Research Highlights

A quality map of tranfer printing

Transfer printing is a nanofabrication technique that involves an assembly process by which a printable layer can be transferred from a transfer substrate to a device substrate. Future application of transfer printing toward a roll-to-roll printing process of flexible devices hinges upon the understanding on the mechanisms governing transfer printing quality, which is far from mature. So far, the quality control of transfer printing has been mainly explored via massive experimental trials, which are both time-consuming and cost-prohibitive. We conduct systematic computational modeling to investigate the underpinning mechanisms of transfer printing process. The outcomes of this study define a quality map of transfer printing in the space spanned by the critical mechanical properties and geometrical parameters in a transfer printing structure. Such a quality map offers new insights and quantitative guidance on the material selection and design strategies to achieve successful transfer printing.

Substrate-regulated morphology of graphene

Graphene's exceptional properties have led to the emergence of a new paradigm of materials science and condensed-matter physics, and have also inspired an array of tantalizing potential applications, ranging from flexible and invisible displays to chemical and biochemical sensing arrays. The future success of graphene-based applications hinges upon precise control of graphene morphology over large areas, a crucial but large unexplored research topic. To address this issue, we delineate a general theoretical framework to determine the substrate-regulated graphene morphology through energy minimization. Our quantitative results envision a promising strategy to precisely control the graphene morphology over large areas via substrate regulation. The rich features of the substrate-regulated graphene morphology (e.g., the snap-through instability) can potentially lead to new design concepts of functional graphene device components.

Mechanics of microtubules buckling in living cells

As the most rigid cytoskeletal filaments, microtubules bear compressive forces in living cells, balancing the tensile forces within the cytoskeleton to maintain the cell shape. Microtubules in living cells often severely buckle into short waves. By contrast, isolated microtubules in vitro buckle into long arcs. We describe a mechanics model to explain this discrepancy.

An architectural concept for flexible electronics

Combining 3D large deformation finite element modeling and experimental analysis, we showed that nanoscale thin films of stiff materials, suitably patterned on sufficiently compliant substrates, can sustain large elongations without fracture. We proposed that such compliant patterns of stiff materials can serve as general platforms for flexible electronic devices. The resulting architecture will function without appreciable fatigue when the substrate is repeatedly bent, twisted, and stretched.

Ductility of thin metal films on polymer substrates

Thin metal films deposited on polymer substrates are often used as conductors in flexible electronics. The deformability of such thin metal films is of particular importance to the reliability of flexible devices under large deformation. While free standing thin metal films suffer from low ductility (~1%), polymer-supported metal films have a large variation of ductility (from 1% to 50%). We study the effects of interfacial adhesion, grain size and grain boundary adhesion on the ductility of polymer-supported thin metal films.