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Soft Lithography

Patterning at the nanometer scale is an area of intense investigation, because current fabrication methods have their limitations at this length scale. For top-down approaches like lithography or imprint molding, the problem is making reproducible features smaller than 50 nanometers (nm). For bottom-up approaches like self-assembly, the challenge is patterning large areas with exact positioning. We have overcome these limitations by combining a molding step with a subsequent polymerization. The key to this novel strategy is including in the curable photopolymer used to make the initial pattern an "inimer," namely, a molecule with both an initiator and a monomer fragment for use in subsequent polymerization steps. Since some of the inimer's functionality remains exposed on the surface of the molded pattern, a second polymer can be directly synthesized onto the mold via living free-radical polymerization. Feature sizes between parts of the pattern can be reduced from a spacing of 100 nm down to 20 nm. Also, because several different polymers can be grafted onto the same initial molded pattern, it is possible to use these same basic processing steps to change the surface chemistry.

Secondary Living Polymerization

Secondary Living Polymerization Scheme

 Contact Molding Process

Contact Molding Process

Before Polymerization

SEM of lines before graft polymerization

 After Polymerization

SEM of lines after graft polymerization

see
Timothy A. von Werne, David S. Germack, Erik C. Hagberg, Valerie V. Sheares, Craig J. Hawker, and Kenneth R. Carter, "A Versatile Method for Tuning the Chemistry and Size of Nanoscopic Features by Living Free Radical Polymerization", J. Am. Chem. Soc., 125, 3831-3838, 2003.
M. Husemann, D. Mecerreyes, C.J. Hawker, J.L. Hedrick, R. Shah, N.L. Abbott, "Surface-Initiated Polymerization for Amplification of Self-Assembled Monolayers Patterned by Microcontact Printing", Angew Chem. Int. Ed. Engl., 38, 647, 1999.
M. Husseman, E. E. Malmström, M. McNamara, M. Mate, D. Mecerreyes, D.G. Benoit, J.L. Hedrick, P. Mansky, E. Huang, T.P. Russell, C.J. Hawker, "Controlled Synthesis of Polymer Brushes by "Living" Free Radical Polymerization Techniques", Macromolecules, 32, 1424, 1999.