Hi,
I am currently struggling to achieve a uniform thin film coating of Zinc oxide nano particles for use in QD-LED device.
I have many papers detailing similar steps towards achieving the above but I have not been able to.
I made 40mg/ml solution of ZnO NPs dispersed in a 1:2 (IPA:MeOH) solvent and toluene. Attached is an image of the IPA:MeOH mix (1500rpm for 30seconds).
The toluene samples appeared to create a better film with less aggregation but still not satisfactory.
I have varied the speed settings from 1000rpm to 5000rpm, time from 30 seconds to 2mins and the quantity of ink used from 100ul to 500ul without thin film being achieved.
Annealing makes not noticeable difference to the final product.
I am about to test dispersing the ZnO NPs in PMMA to see how this fares.
Would any be able to provide any feedback on the steps I have taken so far if there is anything noticeable that I am missing to achieve thin film?
I have read though the FAQ section of the ossila website for how to counter the streaking defects I am experiencing but with no luck.
Must I employ a purification step or specific dispersion technique when making my solutions for deposition?
Thank you.
Dear Joshua,
How big average sizes of your ZnO nanoparticles are? This could affect your coating significantly. We normally use very diluted solution i.e. 1 to 5mg/ml and employ a spray-coating technique. It works very well. Alternatively if we use ZnO films, we intend to use ZnO precursor.
Best wishes
Xuhua
Hi Joshua Mcdonald
If you are making ZnO thin film from the zinc oxide ,dispersion. You can dilute it with ethanol(depending upon your concentration), for mine that I use in random lasing I make it 10% conc (by volume). Then you can spin coat it on the substrate (usually glass cover slips) at 500 rpm for 15 s and then at 5000 rpm for 45 s. Finally place it on hot plate maintained at 300 0C for 2 min to evaporate the ethanol. It works well with me to get uniform film of ZnO
Bibek S Dhami thanks for your response. Out of curiosity do you find a large difference in the layer formed between the first and the second coatings?
Xuhua Wang thank you for your response. Do you happen to know how thick your ZnO layer is with those factors that you mentioned?
Joshua Mcdonald I don't get what you mean by first and second coating. If you are talking about the two spin coating rates I mentioned earlier, first rate (500 rpm) was just to evenly distribute the ZnO solution where as the second rate (5000 rpm) determines the thickness of your film.
Joshua Mcdonald The good thing for the spray coating is that you can control the thickness easily by the spraying coverage using the numbers of coating cycles. Normally we use 15 to 30 nm thickness range in the device fabrication.
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