Microfabrication through Self-Ordering of Cracks: Mechanism, Upscaling and Application for Transparent Electrodes

When drying a colloidal solution, cracks appear in the resulting colloidal film. In certain cases, spontaneous order is observed, and cracks form arrays of periodic patterns. Although this phenomenon might be envisioned as a patterning method, overcoming practical challenges is necessary to transform it into a technological tool for microfabrication. This study explores various technological aspects aimed at leveraging the self-assembly of cracks as a scalable microfabrication tool for large-scale device production. Through a series of analyses, including time-resolved Grazing-Incidence Small-Angle X-Ray Scattering (GISAXS), it is offered novel insights into controlling the crack self-ordering mechanism, minimizing defects, and implementing strategies for large-scale patterning and pattern transfer. The process proves to be surprisingly robust, maintaining its efficacy with the same colloidal solution even after two years. By introducing biphasic dip-coating, large-scale crack patterns up to 100 cm², while preserving their periodicity and ordering is achieved. As a proof of concept, the use of crack-patterned colloidal films as masks for fabricating metallic sub-micrometer objects, that serve as transparent electrodes with adjustable transparency and conductivity is showcased. Overall, this method presents significant advantages over conventional lithography, being cost-effective, versatile, environmentally friendly, and scalable, thereby offering new perspectives for diverse applications requiring cost-effective and large-scale patterning.