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Enriching libraries of high-aspect-ratio micro- or nanostructures by rapid, low-cost, benchtop nanofabrication

Abstract

We provide a protocol for transforming the structure of an array of high-aspect-ratio (HAR) micro/nanostructures into various new geometries. Polymeric HAR arrays are replicated from a Bosch-etched silicon master pattern by soft lithography. By using various conditions, the original pattern is coated with metal, which acts as an electrode for the electrodeposition of conductive polymers, transforming the original structure into a wide range of user-defined new designs. These include scaled replicas with sub-100-nm-level control of feature sizes and complex 3D shapes such as tapered or bent columnar structures bearing hierarchical features. Gradients of patterns and shapes on a single substrate can also be produced. This benchtop fabrication protocol allows the production of customized libraries of arrays of closed-cell or isolated HAR micro/nanostructures at a very low cost within 1 week, when starting from a silicon master that otherwise would be very expensive and slow to produce using conventional fabrication techniques.

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Figure 1: Overview and comparison of different STEPS methods.
Figure 2: Example SEM images of STEPS-modified structures.
Figure 3: SEM images of fabricated Si masters.
Figure 4: Photos describing the PROCEDURE from Steps 17 to 25.
Figure 5: Photos describing the PROCEDURE from Steps 26 to 35.
Figure 6: Photos of the equipment used for metallization procedures described in Step 36C.
Figure 7: Photos of the electrodeposition setup.
Figure 8: SEM images of microposts metallized for STEPS-II and STEPS-III.
Figure 9: Typical current versus time graphs obtained from a chronoamperometry experiment used for STEPS-I, STEPS-II and STEPS-III.
Figure 10: Typical current versus time graph obtained from a STEPS-IV experiment.

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Acknowledgements

This work was partially supported by the US Department of Energy, Office of Basic Energy Sciences and the Division of Materials Science and Engineering, under award no. DE-SC0005247 (design of HAR structures); the US Army Research Office Multidisciplinary University Research Initiative under award no. W911NF-09-1-0476 (electrodeposition and mechanical properties); and the US Air Force Office of Scientific Research Multidisciplinary University Research Initiative under award no. FA9550-09-1-0669-DOD35CAP (optical properties). This work was carried out in part through the use of the Massachusetts Institute of Technology's Microsystems Technology Laboratories. Part of this work was also performed at the Center for Nanoscale Systems at Harvard University, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (NSF) under NSF award no. ECS-0335765. W.E.A.-M. thanks REU BRIDGE, co-funded by the ASSURE program of the Department of Defense in partnership with the National Science Foundation REU Site program under NSF grant no. DMR-1005022. We thank J.C. Weaver for help in manuscript preparation and E. Macomber for technical assistance with metal deposition equipment.

Author information

Authors and Affiliations

Authors

Contributions

P.K. and J.A. co-invented the STEPS method. J.A. supervised the project and advised on the applications of STEPS. M.K. and P.K. designed the masks. M.K. fabricated the reticles and the Si masters. P.K. and W.E.A.-M. performed replication, metallization and electrochemical deposition experiments and the characterization and analysis of the STEPS-modified structures. P.K., W.E.A.-M., M.K. and J.A. wrote the manuscript.

Corresponding author

Correspondence to Philseok Kim.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

SEM images of a uni-directionally bent nanopost array decorated with PPy nanofibers. (TIFF 11721 kb)

Supplementary Fig. 2

SEM images (taken at 45 degree tilt angle) of gradually reinforced 'Y' shaped columnar arrays using STEPS-II protocol (a-c) and the FEM simulation results showing the induced stress under applied compressive load of 100 MPa (d: original structure, e: reinforced structure). Images are adapted with permission from Kim, P. et al., Nano Letters (DOI:10.1021/nl200426g). Copyright 2011 American Chemical Society. (TIFF 11721 kb)

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Kim, P., Adorno-Martinez, W., Khan, M. et al. Enriching libraries of high-aspect-ratio micro- or nanostructures by rapid, low-cost, benchtop nanofabrication. Nat Protoc 7, 311–327 (2012). https://doi.org/10.1038/nprot.2012.003

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