Eric B. Duoss

Omnidirectional printing of flexible, stretchable, and spanning silver microelectrodes.

Flexible, stretchable, and spanning microelectrodes that carry signals from one circuit element to another are needed for many emerging forms of electronic and optoelectronic devices. We have patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks in both uniform and high–aspect ratio motifs with minimum widths of approximately 2 micrometers onto semiconductor, plastic, and glass substrates. The patterned microelectrodes can withstand repeated bending and stretching to large levels of strain with minimal degradation of their electrical properties. With this approach, wire bonding to fragile three-dimensional devices and spanning interconnects for solar cell and light-emitting diode arrays are demonstrated.

Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs

The high natural abundance of silicon, together with its excellent reliability and good efficiency in solar cells, suggest its continued use in production of solar energy, on massive scales, for the foreseeable future. Although organics, nanocrystals, nanowires and other new materials hold significant promise, many opportunities continue to exist for research into unconventional means of exploiting silicon in advanced photovoltaic systems. Here, we describe modules that use large-scale arrays of silicon solar microcells created from bulk wafers and integrated in diverse spatial layouts on foreign substrates by transfer printing. The resulting devices can offer useful features, including high degrees of mechanical flexibility, user-definable transparency and ultrathin-form-factor microconcentrator designs. Detailed studies of the processes for creating and manipulating such microcells, together with theoretical and experimental investigations of the electrical, mechanical and optical characteristics of several types of module that incorporate them, illuminate the key aspects.

Ultralight, ultrastiff mechanical metamaterials

Microlattices make marvelous materials Framework or lattice structures can be remarkably strong despite their very low density. Using a very precise technique known as projection microstereolithography, Zheng et al. fabricated octet microlattices from polymers, metals, and ceramics. The design of the lattices meant that the individual struts making up the materials did not bend under pressure. The materials were therefore exceptionally stiff, strong, and lightweight. Science, this issue p. 1373 Ultralow-density materials that deform through tension or compression rather than bending show much higher stiffness. The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material.

Pen‐on‐Paper Flexible Electronics

Figure 1 . a) Optical image of a rollerball pen loaded with a conductive silver ink. The background shows conductive text written on Xerox paper. b and c) SEM images of the side and top views of the rollerball pen. d) Optical image of the rollerball pen tip, captured during writing a conductive silver track on a Xerox paper. Printed electronics constitute an emerging class of materials with potential application in photovoltaics, [ 1 ] transistors, [ 2 , 3 ] displays, [ 4–6 ] batteries, [ 7 ] antennas, [ 8 ] and sensors. [ 9 , 10 ] Recent attention has focused on paper substrates as a low-cost, enabling platform for fl exible, lightweight, and disposable devices. [ 11–13 ]

Highly compressible 3D periodic graphene aerogel microlattices

Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Youngs moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.

Conformal printing of electrically small antennas on three-dimensional surfaces

J. J. Adams ,[+] Prof. J. T. Bernhard Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801, USA E-mail: jbernhar@illinois.edu Dr. E. B. Duoss ,[+,++] T. F. Malkowski ,[+] Dr. B. Y. Ahn , Prof. J. A. Lewis Department of Materials Science and Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801 USA E-mail: jalewis@illinois.edu Dr. M. J. Motala , Prof. R. G. Nuzzo Department of Chemistry University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA [+] These authors contributed equally to this work. [++] Presently at Lawrence Livermore National Laboratory, Center for Microand NanoTechnology, Livermore, CA 94550 USA

Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores

Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g(-1)) and power densities (>4 kW·kg(-1)) that equal or exceed those of reported devices made with electrodes 10-100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications.

Two- and three-dimensional folding of thin film single-crystalline silicon for photovoltaic power applications

Fabrication of 3D electronic structures in the micrometer-to-millimeter range is extremely challenging due to the inherently 2D nature of most conventional wafer-based fabrication methods. Self-assembly, and the related method of self-folding of planar patterned membranes, provide a promising means to solve this problem. Here, we investigate self-assembly processes driven by wetting interactions to shape the contour of a functional, nonplanar photovoltaic (PV) device. A mechanics model based on the theory of thin plates is developed to identify the critical conditions for self-folding of different 2D geometrical shapes. This strategy is demonstrated for specifically designed millimeter-scale silicon objects, which are self-assembled into spherical, and other 3D shapes and integrated into fully functional light-trapping PV devices. The resulting 3D devices offer a promising way to efficiently harvest solar energy in thin cells using concentrator microarrays that function without active light tracking systems.

Encapsulated liquid sorbents for carbon dioxide capture

Drawbacks of current carbon dioxide capture methods include corrosivity, evaporative losses and fouling. Separating the capture solvent from infrastructure and effluent gases via microencapsulation provides possible solutions to these issues. Here we report carbon capture materials that may enable low-cost and energy-efficient capture of carbon dioxide from flue gas. Polymer microcapsules composed of liquid carbonate cores and highly permeable silicone shells are produced by microfluidic assembly. This motif couples the capacity and selectivity of liquid sorbents with high surface area to facilitate rapid and controlled carbon dioxide uptake and release over repeated cycles. While mass transport across the capsule shell is slightly lower relative to neat liquid sorbents, the surface area enhancement gained via encapsulation provides an order-of-magnitude increase in carbon dioxide absorption rates for a given sorbent mass. The microcapsules are stable under typical industrial operating conditions and may be used in supported packing and fluidized beds for large-scale carbon capture.

Biomimetic silicification of 3D polyamine-rich scaffolds assembled by direct ink writing

We report a method for creating synthetic diatom frustules the biomimetic silicification of polyamine-rich scaffolds assembled by direct ink writing (DIW) [G. M. Gratson, M. Xu and J. A. Lewis, , 2004, , 386, ]. A concentrated polyamine-rich ink is robotically deposited in a complex 3D pattern that mimics the shape of naturally occurring diatom frustules, Ehrenberg (triangular-shaped) and (web-shaped). Upon exposing these scaffolds to silicic acid under ambient conditions, silica formation occurs in a shape-preserving fashion. Our method yields 3D inorganic-organic hybrids structures that may find potential application as templates for photonic materials, novel membranes, or catalyst supports.