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Nanomaterials 2018, 8(7), 498;

Deformation Behavior of Foam Laser Targets Fabricated by Two-Photon Polymerization

Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511, USA
Material Science Solutions, 2136 Westbrook Lane, Livermore, CA 94550, USA
Schafer Livermore Lab, 303 Lindbergh Avenue, Livermore, CA 94551, USA
Author to whom correspondence should be addressed.
Received: 31 May 2018 / Revised: 29 June 2018 / Accepted: 3 July 2018 / Published: 6 July 2018
(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)
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Two-photon polymerization (2PP), which is a three-dimensional micro/nano-scale additive manufacturing process, is used to fabricate component for small custom experimental packages (“targets”) to support laser-driven, high-energy-density physics research. Of particular interest is the use of 2PP to deterministically print millimeter-scale, low-density, and low atomic number (CHO) polymer matrices (“foams”). Deformation during development and drying of the foam structures remains a challenge when using certain commercial acrylic photo-resins. Acrylic resins were chosen in order to meet the low atomic number requirement for the foam; that requirement precludes the use of low-shrinkage organic/inorganic hybrid resins. Here, we compare the use of acrylic resins IP-S and IP-Dip. Infrared and Raman spectroscopy are used to quantify the extent of the polymerization during 2PP vs. UV curing. The mechanical strength of beam and foam structures is examined, particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage is quantified, and finite element analysis is used in order to simulate the resulting deformation. Capillary drying forces during development are shown to be small and are likely below the elastic limit of the foam log-pile structures. In contrast, the substantial shrinkage in IP-Dip (~5–10%) causes large shear stresses and associated plastic deformation, particularly near constrained boundaries and locations with sharp density transitions. Use of IP-S with an improved writing procedure results in a marked reduction in deformation with a minor loss of resolution. View Full-Text
Keywords: two-photon polymerization; low-density foam structures; laser targets; structure deformation; acrylate resin; Raman microspectroscopy two-photon polymerization; low-density foam structures; laser targets; structure deformation; acrylate resin; Raman microspectroscopy

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Liu, Y.; Campbell, J.H.; Stein, O.; Jiang, L.; Hund, J.; Lu, Y. Deformation Behavior of Foam Laser Targets Fabricated by Two-Photon Polymerization. Nanomaterials 2018, 8, 498.

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