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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. In this paper, we conduct systematic computational modeling to investigate the governing mechanisms of the transfer printing process. While the existing understanding of transfer printing mainly relies on the differential interfacial adhesion, our results suggest that both interfacial defects ͑e.g., cracks͒ and differential interfacial adhesion play pivotal roles in the transfer printing quality. 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 for material selection and design strategies to achieve successful transfer printing.

It is well known that a circular hole in a blanket thin film causes strain concentration near the hole edge when the thin film is under tension. The increased strain level can be as high as three times of the applied tension. Interestingly, we show that, by suitably patterning an array of circular holes in a thin film, the resulting strain in the patterned film can be decreased to only a fraction of the applied tension, even at the hole edges. The strain deconcentration in the film originates from the following deformation mechanism: while initially planar, the film patterned with circular holes elongates by deflecting out of plane, so that a large tension induces only small strains. Using finite element simulations, we investigate the effects of geometric parameters (i.e., hole size, spacing, and pattern) and loading direction on the resulting strain in patterned thin films under tension. The large deformability of the patterned film is independent of materials and length scale, and thus sheds light on a potential architecture concept for flexible electronics.

Polymer/oxide nano hybrid multilayer permeation barriers are emerging as a promising solution to the stringent barrier requirement of flexible electronics. Yet the mechanical failure of the multilayer permeation barriers could be fatal to their barrier performance. We study two coevolving failure mechanisms of the multilayer permeation barriers under tension, namely, the cracking of the inorganic oxide layer and the delamination along the oxide-organic interface, using computational modeling. An effective driving force for the oxide layer cracking is determined, which decreases as the oxide-organic interfacial adhesion increases.

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. It emerges as a potential fabrication technique to enable a low-cost and scalable roll-to-roll printing process of flexible devices [1,2], such as paper-like displays, skin-like smart prosthesis and printable thin film solar cells. Although transfer printing has been demonstrated in a wide range of material systems, the quality control of transfer printing has been mainly explored via massive experimental trials, which are both time-consuming and cost-prohibitive, and thus lead to limited understanding. In this paper, we aim to reveal the mechanisms that underpin the quality of transfer printing via a comprehensive computational modeling. The outcome of this study is a quality map of transfer printing, which can offer vital guidance for the structural design, defect control and materials selection of flexible devices to be fabricated via transfer printing. Figure 1 illustrates the two steps of a transfer printing process: (1) A printable layer is sandwiched in between a transfer substrate and a device substrate under pressure and elevated temperature; (2) The structure is cooled and the transfer substrate is lifted off. These two steps can be repeated to achieve multiple layer printing. Various organic and inorganic materials can be transfer printed in the same manner thus avoiding mixed processing methods and allowing multilayer registration. In practice, a transfer printing process can result in successful, unsuccessful, or partial transfer printing of the printable layer onto the device substrate. The understanding of critical transfer printing conditions governing print quality is still preliminary.A successful transfer printing is essentially a well-controlled interfacial delamination process along the interface between the transfer substrate and the printable layer instead of that between the printable layer and the device substrate. Therefore, the initial interfacial defects can have pivotal impacts on the transfer printing quality. To study the effect of initial interfacial defects on the competing delamination in the tri-layer structure of transfer printing, we use the finite element code ABAQUS to simulate the lift-off step of the transfer printing process. We focus on the impact of the initial interfacial cracks at the edges of the two interfaces in the trilayer structure. Figure 2 shows the computational model. During the lift-off, the mechanical separation causes opening displacement of both interfacial edge cracks. The driving force for the interfacial crack at the top interface (or bottom interface) to propagate is quantified by an energy release rate at the crack tip t G (or b G ). If the driving force for the top interfacial crack, t G , is greater than the interfacial adhesion energy between the transfer substrate and the printable layer, c t G , delamination along the top interface occurs. Similarly, if b G is greater t...