Guided fracture of films on soft substrates to create micro/nano-feature arrays with controlled periodicity

Abstract

While the formation of cracks is often stochastic and considered undesirable, controlled fracture would enable rapid and low cost manufacture of micro/nanostructures. Here, we report a propagation-controlled technique to guide fracture of thin films supported on soft substrates to create crack arrays with highly controlled periodicity. Precision crack patterns are obtained by the use of strategically positioned stress-focusing V-notch features under conditions of slow application of strain to a degree where the notch features and intrinsic crack spacing match. This simple but robust approach provides a variety of precisely spaced crack arrays on both flat and curved surfaces. The general principles are applicable to a wide variety of multi-layered materials systems because the method does not require the careful control of defects associated with initiation-controlled approaches. There are also no intrinsic limitations on the area over which such patterning can be performed opening the way for large area micro/nano-manufacturing.

Cracking-assisted photolithography for mixed-scale patterning and nanofluidic applications

“…This is because the single exposed photoresist is more vulnerable to molecular level defects that can act as notches to initiate unwanted cracking, whereas the double exposed photoresist enables the formation of cracking onto the single exposed region only, preventing the occurrence of unwanted cracking. All these characteristics allow the production of nanopatterns that could not be achieved using either conventional techniques showing low throughput and requiring high cost or unconventional techniques depending on a crystallized substance 11 and/or applied anisotropic tensile stresses 4,5,8,9 ( Supplementary Figs 6 and 7).…”

“…However, the nanolithography and/or the combination of the two multi-scale lithography techniques show weaknesses in throughput and cost caused by the direct-writing-based nanofabrication processes and scale-up or scale-down lithography processes in series 2,3 . Cracks are considered material failures and have never been welcome in micro/ nanofabrication processes, but active manipulation of cracking phenomena made it possible to produce various micro and nanoscale patterns, showing remarkable potential for a novel unconventional patterning technique [4][5][6][7][8][9][10][11][12][13][14] . However, the crackingbased micro and nanopatterns show several weaknesses and limitations: only one-dimensional (1D) or limited 2D patterns because of the direction of applied stresses [4][5][6][7][8][9] and the crystallinity of a substrate 11 , respectively; the insufficient controllability of the geometric dimension (for example, width, depth and length) of cracks/patterns caused by the incapability of manipulating the stress strength [6][7][8][10][11][12][13][14] ; low success rates in patterning because of unwanted crack formation 4,9,11 ; low throughput in fabrication because of sequential and multiple fabrication processes 11,14 ; incompatibility with other microfabrication processes [5][6][7]10 and low reproducibility by micromoulding and/or soft lithography [10]…”

“…However, the crackingbased micro and nanopatterns show several weaknesses and limitations: only one-dimensional (1D) or limited 2D patterns because of the direction of applied stresses [4][5][6][7][8][9] and the crystallinity of a substrate 11 , respectively; the insufficient controllability of the geometric dimension (for example, width, depth and length) of cracks/patterns caused by the incapability of manipulating the stress strength [6][7][8][10][11][12][13][14] ; low success rates in patterning because of unwanted crack formation 4,9,11 ; low throughput in fabrication because of sequential and multiple fabrication processes 11,14 ; incompatibility with other microfabrication processes [5][6][7]10 and low reproducibility by micromoulding and/or soft lithography [10][11][12] . The most relevant alternatives for crackingbased patterning appear to partially or individually address the weaknesses and limitations 4,8,9,11 . Therefore, a novel technique that can comprehensively and fully address all the weaknesses The ultraviolet-exposed photoresist consists of an elastic thin layer on a viscoelastic layer on a silicon substrate and exhibits a gradient in cross-linking density along the direction normal to the substrate.…”

The Collapse and Expansion of Liquid-Filled Elastic Channels and Cracks

“…Scanning-electron microscopy and laser confocalmicroscopy have been used to characterize surface cracks [1,4,10]. The results provide some reference for the shape and size of tunneling cracks, but do not reflect the real profiles of liquid-filled nanochannels.…”

“…The fabrication of this type of nanochannel is fairly easy and cost-effective: an array of parallel channels is created by applying tension to a layered structure. This concept has been greatly enhanced by the development of techniques for controlled cracking, in which microfeatures are used to initiate and propagate cracks at desired locations [9,10], so that there are many identical channels on one substrate. After fabrication, the channels can be reversibly opened and closed by the application and relaxation of an applied tensile strain.…”