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Abstract Patchy particles, i.e., colloidal particles whose surface properties have been modified in predetermined patterns, can serve as building blocks for efficient self‐assembly of well‐defined, ordered structures. This paper introduces MicroSphere AutoLithography (µSAL), a scalable lithographic method for production of patchy particles with arbitrary patch motifs. This technique leverages dielectric microspheres as both a lithographic substrate and the illuminating optic, using the fact that when a plane wave of light is refracted through a sphere, it produces a circular patch of high‐intensity illumination on the back hemisphere. Exposing a collection of microspheres to multiple plane waves, every sphere simultaneously projects identical patterns of illuminated patches onto its own surface. Here, µSAL is demonstrated in barium titanate glass (BTG) microspheres that are coated with a thin (≈40 nm) conformal film of poly(dopamine) acting as the photoresist, fixating the optical pattern into a permanent metal structure through light‐induced reduction of silver ions from the liquid suspension. Varying the index of refraction of the BTG spheres and the suspension produces a range of patch sizes and geometries in good agreement with theoretical modeling.
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Microscale Metal Patterning on Any Substrate: Exploring the Potential of Poly(dopamine) Films in High Resolution, High Contrast, Conformal Lithography
We have explored the potential of poly(dopamine) (PDA) thin films as versatile, high resolution conformal photoresists, using catalytic photoreduction of silver ions to micropattern the film. The combination of photosensitivity, biocompatibilty, and straightforward deposition under mild conditions into thin (~45 nm) conformal coatings on nearly any material makes PDA films of interest in lithographic patterning on highly non-planar geometries as well as on soft and biological materials where standard photoresists cannot be used. PDA and poly(norepinephrine) (PNE) films deposited with a standard autoxidation process were investigated along with PDA film deposited with a fast oxidation (FO) technique. Notably, we find that non-specific deposition of silver off the lithographic pattern is strongly suppressed in PNE and nearly absent in FO-PDA films, which makes very high contrast lithography possible. We attribute this to a lower ratio of catechol to quinone moieties in these films compared to standard PDA films. PNE and FO-PDA films exhibit smaller silver grain sizes (<40 nm) compared to standard PDA films, where grains are up to 200 nm in size. We demonstrate laser-scanning lithography patterns at 1.7 \um spatial resolution, near the optical resolution limit of the experiment. Continuous silver films can readily be deposited on PDA, PNE, and FO-PDA with blue (\lambda = 473 nm) and UV-A (375 nm) light, but not with green (515 nm) light. The UV light at lower intensities deposits silver several times faster than the blue light, but also degrades the deposited silver at high light intensities. Silver films deposited in this way reach the percolation threshold at optical doses (at \lambda = 473}nm) in the range of 10-50 kJ/cm^2 and SEM images of the films appear nearly pinhole free at comparable doses.
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- Award ID(s):
- 1905527
- PAR ID:
- 10598805
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- ACS Applied Materials & Interfaces
- Volume:
- 16
- Issue:
- 48
- ISSN:
- 1944-8244
- Page Range / eLocation ID:
- 66387 to 66401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acsami.4c07115
