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Making Thin Films by Spin Coating



A thin dye-doped polymer film is made by dissolving the dye and polymer in a solvent, flooding a substrate with the solution, spinning the substrate to throw off most of the material leaving behind a thin wet film, and driving away the solvent at elevated temperature. The step by step procedure is as follows.

Preparing the Solution

About 1cc to 2cc of solution makes one 2" by 3" film. To prepare a 12.5 gram solution (enough for making 6 to 10 films), add to a clean bottle with a magnetic stir bar the following ingredients in the order below:

  1. 7.12g of Propylene Glycol Methyl Ether Acetate (PGMEA)
  2. Dye (x grams), then stir until dye is dissolved
  3. 3.51g of gamma-Butyrolactone, then stir to make sure solution is uniform.
  4. Add polymer (y grams) and stir until fully dissolved.

For a 12.5 gram solution, a total of w=1.875g of solids is required. For example, to make 1% dye by weight in a polymer, use y = 1.8562g of polymer and x = 0.0188g of dye.

The proportions above are scalable if a different volume of solution is required.

Preparing the Substrates

Start with clean substrates (see cleaning substrates). If the substrates need mild cleaning, sonicate them in acetone and then rinse in distilled water. If they need more thorough cleaning, sonicate in 1M NaOH for 10 minutes, then dilute HCl for 10 minutes, and rinse with acetone then distilled water.

Spin Coating

To make films:

  1. Turn on the spin coater control unit and the vacuum pump.
  2. Set the spin speed and spin time.*
  3. Line the spin coater bowl with aluminum foil and lint free cloth to prevent the bowl from getting soiled.
  4. Draw the solution into a clean syringe.
  5. Place a Millipore filter on the syringe end (the filter is important for removing particulate contamination).
  6. Place the clean substrate on the vacuum chuck.
  7. Flood coat the substrate.
  8. Place the protective cover on the spin coater
  9. Step on the foot pedal.+
  10. After the motor has stopped, remove the protective cover, remove the film and place it on a foil tray in a clean environment (the film will be tacky, so dust will stick to it).
  11. Go to step 6 to make the next film.
  12. Once the desired number of films are made, place them in an oven set to 60 to 90 degrees Celsius (depending on the polymer) for several hours to insure that all of the solvent is removed. Baking overnight is recommended.
  13. Turn off vacuum pump and control unit.
  14. Clean the spin coater bowl.

Spin coating requires a clean environment to prevent contamination of the sample surface. It is advisable to do the whole process in a clean room or a clean area.

* Typical settings for making films on the order of 1 micron thickness is about 1,000 rpm for 30 seconds. Settings depend on the material, so some experimentation is required to get the desired thickness.

+ If the sample does not spin, TURN OFF THE SPIN COATER CONTROL UNIT and check the gasket on the vacuum chuck to make sure the seal is air tight.



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