Micro Contact Printing - Technique Improvements

Technique Improvements

To help overcome the limitations set by the original technique several alternatives have been developed.

• High-Speed printing: Successful contact printing was done on a gold substrate with a contact time in the range of milliseconds. This printing time is three orders of magnitude shorter than the normal technique, yet successfully transformed the pattern. The process of contact was automated to achieve these speeds through a piezoelectric actuator. At these low contact times the surface spreading of thiol did not occur, greatly improving the pattern uniformity
• Submerged Printing: By submerging the stamp in a liquid medium stability was greatly increased. By printing hydrophobic long-chain thiols underwater the common problem of vapor transport of the ink is greatly reduced. PDMS aspect ratios of 15:1 were achieved using this method, which was not accomplished before
• Contact Inking: as opposed to wet inking this technique does not permeate the PDMS bulk. The ink molecules only contact the protruding areas of the stamp that are going to be used for the patterning. The absence of ink on the rest of the stamp reduces the amount of ink transferred through the vapor phase that can potentially affect the pattern. This is done by the direct contact of a feature stamp and a flat PDMS substrate that has ink on it.
• New Stamp Materials: To create uniform transfer of the ink the stamp needs to be both mechanically stable and also be able to create conformal contact well. These two characteristics are juxtaposed because high stability requires a high Young's modulus while efficient contact requires an increase in elasticity. A composite, thin PDMS stamp with a rigid back support has been used for patterning to help solve this problem.