Print and Shrink: A New Strategy for Printable Electronics?

The attractiveness of printing electronics over more conventional approaches lies in its potential to pattern large-areas and flexible devices inexpensively on plastic substrates.¹ Such technologies could prove critical for such applications as flexible displays and antennas.^2,3 While screen-printing and ink-jet printing are limited in resolution, we provide a means to improve upon the inherent limit of printing resolution by printing on pre-stressed plastic sheets. With a 95% reduction in area, we can achieve high resolution and high aspect ratio structures.

Professor Khine from University of California, Irvine proposed a simple, ultra-rapid, and robust method to create large areas of nanowrinkles as well as sharp high surface area bimetallic nanostructures, coined nanopetals, in a shape memory polymer. By patterning at the large scale, which is easy and inexpensive, we rely on the heat-induced relaxation of pre-stressed shape memory polymer sheets to achieve our desired structures.^4-6

Figure 1. Ultra-rapid, low cost manufacturing process of nanostructures integrated into plastic. Nanowrinkles formed by isoptropic shrinkage (a) by patterning via shadow mask and then shrinking isotropically (b), by shrinking anisotropically (c) and nanopetals created by cracking the nanowrinkles.

The resulting nanostructures -- that serve as effective nano-antennas -- are self-assembled by leveraging the mis-match in stiffness between the retracting pre-stressed polymer sheet and the metallic thin films. These nanopetals provide tiny hot-spots at their edges which exhibit extremely strong plasmonic effects, confining the emission to small excitation volumes (10^-18L) and enhancing the fluorescence intensity of nearby fluorophores by several thousand-folds.

The strong surface plasmon effects of these nanopetals in the vicinity of fluorescein excited by two-photon microscopy exhibit over 4000-fold enhancements in fluorescence intensity. These nanostructures are easily and ultrarapidly created and can be robustly integrated into plastic sheets. With this approach, we can make a variety of structures including high surface area electrodes as well as optical waveguiding structures.

Our previous works with shrink films have focused on the applications of a polystyrene toy called "Shrinky-Dinks".⁷ Recently, we demonstrated that a polyolefin shrink thin film exhibits a 95% reduction in area for high-aspect templates for soft lithography.⁸ By combining with a low-cost digital craft cutter, we were able to also achieve relatively uniform and consistent complete microfluidic channels with smooth surfaces, vertical sidewalls, and high aspect ratio channels with lateral resolutions well beyond the tool used to cut them.⁹ When combined with conductive inks or metals, we can create interesting structures useful for printed nano-electronics.

References

1. B. Y. Ahn, E. B. Duoss, M. J. Motala, X. Guo,S.Park, Y. Xiong, J. Yoon, R. G. Nuzzo, J. A. Rogers, J. A. Lewis, Science, 2009, 323,1590-1592.
2. J. A. Rogers et al., Proc. Natl. Acad. Sci, 2001, 98, 4835.
3. R. A. Potyrailo, W. G. Morris, Anal. Chem., 2007, 79, 45.
4. K. Sollier, C. A. Mandon, K. A. Heyries, L. J. Blum and C. A. Marquette, Lab Chip, 2009, 9, 3489-3494.
5. M. Long, M. A. Sprague, A. A. Grimes, B. D. Rich and M. Khine, Appl Phys Lett, 2009, 94,
6. C. S. Chen, D. N. Breslauer, J. I. Luna, A. Grimes, W. C. Chin, L. P. Leeb and M. Khine, Lab Chip, 2008, 8, 622-624.
7. A. Grimes, D. N. Breslauer, M. Long, J. Pegan, L. P. Lee and M. Khine, Lab Chip, 2008, 8, 170-172.
8. D. Nguyen, D. Taylor, K. Qian, N. Norouzi, J. Rasmussen, S. Botzet, K. H. Lehmann, K. Halverson and M. Khine, Lab Chip , 2010, 10, 1623-1626.
9. D. Taylor, D. Dyer, V. Lew, M. Khine, Lab Chip, 2010, DOI: 10.1039/c0047

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