Online Labs: Microcontact Printing

If you have any questions about this lab, please contact Joe Muskin at (217) 265-6481 or by email at jmuskin@uiuc.edu.

Purpose:

Computer chips and other electronic devices are manufactured by a process known as photolithography. However, this method is expensive and complex. Soft lithography by microcontact printing is a complimentary method that is cheap and simple. In this exercise you will use a method that plays an important role in the next generation of flexible and transparent electronics.

Materials:

PDMS Transparency master Petri dish Microscope slides Tollens' reagent 10% dextrose 1-hexadecanethiol solution (HDT) Silver etchant solution Tin (II) chloride Distilled water Paper towels Hair drier Q-tip swabs Plastic cups Lab detergent Disposable pipettes Scissors Disposable plastic knife

Click on the image above to open a full sized version.

Experimental Procedure

1. Flexible stamp fabrication.

   Generate and cut a pattern on a transparency leaving a border around the printing. Place printing side up in Petri dish.
   Add about 20 g PDMS elastomer and 2.0 g PDMS crosslinker to plastic cup.
   Stir for 5 minutes while mixture becomes more opaque. Pour into Petri dish and gently tap and blow to remove air. Place in 65° C oven to dry in 30 minutes or leave at room temperature until cured (at least 24 hours).
   Once the PDMS has cured (firm to the touch), carefully remove it from the dish. If it has not already come loose, pull the transparency master away from the underside of the PDMS. Cut around the pattern of the PDMS stamp with scissors or a utility knife.

2. Prepare Silver Substrate

   Prepare a clean, streak-free glass or plastic surface by washing in a detergent solution. Rinse thoroughly with distilled water.
   Soak the clean glass or plastic objects to be silvered in the tin(II) chloride solution for about 30 seconds. Remove the glass or plastic object, and rinse away all traces of the sensitizing solution with distilled water.
   While still wet, add enough Tollens' reagent to barely cover the surface of the glass or plastic. Do not overfill.
   Add a several drops 10% dextrose solution to the Tollens' reagent on the glass or plastic.
   After 60 to 90 seconds, rinse the silvered surface thoroughly with distilled water.
   Without touching the silver film, carefully shake off the excess water and dry it with a blow dryer.

3. Microcontact print

   Cover the stamp surface with HDT solution. Spread the HDT evenly over surface with cotton swab. Dry the stamp with a hair dryer.
   Place the stamp face down on a clean glass or plastic surface and apply pressure to the back of the stamp in order to remove excess HDT.
   Gently place stamp on the silver surface. Try not to trap air between the stamp and the silver coated surface.
   Carefully remove stamp from silver surface. Hold silver mirror in disposable cup of etchant solution until pattern is clear. Rinse silver thoroughly with distilled water. Dry the surface with a blow dryer. Do not wipe the silver film.

Downloadable Materials:

• Activity Guide

  Instructors guide containing all relevant information to conduct the lab.

  • MS PowerPoint (1.1MB)
  • PDF (400KB)
• Presentation

  Presentation for teacher to introduce the activity to students.

  • MS PowerPoint (7.0MB)
• Procedure

  Procedure with pictures of each step.

  • MS Word (52.0MB)
  • PDF (1.1MB)

Safety:

Goggles, gloves and aprons should be worn as in all chemistry laboratory activities. Avoid skin contact with PDMS or the crosslinker. In case of contact wipe off any material with paper towels, and wash the area thoroughly with soap and water.

Tollens' reagent should not be heated above 70° C and should not be evaporated to dryness. Silver nitrate solutions darken with exposure to light and, upon contact, will leave dark stains on skin or clothing. Concentrated ammonia is caustic, and it releases irritating ammonia vapor; thus, it should be used only under a fume hood or in a well-ventilated room.

Skin coming into contact with HDT or silver etchant should be washed thoroughly with soap and water. If either HDT or silver etchant comes into contact with the eyes, flush the eyes for 10 minutes at an eyewash station and seek medical help immediately.

Acknowledgements:

Thanks to Chaitanya Gupta for providing guidance and expertise.

Developers

David Bergandine, Joe Muskin, and Matt Ragusa