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Review
. 2014 Sep 21;14(18):3475-88.
doi: 10.1039/c4lc00528g. Epub 2014 Jul 30.

Thermally-induced miniaturization for micro- and nanofabrication: progress and updates

Sophia Lin  1 , Eugene K Lee, Nancy Nguyen, Michelle Khine
Affiliations
Review

Thermally-induced miniaturization for micro- and nanofabrication: progress and updates

Sophia Lin et al. Lab Chip. .

Abstract

The field of micro- and nanofabrication has developed extensively in the past several decades with rising interest in alternative fabrication techniques. Growth of these areas has been driven by needs that remain unaddressed by traditional lithographical methods: inexpensive, upscalable, biocompatible, and easily integrated into complete lab-on-a-chip (LOC) systems. Shape memory polymers (SMPs) have been explored as an alternative substrate. This review first focuses on structure fabrication at the micron and nanoscale using specifically heat-shrinkable SMPs and highlights the innovative improvements to this technology in the past several years. The second part of the review illustrates demonstrated applications of these micro- and nanostructures fabricated from heat-shrinkable SMP films. The review concludes with a discussion about future prospects of heat-shrinkable SMP structures for integration into LOC systems.

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Figures

Fig 1.
Fig 1.
Schematic illustrating techniques for micro- and nanofabrication using the heat-shrinkable SMP film and current existing applications of the resulting features covered in this review.
Fig 2.
Fig 2.
a) Incorporation of hot-embossing techniques with shrink technology results in reduced feature sizes. SEM images of b) the metal mold and c) the 21 nm line. d) AFM image of the 21 nm line. Adapted from B. Zhang, M. Zhang and T. H. Cui, Appl Phys Lett, 2012, 100 with permission from AIP Publishing.
Fig 3.
Fig 3.
Micro- and nanofabrication on heat-shrinkable SMP film via surface wrinkling. a) Scheme of fabrication of biaxial (left) and uniaxial (right) wrinkles on polystyrene sheets. SEM images of resulting b) biaxial and c) uniaxial wrinkles using gold. Adapted from C. C. Fu, A. Grimes, M. Long, C. G. L. Ferri, B. D. Rich, S. Ghosh, S. Ghosh, L. P. Lee, A. Gopinathan and M. Khine, Adv Mater, 2009, 21, 4472-+ with permission from John Wiley and Sons.
Fig 4.
Fig 4.
Characteristic wavelengths of PS films tuned by changing the RIE exposure time. SEM images of 2D nanowrinkles formed by RIE with CHF3 and times of a) 5 s (λ = 34 nm), b) 10 s (λ = 44 nm), c) 20 s (λ = 107 nm), d) 30 s (λ = 162 nm), e) 40 s (λ = 198 nm), f) 50 s (λ = 228 nm), g) 60 s (λ = 303 nm), h) 70 s (λ = 360 nm), and i) 80 s (λ = 431 nm). Adapted with permission from M. D. Huntington, C. J. Engel, A. J. Hryn and T. W. Odom, Acs Appl Mater Inter, 2013, 5, 6438–6442. Copyright 2013 American Chemical Society.
Fig 5.
Fig 5.
Schematic showing the fabrication procedure of PS channels containing sidewall and bottom patterns. a) shallow, wide channels are etched inside the PS film using a mask; b) removal of the mask reveals channels; c) Ag micropatterns are produced on the substrate using another mask; and d) after strain recovery of the PS block, the Ag micropatterns are transferred to the channel sidewalls. e) 3D visualizations of resulting PS channels covered with Ag microlines and microdots. Adapted from A. Chakraborty, X. C. Liu and C. Luo, Sensor Actuat a-Phys, 2012, 188, 374–382 with permission from Elselvier.
Fig 6.
Fig 6.
Comparing alignment of hESC-CMs on control surfaces to the wrinkle patterned substrates. a) SEM images of the three types of substrates at 1000x magnification (top panel). Fluorescent images of f-actin (red) in hESC-CMs seeded on the various topographies. Nuclei of hESC-CMs were stained with DAPI (blue) (middle panel). Fluorescent images of α-actinin (green) in hESC-CMs seeded on the various topographies. Nuclei of hESC-CMs were stained with DAPI (blue) (bottom panel). b) Percentage of f-actin aligned to the direction of the line/wrinkles (left panel). Measurement of sarcomere alignment efficiency using the orientation organization parameter (right panel). Adapted from A. Chen, E. Lee, R. Tu, K. Santiago, A. Grosberg, C. Fowlkes and M. Khine, Biomaterials, 2014, 35, 675–683 with permission from Elselvier.
Fig. 7
Fig. 7
Shrunk ECL sensor with optical read out methods. a) Wrinkled Au thin film electrodes with samples on patterned detection zones. b) Luminescent images from the CMOS sensor. c) 3D intensity profile of detection zones. Adapted from J. D. Pegan, A. Y. Ho, M. Bachman and M. Khine, Lab Chip, 2013, 13, 4205–4209 with permission from the Royal Society of Chemistry.
Fig. 8
Fig. 8
Shrinkage of nanoporous thin films result in nanostructures for SERS effects. SEM images of a) flat nanoporous films and b) features arising from shrinking nanoporous thin films. c) Chemical composition of the thin films. d) SEM image showing nanogaps hot spots for SERS effects. Adapted from H. W. Liu, L. Zhang, X. Y. Lang, Y. Yamaguchi, H. S. Iwasaki, Y. S. Inouye, Q. K. Xue and M. W. Chen, Sci Rep-Uk, 2011, 1 with permission from Nature Publishing Group.
Fig 9.
Fig 9.
Schematic diagram of DSSCs with shrink induced wrinkles and nanogaps on the photocathodes. a) Fabrication process of shrink-induced wrinkles and nanogaps. The shrink polymer substrate with wrinkles and nanogaps generated on the top surface serves as the photocathode. b) DSSC incorporation with shrink-induced structures. c) Shrink-induced wrinkles and nanogaps on photocathodes enhance the incident light scattering and Pt catalytic area. Adapted from B. Zhang, M. Zhang, K. P. Song, Q. Li and T. H. Cui, Appl Phys Lett, 2013, 103 with permission from AIP Publishing.
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