If the molarity of my solution is varied then it is expected that the resistance will change. In my case the resistance decreases for SnO2 thin film as I change the molarity of the precursor solution from 0.1M to 0.2M. Can anyone help me with the explanation for the phenomenon or with any reference for the same. Thanks in advance.
A simple explanation is as follows. By increasing the molarity of the precursor you increase the thickness (D) of the resulting film. And resistance, in turn, is inversely proportional to D. It is interesting to point out that along with the decrease of resistance, an increase in molarity also results in a decrease of the optical band gap. Check Figures 3.9 and 3.10 from the attached chapter.
Hello Sandip
Sergei's explanation is logic, but still needs to be discussed. That is: assuming you use higher molarity for shorter time deposition to avoid high thickness what will then happen? Moreover, did you anneal the resulting films?? Annealing may enhance their characteristics, even if they have some more thickness..
I believe that you may still have a problem. With higher molarity you have higher deposition rate. You then have more nuclei formation. Higher deposition rate give films with smaller particles and with less uniformity and order.
So even if you get thinner films (by shortening the deposition time) you may still have difficulties.
The common wisdom is to deposit films at smaller rate by using different parameters (lower concentration of solution lower temperature, ....).
I believe you are depositing films by immersing the substrate in chemical precursors (as in chemical bath or SILAR technique). In these techniques, the higher molarity of the precursors usually increases the deposition rate and hence the thickness of the film (for a given period of deposition) as mentioned above. Although the higher rate of deposition is expected to negatively impact the grain size, in some of the cases it is not. It could be because the increase in thickness may have far more impact on grain size than the rate of deposition. In your case of SnO2 films, I would suggest you to do XRD studies of the films for 0.1M and 0.2M and then compare their grain size (by FWHM). If the grain size has improved in 0.2M then obviously its resistance will decrease due to the reduced grain-boundary
thank you fr the suggestion sir. Grain Size improvement mean the size reduces or increases in comparison with S1??
Grain size improvement means that the average grain size of the films increases. Usually, this is indicated by the sharpness of the XRD peaks. Some times the intensity of the peak will also increase. The quantitative measurements can be done by finding Full Width at Half Maximum (FWHM) of the peak and then plugging it into Scherrer formula. Alternatively, you can also confirm it by taking high resolution SEM images
SO Sir I am a bit confused. If the grain size is increased then how does the grain boundary decreases? If you can pls clear my doubt?
The entire film can be divided into grains and grain-boundary regions. The grain-boundary region is the region existing between two grains where there is no regular arrangement of atoms. Thus grain-boundary region is region of disorderliness.The grains, on the other hand, are the region where the atoms are arranged regularly in periodic manner (each grain is like a tiny crystal). Bigger the grain size, higher will be the space occupied by grains in the film and hence lesser will be the grain boundary regions. Thus as the grain size increases, the grain-boundary regions decrease.
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