Biography:
Jim Watkins is a Professor of Polymer Science and Engineering and Director of the Center for Hierarchical Manufacturing, a National Science Foundation Nanoscale Science and Engineering Center (NSEC) at the University of Massachusetts, Amherst. Professor Watkins received his B.S. and M.S. degrees in Chemical Engineering from the Johns Hopkins University and his Ph.D. in Polymer Science and Engineering from the University of Massachusetts. He joined the Chemical Engineering faculty at UMass in 1996 and the Polymer Science and Engineering Faculty in 2005. Prof. Watkins is a recipient of the Camille Dreyfus Teacher-Scholar Award and a David and Lucile Packard Foundation Fellowship for Science and Engineering. He is a fellow of the American Physical Society.
Invited talk:
Low Cost, Durable Masters for Imprint Lithography and Injection Molding by NIL Patterning of Metal Oxides
Micron-scale and nano-scale patterning of surfaces by imprint lithography, embossing and injection molding are of interest in a broad range of applications including anti-microbial and anti-drag surfaces, structural color, anti-counterfeiting and micro- and nano-fluidics. One challenge, particularly for nanoscale patterning, is the creation of low cost durable masters that can survive tens of thousands and in some case hundreds of thousands of cycles. Typically such masters are created using clean room processing techniques, including optical or e-beam lithography followed by subtractive processing of robust substrates such as Si, quartz and stainless steel. Creation of the masters is not only time consuming, but is also resource and capital intensive, creating barriers to commercialization.
Recently we developed new materials and approaches for direct imprint patterning of crystalline metal oxides for a variety of applications. A polymer master stamp is used to imprint an ink containing high concentrations of crystalline nanoparticles dispersed in solvent and/or sol-gel precursors to a desired inorganic phase. Residual layer free direct imprinting (without etching) is achieved by choosing an ink with the appropriate surface energy to ensure dewetting at stamp-substrate interface. The technique can be further extended to stack the nanostructures by deploying a layer-by-layer imprint strategy. To date, the imprinted metal oxides have been used directly in devices, including optics, microbatteries and wave-length selective thermal emitters. Here we show that imprinting using metal oxide inks can be used to create low cost “daughter molds” that can be subsequently used as masters for imprint lithography, embossing and injection molding.
We created crystalline zirconia daughter molds (that are subsequently used as masters) by imprint patterning of ZrO2 nanoparticle-based inks. In one example we replicated a shark-skin anti-microbial surface pattern in polymers using a ZrO2 master and thermal or UV-assisted nanoimprint lithography. In a second example we replicated a pattern for structural color using a ZrO2 mold insert for injection molding. The ZrO2 master, which contained half-pitch gratings with periods of 700-1400 nm and a feature height of 175 nm, was used for more than 100,000 cycles of ABS molding without loss of pattern fidelity. This paradigm, in which durable zirconia masters for nanoscale polymer replication can be created as inexpensively as the polymer imprints themselves, may have a profound effect on the economics and utility of polymer replication and the nanoscale.