observation of high-aspect-ratio nanostructures using capillary lithography, by k. y. suh, s.-j....
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Observation of High-Aspect-Ratio Nanostructures Using Capillary Lithography
,by K. Y. Suh, S.-J. Choi, S. J. Baek, T. W. Kim, and R. Langer, Adv. Mater. 2005, 17, No. 5, March 8
AgendaPeriodic nanostructureCapillary lithographyResults
Nanostructure for 300 nm High Mold for Different Film Thickness
Nanostructure for 500 nm High Mold for Different Film Thickness
Nanostructure for 450 nm High Mold for Different Polymer
Conclusion
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Periodic NanostructurePotential application
Photonic crystalsData storageNanometer-scale
biological sensor
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Photonic crystals, from S. M. Yang, G. A. Ozin, Chem. Commun. 2000, 2507
Data storage, from Y.-W. Chen, Y.-H. Tang, L.-Z Pei, and C. Guo,Adv. Mater 2005, 17, No. 5, March 8
Nanometer-scale biological sensor, from K.-B. Lee, S.-J. Park, C.-A. Mirkin, J. C. Smith, and M. Mrksich, Science 2002, 295, 1702.
Capillary Lithography (I)Temperature-Induced Capillarity
Solvent-Induced Capillarity
A small gap is present between the mold and the polymer.
No gap is present since the solvent wet the entire mold surface.
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Place the mold on the polymer surface
Heating
Cooling and mold remove
Slight pressing
Solvent evaporate
Remove the model
Solvent polymer
Mold
Capillary Lithography (II)Material for capillary
lithography Mold
Polyurethane acrylate Polymer
Poly(ethylene glycol)-based (PEG-based) random copolymer
Capillary rise is not expected but happens. It provides several unexpected nanostructure as a result of gas permeation and different wetting condition.
Permeability issue comes into play in the case of the polyurethane acrylate mold, especially when solvent-induced capillary was utilized.
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Capillary Lithography (III)Depending on the
etching conditions of the original silicon master, the height of the voids of the mode could be controlled.
The voids are of a truncated cone shape, with dimensions of 150-200 nm at the base and 70-100 nm at the top.
a) SEM images of the positive mold with step heights of 300 nm.
b) SEM images of the positive mold with step heights of 500 nm.
c) SEM image of the replicated negative mold.
d) An example of the sheet-type polyurethane acrylate mold.
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Nanostructure for 300 nm High Mold for Different Film ThicknessThe max height of the
structure is (2/3) of the mold height. Be achieved by
Maintain conformal contact over the entire surface without many trapped bubbles To avoid air trapped in the
voids to escape Air permeability of the
mode is very small No air escape through the
mode The solubility of air in the
polymer solution is smaller Valid for the water is the
solvent
Two different nanostructures Nanopillar has an average height of
300 nm (for thin films < 500 nm). Nanosphere has an average height of
170-200 nm (for thick films >800 nm).
• SEM images of the two types of nanostructures formed when the mold with a step height of 300 nm is used. a) Formation of nanopillars of reduced diameter. A dimple next to a nanopillar is indicated by an arrow in the inset. b) Formation of anao-hemispheres. Some hemisphere that are peeled off a shown as voids in the inset.
dimple
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Peel off
Nanostructure for 500 nm High Mold for Different Film Thickness (I) Thin film forms mushroom-like nanopillar
Mushroom-like nanopillar A structure in which the head is larger than the body. Caused by the polymer solution wets the adjacent dry region in the mold void
after reaching the ceiling. The orientation varies for each nanopillar because of different wetting path
Has a reduced diameter. Dimples are formed next the nanopillar
A schematic illustration for the formation of the two kinds of nanostructure, depending on wetting condition
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Nanostructure for 500 nm High Mold for Different Film Thickness (II) Thin film forms mushroom-like
nanopillar Mushroom-like nanopillar Has a reduced diameter. Dimples are formed next the
nanopillar. Thick film forms nanospheres
The diameter of the sphere is 150-170 nm.
The spaces between nanospheres is 500 nm.
Agrees with the mold.
SEM images of the two types of nanostructure formed using the mold with a step height of 500 nm. a, c) Formation of mushroom-like nanopillar with a reduced diameter; large-scale (a) and magnified (c) view are shown. A dimple next to a nanopillar is indicated by an arrow in (c). b, d) Formation of nanospheres; larger scale (b) and magnified (d) views are shown.
dimple
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Nanostructure for 450 nm High Mold for Different Polymer (II)Use 450 nm high mold with different polymer to form
nanopillar SPS has a reduced 90 nm diameter PEG has a reduced 110 nm diameter The formation of vertical sidewalls is quite reproducible. The black spots next to the pillars in the figures are dimples
formed by pressure buildup.
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SEM images of well-defined, high-aspect-ratio nanopillars using a) SPS and b) PEG copolymer. The diameters at the base are 90 nm and 110 nm, respectively.
ConclusionPresent the observation of several nanostructures, such
as mushroom-like nanopillars, vertical nanopillars, and nanospheres, using capillary lithography with UV-curable, polyurethane acrylate mold.
Air permeation during capillary plays an important role in pattern replication.
Depends on the thickness of the film, a nanopillar or nanosphere will be produced.
The step height of the mold could be adjusted to obtain well-defined vertical nanopillars less than the step height of mold.
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