my sample is cadmium oxide deposited on Fluorine doped Tin Oxide (FTO) Glass . where cadmium oxide and FTO are electrically conductive .
how can i measure the resistivity of CdO without addition from FTO ?
My advice would be measure the resistivity of your sample and the resistivity of your bare FTO substrate without CdO respectively. And the resistivity of your sample can be regarded as the resistivity of FTO and that of CdO in parallel. That is based on the assumption that a) your current probes are far enough from your voltage probes so that the current has already distributed between two layers according to their different resistivity; b) your FTO and CdO films are uniform enough so that the distribution of current is also uniform between the two voltage probes.
The four-probe method used for resistivity measurements of thin layers on substrates with different value of the specific resistance or the conductivity type. In the simplest case, the layer should be located on insulating or high-resistance substrate. If the layer has the opposite to the substrate conductivity type, the p-n junction forming at the interface isolates the layer and the substrate from each other. However, the resistance measurement in epitaxial films on low-resistivity substrates even of a different type conductivity must performed at not too high currents. And even in this case, there are a number of difficulties.
My advice would be measure the resistivity of your sample and the resistivity of your bare FTO substrate without CdO respectively. And the resistivity of your sample can be regarded as the resistivity of FTO and that of CdO in parallel. That is based on the assumption that a) your current probes are far enough from your voltage probes so that the current has already distributed between two layers according to their different resistivity; b) your FTO and CdO films are uniform enough so that the distribution of current is also uniform between the two voltage probes.
i forgot some information in question (i prepared my sample by electrodeposition method )so ,i can not do your opinion dr.Tianyi , because i can not measure CdO without FTO ,and i can not make them parallel when measure resistance ,because CdO is deposited on one surface of FTO and the other surface of FTO isolated
Well, I understand that you cannot measure CdO without FTO. That is why I measure the resistivity of your sample (By "sample" I mean FTO coated with CdO) and also measure the resistivity of bare FTO susbstrate. And the resistivity of CdO can be calculated by
1/R_CdO=1/R_sample-1/R_FTO
Is that clear?
then , can i measure conductivity of CdO after measured the resistance of it by four point probe ?
Dr. Li Tianyi clearly indicated the answer: Yes, it is possible to measure the resistivity of CdO without addition from FTO. But considering the number of reservations and comments. In particular, we must remember that the current that is generated in the FTO substrate (flowing through the substrate) still passes twice through the thickness of the CdO film (current probes), and the voltage probes are not in contact with the substrate directly, but through film too. It gives an error in the measurement result.
Sequence of actions: 1) measure the substrate. 2) apply the tape. 3) perform measurements on the prepared heterostructure CdO/FTO. 4) spend calculation.
Or you can spend individual measurements on the heterostructure, and on the other identical substrate.
Best regards,
AM
Hi Hasanin,
Please measure under low current supply because when we increase the current supply, more electric field lines goes deeper into the sample. In such case, if you increase the bias current, E fields may cross the CdO and see the FTO, and you will get the combined results, which will be difficult to analysed.
Make sure that your four probes do not purges your sample and make direct contact with the FTO substrate.
Good luck.
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