The cost, form, and performance of the device are limited by the conditions necessary for these processing techniques. For example, conventional photolithography typically requires patterned light to generate user-defined microscale patterns. [3][4][5] More sophisticated techniques such as electron-beam lithography or dip-pen lithography can pattern nanoscale features, but these multistep scanning processes are highcost and labor-intensive. [6,7] Thus, fabrication techniques that can produce highly organized patterns or structures at small size scales with a simple process may offer significant advantages.In synthetic systems, cracking is normally an unwelcomed, uncontrollable, and chaotic phenomenon caused by mechanical conditions that induce material failure. However, living systems, such as the skin of crocodiles and elephants, often show examples of self-organized crack patterns caused by intrinsic anisotropy. [8,9] Inspired by nature, recent advances in crack-assisted fabrication techniques, also referred to as cracklithography, have demonstrated how the humble crack can be Cracks are typically associated with the failure of materials. However, cracks can also be used to create periodic patterns on the surfaces of materials, as observed in the skin of crocodiles and elephants. In synthetic materials, surface patterns are critical to micro-and nanoscale fabrication processes. Here, a strategy is presented that enables freely programmable patterns of cracks on the surface of a polymer and then uses these cracks to pattern other materials. Cracks form during deposition of a thin film metal on a liquid crystal polymer network (LCN) and follow the spatially patterned molecular order of the polymer. These patterned sub-micrometer scale cracks have an order parameter of 0.98 ± 0.02 and form readily over centimeter-scale areas on the flexible substrates. The patterning of the LCN enables cracks that turn corners, spiral azimuthally, or radiate from a point. Conductive inks can be filled into these oriented cracks, resulting in flexible, anisotropic, and transparent conductors. This materials-based processing approach to patterning cracks enables unprecedented control of the orientation, length, width, and depth of the cracks without costly lithography methods. This approach promises new architectures of electronics, sensors, fluidics, optics, and other devices with micro-and nanoscale features.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202008434.
IntroductionProcesses that allow patterning of materials at the micro-or nanoscale enable many devices, including active electronics,
