Patterning by controlled cracking

Abstract

Crack formation drives material failure and is often regarded as a process to be avoided. However, closer examination of cracking phenomena has revealed exquisitely intricate patterns such as spirals, oscillating and branched fracture paths and fractal geometries. Here we demonstrate the controlled initiation, propagation and termination of a variety of channelled crack patterns in a film/substrate system comprising a silicon nitride thin film deposited on a silicon substrate using low-pressure chemical vapour deposition. Micro-notches etched into the silicon substrate concentrated stress for crack initiation, which occurred spontaneously during deposition of the silicon nitride layer. We reproducibly created three distinct crack morphologies--straight, oscillatory and orderly bifurcated (stitchlike)--through careful selection of processing conditions and parameters. We induced direction changes by changing the system parameters, and we terminated propagation at pre-formed multi-step crack stops. We believe that our patterning technique presents new opportunities in nanofabrication and offers a starting point for atomic-scale pattern formation, which would be difficult even with current state-of-the-art nanofabrication methodologies.

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.…”

Localization of Folds and Cracks in Thin Metal Films Coated on Flexible Elastomer Foams

“…The sheet forms wrinkles under compressive stress [1][2][3][4] and forms cracks under tensile stress. [5][6][7] Self-organized patterns of folds and cracks have been exploited in a number of applications, including nano/microfabrication, [ 8 ] surface and interface science, [ 9 , 10 ] biotechnology, [ 11 ] photonics [ 12 ] and stretchable electronics. [ 13 , 14 ] Here, we report on a thin metal fi lm coated on a microcellular elastomer foam.…”

Self-Replicating Cracks: A Collaborative Fracture Mode in Thin Films

“…The patterns form spontaneously along a path determined completely by the geometry of the initiation spot independently from inhomogeneities of adhesion properties (often difficult to control perfectly). Recently developed micropatterning techniques allow the control of the geometry of initiation [25]. Our study provides the operating conditions for these robust patterns through a physical description of the phenomenon supported by numerical and experimental tests.…”