Showing papers by "Yihui Zhang published in 2015"

Assembly of micro/nanomaterials into complex, three-dimensional architectures by compressive buckling

Abstract: Complex three-dimensional (3D) structures in biology (e.g., cytoskeletal webs, neural circuits, and vasculature networks) form naturally to provide essential functions in even the most basic forms of life. Compelling opportunities exist for analogous 3D architectures in human-made devices, but design options are constrained by existing capabilities in materials growth and assembly. We report routes to previously inaccessible classes of 3D constructs in advanced materials, including device-grade silicon. The schemes involve geometric transformation of 2D micro/nanostructures into extended 3D layouts by compressive buckling. Demonstrations include experimental and theoretical studies of more than 40 representative geometries, from single and multiple helices, toroids, and conical spirals to structures that resemble spherical baskets, cuboid cages, starbursts, flowers, scaffolds, fences, and frameworks, each with single- and/or multiple-level configurations.

A mechanically driven form of Kirigami as a route to 3D mesostructures in micro/nanomembranes.

Abstract: Assembly of 3D micro/nanostructures in advanced functional materials has important implications across broad areas of technology. Existing approaches are compatible, however, only with narrow classes of materials and/or 3D geometries. This paper introduces ideas for a form of Kirigami that allows precise, mechanically driven assembly of 3D mesostructures of diverse materials from 2D micro/nanomembranes with strategically designed geometries and patterns of cuts. Theoretical and experimental studies demonstrate applicability of the methods across length scales from macro to nano, in materials ranging from monocrystalline silicon to plastic, with levels of topographical complexity that significantly exceed those that can be achieved using other approaches. A broad set of examples includes 3D silicon mesostructures and hybrid nanomembrane–nanoribbon systems, including heterogeneous combinations with polymers and metals, with critical dimensions that range from 100 nm to 30 mm. A 3D mechanically tunable optical transmission window provides an application example of this Kirigami process, enabled by theoretically guided design.

Soft network composite materials with deterministic and bio-inspired designs.

Abstract: Hard and soft structural composites found in biology provide inspiration for the design of advanced synthetic materials. Many examples of bio-inspired hard materials can be found in the literature; far less attention has been devoted to soft systems. Here we introduce deterministic routes to low-modulus thin film materials with stress/strain responses that can be tailored precisely to match the non-linear properties of biological tissues, with application opportunities that range from soft biomedical devices to constructs for tissue engineering. The approach combines a low-modulus matrix with an open, stretchable network as a structural reinforcement that can yield classes of composites with a wide range of desired mechanical responses, including anisotropic, spatially heterogeneous, hierarchical and self-similar designs. Demonstrative application examples in thin, skin-mounted electrophysiological sensors with mechanics precisely matched to the human epidermis and in soft, hydrogel-based vehicles for triggered drug release suggest their broad potential uses in biomedical devices.

Mechanics of stretchable batteries and supercapacitors

Abstract: The last decade has witnessed fast developments and substantial achievements that have been shaping the field of stretchable electronics. Due to a persistent need of equally stretchable power sources, especially for some emerging bio-integrated applications enabled by this unusual class of electronics, stretchable energy storage systems have been attracting increasing attentions in the past few years. This article reviews the mechanics of stretchable batteries and supercapacitors that are enabled by novel structural designs of hard and soft components, involving four representative strategies (i.e., wavy, wrinkled design, origami design, serpentine bridge-island design, and fractal inspired bridge-island design). The key mechanics of each strategy is summarized, with focuses on the design concepts, unique mechanical behaviors, and analytical/computational models that guide the design optimization. Finally, some perspectives are provided on the remaining challenges and opportunities for future research.

Optics and Nonlinear Buckling Mechanics in Large-Area, Highly Stretchable Arrays of Plasmonic Nanostructures.

Abstract: Large-scale, dense arrays of plasmonic nanodisks on low-modulus, high-elongation elastomeric substrates represent a class of tunable optical systems, with reversible ability to shift key optical resonances over a range of nearly 600 nm at near-infrared wavelengths. At the most extreme levels of mechanical deformation (strains >100%), nonlinear buckling processes transform initially planar arrays into three-dimensional configurations, in which the nanodisks rotate out of the plane to form linear arrays with "wavy" geometries. Analytical, finite-element, and finite-difference time-domain models capture not only the physics of these buckling processes, including all of the observed modes, but also the quantitative effects of these deformations on the plasmonic responses. The results have relevance to mechanically tunable optical systems, particularly to soft optical sensors that integrate on or in the human body.

Lateral buckling and mechanical stretchability of fractal interconnects partially bonded onto an elastomeric substrate

Abstract: Fractal-inspired designs for interconnects that join rigid, functional devices can ensure mechanical integrity in stretchable electronic systems under extreme deformations. The bonding configuration of such interconnects with the elastomer substrate is crucial to the resulting deformation modes, and therefore the stretchability of the entire system. In this study, both theoretical and experimental analyses are performed for postbuckling of fractal serpentine interconnects partially bonded to the substrate. The deformation behaviors and the elastic stretchability of such systems are systematically explored, and compared to counterparts that are not bonded at all to the substrate.

Materials and Wireless Microfluidic Systems for Electronics Capable of Chemical Dissolution on Demand

Abstract: Electronics that are capable of destroying themselves, on demand and in a harmless way, might provide the ultimate form of data security. This paper presents materials and device architectures for triggered destruction of conventional microelectronic systems by means of microfl uidic chemical etching of the constituent materials, including silicon, silicon dioxide, and metals (e.g., aluminum). Demonstrations in an array of home-built metal-oxide-semiconductor fi eld-effect transistors that exploit ultrathin sheets of monocrystalline silicon and in radio-frequency identifi cation devices illustrate the utility of the approaches.

A theoretical model of reversible adhesion in shape memory surface relief structures and its application in transfer printing

Abstract: Transfer printing is an important and versatile tool for deterministic assembly and integration of micro/nanomaterials on unusual substrates, with promising applications in fabrication of stretchable and flexible electronics. The shape memory polymers (SMP) with triangular surface relief structures are introduced to achieve large, reversible adhesion, thereby with potential applications in temperature-controlled transfer printing. An analytic model is established, and it identifies two mechanisms to increase the adhesion: (1) transition of contact mode from the triangular to trapezoidal configurations, and (2) explicit enhancement in the contact area. The surface relief structures are optimized to achieve reversible adhesion and transfer printing. The theoretical model and results presented can be exploited as design guidelines for future applications of SMP in reversible adhesion and stretchable electronics.

Analyses of postbuckling in stretchable arrays of nanostructures for wide-band tunable plasmonics

Abstract: Plasmonic nanostructures integrated with soft, elastomeric substrates provide an unusual platform with capabilities in mechanical tuning of key optical properties, where the surface configurations can undergo large, nonlinear transformations. Arrays of planar plasmonic nanodiscs in this context can, for example, transform into three-dimensional (3D) layouts upon application of large levels of stretching to the substrate, thereby creating unique opportunities in wide-band tunable optics and photonic sensors. In this paper, a theoretical model is developed for a plasmonic system that consists of discrete nanodiscs on an elastomeric substrate, establishing the relation between the postbuckling configurations and the applied strain. Analytic solutions of the amplitude and wavelength during postbuckling are obtained for different buckling modes, which agree well with the results of finite-element analyses and experiment measurements. Further analyses show that increasing the nanodisc distribution yields increased 3D configurations with larger amplitudes and smaller wavelengths, given the same level of stretching. This study could serve as a design reference for future optimization of mechanically tunable plasmonic systems in similar layouts.