Questions & Troubleshooting
I had a problem with the way the last aluminum samples turned out. It looked like there were almost pin holes or something in the aluminum layer. I am not sure if you know what may have been wrong but I can show you the samples and maybe you have an idea of what caused it.
The pinholes are most likely caused by contaminates on the substrate , below are some more comments K.S.
Dr A. Kumar
Harcourt Butler Technological Institute
Dear Dr. Sivagami
Deposit the film at higher vacuum than what you are using at present. For good adhesion, Degass the substrates before deposition. Make slightly thicker films. Anneal them after evaporation in vacuum at higher temperatures for getting rid of voids. See if you are able to solve the problem. Substrate cleaning can also be improved for better uniformity. Good luck.
Dr A. Kumar
Harcourt Butler Technological Institute
If substrates are glass plates, degassing is done by putting a heater inside the coating unit over the substrates and heat them up to 200 degree centigrade for about two hours in vacuum. The gasses absorbed comes out in this process. Switch off the heater to cool down to room temperature. Thereafter, deposit the film without exposing them to air.
Pradip Kumar Dey
Added an answer
pinholes are mainly created due to any foreign material already present in the substrate and they tries to come out through the deposited films during deposition. Clean your substrate thoroughly in piranha solution (1:1 ratio of H2O2 and H2SO4 for 20 min. ** you can search in net for details) . Thereafter rinse in DI water and preheat in oven @ 150 deg. Cent. for at least 30 min and then place in thermal chamber for deposition. Also you should heat your substrate up to 150 deg. cent. just before deposition. For better film quality high vacuum is essenti
Reed Schmell
Independent Researcher
Pinholes are either caused by surface contamination remaining on the "cleaned" surface. Use the water break test to determine if the surface is residue free. You will see interference fringes as it dries. The fringes will be even as the water evaporates. Any island fringes or streaks means the surface is not clean. Any of these particles actually become nucleation sites as the coating is deposited