I am trying to coat "Bismuth Ferrite" solution (0.5 Molar) on "Nb doped Strontium Titanate". The solution is prepared by Sol-Gel method, and "Ethylene glycol" and "Acetic acid" are used as solvents. After cleaning the surface of "SrTiO3" by Distilled water and acetone and drying it by "Nitrogen Gas". I used spin coating to coat only single drop of the solution on the surface of the substrate, but during and after the calcination there are always tiny air bubbles on the surface of the sample (only visible in higher magnification).
Optimize the solution concentration. Before dropping the spin coating solution, make sure that it is bubble free. Pay attention while dropping the solution on the support without forming any tiny bubbles inside. Optimize the RPM.
Good Luck
Lijo
Thanks, but don't you think that it is forming during calcination step and because of solvent evaporation ? I think when we have more viscous solution on the surface it makes "solvent evaporation" more difficult and traps the the air bubble. Don't you think so ?
Yes, if solvent cannot escape completely before calcination, there is a possibility to form tiny bubbles due to evaporation. Do calcination by increasing the temperature in slight increments.
Try ultrasonic device to remove the bubbles or use type of solutions that has surface tension very high like water some drops ( water can not form bubbles but soap can form bubbles)....best regards
During deposition process try to deposit layer by layer (in case of multiple layer) by drying the each step. And the process should be optimized before the final coating specially rpm , because rpm needed to be optimized depends upon solvent type (volatile or non -volatile), viscosity and ease of dropping and site of dropping.
You can try to change your solvent with higher a boiling point one...for example if you will use chloroform with spin coating, your film will be usually terrible...
Also if you are coating your material on an ITO or FTO cleaning process of the substrate is so important...and try not to put so much solution on your substrate....
I added more details on top, It may helps you. Actually I am looking for method to avoid the bubbles without changing the solvents.
You should try to modificate solvent properties, surface tension, hydrophilic or hydrophobic properties of the SrTiO3, or try to optimize the annealing process of your 2nd coated thin film...
Thats all I can offer...
You could try to degass the solution for 20 minutes (or until you see no small bubbles in it) and then pour it on top of the surface cautiously to avoid air bubbles trapping between the surfaces...
What if the coated substrate is placed in a vacuum chamber? The bubbles will surely pop out.
But I am not sure how this procedure will affect the quality of the film since the solvents will surely evaporate faster.
Actually the whole procedure of spin coating is happening in vacuum chamber. The substrate is fixed on the stage. after droping the solution on it we close the chamber and vacuum it, and eventually it start spining (7000 rpm).
Could you find that how to avoid air bubbles on the surface of the film? I have the same problem like you. I'm using PGMEA as solvent.
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