Low Cost, Durable Masters for Imprint
Lithography and Injection Molding by NIL
Patterning of Metal Oxides
Feyza Dundar, Vince Einck and James J. Watkins
Polymer Science and Engineering Department
Center for Hierarchical Manufacturing
University of Massachusetts
Amherst, MA 01003
Email: watkins@polysci.umass.edu
Alicia Johansson, Ilja Czolkos and Theodor Nielsen
NIL Technology
Diplomvej 381, DK-2800
Kongens Lyngby, Denmark
Email: theo@nilt.com

Micron-scale and nano-scale patterning of surfaces by imprint lithography, embossing andinjection molding are of interest in a broad range of applications including anti-microbial andanti-drag surfaces, structural color, anti-counterfeiting, optical devices, thermal emitters andmicro- 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 ofthousands 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 isalso 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) isachieved by choosing an ink with the appropriate surface energy to ensure dewetting at stampsubstrate interface. The technique can be further extended to stack the nanostructures bydeploying a layer-by-layer imprint strategy. To date, the imprinted metal oxides have been useddirectly 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 “daughtermolds” that can be subsequently used as masters for imprint lithography, embossing andinjection molding.
We created crystalline zirconia daughter molds (that are subsequently used as masters) byimprint patterning of ZrO2 nanoparticle-based inks. In one example we replicated a shark-skinanti-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 aZrO2 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 at the nanoscale.

Figure 1: Images of (a) Si master mold. (b) ZrO2 mold on a Si wafer. (c) PMMA inverse structures of theZrO2 master on a PET substrate.

Figure 2: SEM images of (a) patterned ZrO2 NPs on steel using solvent-assisted soft NIL, (b) higher
magnification with 45o tilt, (c) inverse PMMA structures using hard ZrO2 mold via thermal NIL, and (d)higher magnification. (f) Digital photos of ZrO2 imprint on a curved watch glass (e) Digital photo of ZrO2
master mold on Kapton film. SEM images of (g) patterned metal oxide nanoparticles on Kapton film, (h)and inverse PMMA structures using hard metal oxide mold via thermal NIL.

Reference:[1] Beaulieu, M.R.; Hendricks, N.R.; Watkins, J.J.; “Large-Area Printing of Optical Gratings and
3D Photonic Crystals Using Solution-Processable Nanoparticle/Polymer Composites” ACS
Photonics 2014 1, (9) 799-805.
[2] Arisoy, F. D.; Kolewe, K. W.; Homyak, B.; Kurtz, I. S.; Schi, J. D.; Watkins, J. J. “Bioinspired
Photocatalytic Shark-Skin Surfaces with Antibacterial and Antifouling Activity via Nanoimprint
Lithography” ACS Appl. Mater. Interfaces 2018, 10 (23), 20055–20063.
[3] Li, W.; Zhou, Y.; Howell, I. R.; Gai, Y.; Naik, A. R.; Li, S.; Carter, K. R.; Watkins, J. J. “DirectImprinting of Scalable , High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion
Nanobatteries” ACS Appl. Mater. Interfaces 2018, 10 (6), 5447–5454.
[4] Li, W.; Christiansen, T. L.; Li, C.; Zhou, Y.; Fei, H.; Mamakhel, A.; Iversen, B. B.; Watkins, J. J.
High-Power Lithium-Ion Microbatteries from Imprinted 3D Electrodes of Sub-10 Nm
LiMn2O4/Li4Ti5O12 Nanocrystals and a Copolymer Gel Electrolyte. Nano Energy 2018, 52, 431–440.
[5] Beaulieu, M. R.; Hendricks, N. R.; Watkins, J. J. “Large-Area Printing of Optical Gratings and 3D

Photonic Crystals Using Solution-Processable Nanoparticle/Polymer Composites” ACS Photonics 2014,1 (9), 799–805.