Improved Pattern Transfer in Soft Lithography Using Composite Stamps

Odom, Teri W.; Love, J. Christopher; Wolfe, Daniel B.; Paul, Kateri E.; Whitesides, George M.

doi:10.1021/la020169l

Cited by 711 publications

(697 citation statements)

References 13 publications

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“…As shown in Figure 4i, the submicrowires collapse into an entangled mat due to the low elastic modulus of PDMS, 39 resulting in a hierarchical structure with bundled submicrowires. This architecture with dual-scale roughness has been expected to increase the contact angles.…”

Section: Resultsmentioning

confidence: 99%

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Yang

Huang

Lin

et al. 2014

ACS Appl. Mater. Interfaces

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Aluminum (Al) anodization leads to formation of porous structures with a broad spectrum of applications. Naturally or intentionally created defects on Al surfaces can greatly affect pore initiation. However, there is still a lack of systematic understanding on the defect dependent morphology evolution. In this paper, anodization processes on unpolished, polished, and nanoimprinted Al substrates are investigated under high voltages up to 600 V in various acid solutions. A porous structure is obtained on the unpolished and nanoimprinted Al foils with rough surface texture, whereas a compact film can be rationally obtained on the polished Al foil with a highly smooth surface. The observation of surface roughness dependent oxide film morphology evolution could be originated from the high voltages, which increases the threshold requirement of defect size or density for the pore initiation. Electrostatics simulation results indicate that inhomogeneous electric field and its corresponding localized high current induced by the surface roughness facilitate the initiation of nanopores. In addition, the porous films are utilized as templates to produce polydimethylsiloxane nanocone and submicrowire arrays. The nanoarrays with different aspect ratios present tunable wettability with the contact angles ranging from 144.6°to 56.7°, which hold promising potentials in microfluidic devices and self-cleaning coatings.

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Section: Resultsmentioning

confidence: 99%

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Yang

Huang

Lin

et al. 2014

ACS Appl. Mater. Interfaces

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“…23 A 1-mm-thick layer of PDMS (Sylgard 184) was subsequently coated over the PMMA and cured at room temperature ( Figure 1c). This PDMS layer provides the backing layer for the mold so that it can be more easily manipulated, has the flexibility it needs to conform well to substrates, 11,12 and at the same time adds permeability to the solvent used for embossing. The composite mold of PMMA/ PDMS was retrieved by wet etching methods (Figure 1d), first by etching in a 1.4 wt % FeCl 3 in 4 M HCl solution to remove the remaining aluminum beneath the AAO and then subsequently with a 10 wt % NaOH solution to remove the alumina.…”

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confidence: 99%

Nanostructuring Titania by Embossing with Polymer Molds Made from Anodic Alumina Templates

2005

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We demonstrate a method for embossing titania sol−gel precursor with poly(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35−65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol−gel molding. We show that the high modulus of PMMA is necessary to preserve small features with high aspect ratios on the mold for nanopatterning. The molds are prepared by thermally infiltrating PMMA into anodic alumina templates, whose pore dimensions and depths are adjustable by varying anodization conditions. The difficulties associated with mold release from a master are avoided by wet etching the template. These titania films, and others made with other semiconductors, could be useful for photovoltaic, photocatalytic, and sensing applications where nanostructuring of surfaces with controlled dimensions are essential.Nanostructured semiconductor materials have drawn a lot of attention because they exhibit interesting optical, electronic, and catalytic properties. Semiconductor films with a dense array of pores at the 10-50 nm length scale are attractive for photovoltaics, 1-4 photocatalytics, 5,6 and sensing applications. 7 For these applications, it is desirable to pattern semiconductors in a relatively simple and cheap process. Although soft lithography 8 and nanoimprint lithography 9 are promising ways to nanopattern materials, they both have limitations and may not be suitable for patterning certain materials and specifications. Soft lithography, which usually utilizes elastomer poly(dimethylsiloxane) (PDMS) molds, has been extensively used to pattern photoresists, biological macromolecules, and semiconducting polymers. 8,10 The resolution achievable with PDMS however has often been limited to >100 nm due to its relatively low compression modulus of ∼2 MPa. 11 The use of a harder version of PDMS (h-PDMS) with a compression modulus of ∼9 MPa has increased the resolution to about 50 nm, 11,12 but only for features that are not densely spaced together and of high aspect ratio. This points to the need for an even harder mold as patterning is pushed toward increasingly smaller scale. Nanoimprint lithography, which has formidable resolution approaching 5 nm, 13 uses a hard Si or SiO 2 mold to achieve high aspect ratio features. Nanoimprinted materials include photoresists, polymers, silicon, and sol-gel materials, 9,14-16 but some other materials cannot be patterned by nanoimprint lithography because the mold adheres to the film and cannot be removed. For instance, nanostructuring of sol-gel inorganics potentially useful in many low cost applications can be very challenging with either soft lithography or nanoimprint lithography. Here, we demonstrate molding of solgel precursors to make nanostructured metal oxide films, whose features are 1 order of magnitude smaller than those previously demonstrated for sol-gel molding. 15,17 We show that embossing with a hard polymer mold can be an attractive alternative to pattern nanoporo...

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“…The development of harder material formulations providing a higher elastic modulus than Sylgard 184, such as h-PDMS [30,[32][33][34] or photocurable siloxanes [35] proved useful to overcome these constraints to a large extent. Surface tension and residual stress can lead to the appearance of pull-off effects during contact (Figure 122.2e) and the rounding of features that were originally designed to be sharp (Figure 122.2f).…”

Section: Introductionmentioning

confidence: 99%

Sub-Micrometer Patterning Using Soft Lithography

Geißler

2011

Comprehensive Nanoscience and Technology

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Improved Pattern Transfer in Soft Lithography Using Composite Stamps

Cited by 711 publications

References 13 publications

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Nanostructuring Titania by Embossing with Polymer Molds Made from Anodic Alumina Templates

Sub-Micrometer Patterning Using Soft Lithography

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