I deposited the film using CBD ,but it's color does not change to yellow as expected.I changed the ratio of the chemicals but i got only white color not as supposed to be white to yellow color?
In CBD, it is important to adjust various parameters (like bath temperature, pH, solution concentration, molarities, etc) to obtain proper composition of thin films. I guess here that since the white color solution is not changing to deep yellow or yellow-orange color, the formation of CdZnS is not taking place properly. Please see that sufficient amount of temperature is provided to the solution bath. it is true that initially you have a white solution, which with material formation start to become deep yellow or yellow-orange in color. This strongly depends on Cd/Zn ratio, also.
The color of thin film is mainly due to the reflected light from the film. Pure CdS films are usually yellowish in color while pure ZnS films are usually light-white (depending on thickness). The alloy film Cd(1-x)Zn(x)S may vary in color depending upon the concentration of Cd and Zn in it. When x is close to 1, the film has more ZnS than CdS so the color may appear white. Similarly, when x is close to zero, the color could be yellowish.
Again, the color of the film depends upon the reflection spectra of the films which in turn depends upon the bandgap. If x=0.5, then technically the film must have equal amounts of Cd and Zn. At that pont, the bandgap of the material will be somewhere in-between that of CdS and ZnS. The color of the film will depend upon reflection spectra of the film at that bandgap.
I would suggest you to confirm the composition of the films by either EDAX or some other means. This would tell you whether the composition of the film is exactly same as what you expect from the composition of the precursors taken or not. You can also study the reflection spectra of the films and find the bandgap.
I agree with Gowrish Rao sir, its better to go for composition analysis of prepared sample and then decide for further analysis or re-synthesis.
Dear Raghad,
Preperation ZnCdS thin films using CBD is not easy because the formation of CdS is faster than ZnS thus, the control of preperation parameters is very important. You obtained white thin film and I ask you about the value of pH that you fixed? when using high value of pH the ZnO thin fim will form instead of ZnS or ZnCdS. You should test XRD to confirm the formation ZnO or not. Regards
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