enough stability of the current flow, and no voltage reading will be obtained.
What should I do?
I think the 4-point probe method is supposed to apply to semiconductor and non-conductor materials as well.
Does changing compliance help?
I am using one Keithley instrument as my current source and another one to read the voltage.
I would be grateful to have helpful comments.
Hey Ali,
a bachelor student I am supervising is building a similar setup at the moment. We chose the Van der Pauw method (see https://en.wikipedia.org/wiki/Van_der_Pauw_method). I don't know if you are trying a regular four point probe method (with contacts in line) or VdP with a square shape of the contacts but I hope that a brief recapitulation of what we did may help you:
We also use one Keithley 2400 as current source and one Keithley 2000 for measuring the voltage. We tested our setup on SiOx samples (5x5mm²) with 50nm to 100nm of copper deposited by EBPVD and we got good results with a current of about 100mA. For higher currents we heated the sample and the contacts. Maybe you should try higher current.
For our tests the sample holder was rather simple. Just 4 bolts with springs and and sharpened and bend copper sheets as contacts. We also noticed some instability in the measurements, mostly due to heating the contacts or touching the sample holder or the desk. Low resistance contacts are important for this kind of measurements.
For the next iteration we want to use test pins from microelectronics as contact needles
You mention compliance - is this light flashing on the keithley current source? If so it means it can't supply the current you select with the given voltage compliance. On a Keithley Current Source, the compliance setting is a safety to limit the maximum voltage it will go to, to drive the current. For sure if it is flashing (depends on keithley model how it tells you), you are out of compliance and thus you don't have the 2nA you set as it can't supply the voltage required to get there. This will give unstable current readings. You can increase this compliance voltage to the maximum your device / safety can allow and then try. What model Keithleys are you using?
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