Optimizing Two-Photon Initiators and Exposure Conditions for Three-Dimensional Lithographic Microfabrication

Stephen M. Kuebler; Mariacristina Rumi; Toshiyuki Watanabe; Kevin Braun; Brian H. Cumpston; Ahmed A. Heikal; Lael L. Erskine; S. Thayumanavan; Stephen Barlow; Seth R. Marder; Joseph W. Perry

doi:10.2494/photopolymer.14.657

Stephen M. Kuebler, Mariacristina Rumi, Toshiyuki Watanabe, Kevin Braun, Brian H. Cumpston, Ahmed A. Heikal, Lael L. Erskine, S. Thayumanavan, Stephen Barlow, Seth R. Marder, Joseph W. Perry

Author information

Stephen M. Kuebler
Department of Chemistry, the University of Arizona
Mariacristina Rumi
Department of Chemistry, the University of Arizona
Toshiyuki Watanabe
Permanent address: Department of Applied Chemistry, Faculty of Technology, Tokyo University of Agriculture & Technology
Kevin Braun
Department of Chemistry, the University of Arizona
Brian H. Cumpston
Department of Chemistry, the University of Arizona
Ahmed A. Heikal
Department of Chemistry, the University of Arizona
Lael L. Erskine
Department of Chemistry, the University of Arizona
S. Thayumanavan
Department of Chemistry, the University of Arizona
Stephen Barlow
Department of Chemistry, the University of Arizona
Seth R. Marder
to whom correspondence should be addressed
Joseph W. Perry
to whom correspondence should be addressed

Keywords: Two-photon induced polymerization, three-dimensional lithographic microfabrication, micro-electromechanical systems, micro-optics, microfluidics, two-photon absorption

JOURNAL FREE ACCESS

2001 Volume 14 Issue 4 Pages 657-668

DOI https://doi.org/10.2494/photopolymer.14.657

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Abstract

The radical photoinitiation characteristics of a range of D-π-D chromophores (where D is an electron-donor and π is a biphenyl, stilbene, or bis(styryl)benzene conjugated bridge) under two-photon excitation are reported. Photo-crosslinkable resins were formulated with these initiators and were used to fabricate a variety of complex three-dimensional structures by two-photon induced polymerization (TPIP). These structures illustrate that TPIP can be a highly versatile technique for the rapid single-step fabrication of complex microstructures and devices. The new two-photon resins were found to be as much as 50 times more sensitive than resins containing conventional UV initiators. The increased two-photon sensitivity is attributed to the large two-photon absorption cross-sections and the efficient electron-transfer mediated initiation of the polymerization by the D-π-D chromophores. A three-dimensional test-structure was used to evaluate how varying the intensity and the exposure times affects the shape and dimensions of the polymerization volume element (voxel). Conditions were found for which the voxel could be as small as -200nm in width and -700nm in length, even though the wavelength of the two-photon excitation radiation was 775nm.

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