Recently, I'm trying to synthesize CdS sol-gel, thereafter preparing CdS film by spin-coating. But I found the formed CdS sol didn't appear the color of clear yellow, but in milk white. And after placing for a day, the "solution" became layered, I doubt that the CdS didn't form actually, which could confirm my guess is that when I heating the "solution", it became yellow.
Anyone give me any suggestion or discussion would be welcome and receive my thanks!
The references I refered to showed as follows:
http://xueshu.baidu.com/s?wd=paperuri%3A%28ad5ab9881d561daeb83aa919e76ab9c9%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fiopscience.iop.org%2F1757-899X%2F149%2F1%2F012051%2F&ie=utf-8&sc_us=9710111922815292613
http://xueshu.baidu.com/s?wd=paperuri%3A%288210a402da6f232f6b97b5fce8efc4b7%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0925838816340075&ie=utf-8&sc_us=7616361404557696825
Do you need to get a film or nanoparticles? To obtain yellow nanoparticles, solutions of a soluble cadmium salt Cd(NO3)2 and a soluble sulfur salt Na2S in a stabilizer solution PEG are mixed. In your link receive a film with thiourea. Thiourea not reacts with a cadmium ion with the formation of cadmium sulphide. First, a complex with a coordination bond is formed, and then, when the film is heated, a cadmium salt is formed. Therefore, the color in the beginning can be different. Instead of thiourea, I would experiment with Na2S.
Best regards.
Dear Yuri,
Thank you so much. I need to get a CdS film. You remind me of the importance of reagent, and I'll try to see if Na2S work.
With my regards.
In addition to Yuri Mirgorod,
If you are using thiourea for S, use hydrothermal for synthesizing the CdS NPs.
Thank you, Darshan,
I've tried by using Na2S and found that the "solution" was turbid yellow liquid after the reaction finished, in addition, the as-synthesized solution turned into a jellylike colloid after the placement of a day, beyond that, I stired it violently to see what may happen, the result is that the colloid broke into numerous granules and gathered into clusters(as the following picture showed).
I guess now the "solution" probably compose of NPs or larger particles, but I want to use it to prepare CdS thin film by subsequent spin-coating, not NPs. So, should I carry out the spin-coating immediately after the reaction ended, rather than waiting for a day?
Another problem is that some literatures reported that the CdS sol-gel is clear yellow color, but my product not clear enough with particles suspending in the solution all the time, it's really perplexing...
Spin-on deposited sol-gel films are usually amorphous. A thermal treatment is one of the ways to crystallize CdS. By optimizing the anneal conditions you'll get your targeted average crystal size. You will see the change of color and the optical absorption spectra as far as it happened.
Keep in mind: nano-crystalline films are not very stable in ambient and require a passivation of some kind. If you are targeting the optical application, they might be crystallized in-situ in the transparent optical media. That media (SiO2, TiO2, etc. might serve as a passivation .
Dear Marina,
I understand that materials in size of nanometers (e.g. nano-crystalline films) have different properties compared with macroscopical subject, due to relevent quantum effects. I think that's one important reason why films are not very stable in ambient environment, in addition, another cause is the atoms exposed in the surface of films possess more energy than the inner one, which are more active to induce reaction.
Well, the annealing of CdS films you mentioned is a useful suggestion. Anyway, thank you so much.
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