Zhuang Xie

Three-dimensional compressible and stretchable conductive composites.

Three-dimensional (3D) conductive composites with remarkable flexibility, compressibility, and stretchability are fabricated by solution deposition of thin metal coatings on chemically modified, macroscopically continuous, 3D polyurethane sponges, followed by infiltration of the metallic sponges with polydimethylsiloxane (PDMS). These low-cost conductive composites are used as high-performance interconnects for flexible and stretchable light-emitting diode (LED) arrays, even with severe surface abrasion or cutting.

Matrix‐Assisted Catalytic Printing for the Fabrication of Multiscale, Flexible, Foldable, and Stretchable Metal Conductors

Matrix-assisted catalytic printing (MACP) is developed as a low-cost and versatile printing method for the fabrication of multiscale metal conductors on a wide variety of plastic, elastomeric, and textile substrates. Highly conductive Cu interconnects (2.0 × 10⁸ S/m) fabricated by MACP at room temperature display excellent flexibility, foldability, and stretchability.

Polyelemental nanoparticle libraries.

Multimetal nanoparticle synthesis Multicomponent nanoparticles can be difficult to synthesize. Rather than mixing in one type of particle, the compounds often separate and form distinct particles. Using dip-pen lithography, Chen et al. show how adding reactants to very small volumes forces the reactants to form single particles containing various combinations of five different transition metal ions. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed the shapes of the nanoparticles and how metallic composition varied within them. For example, the quinary particle containing gold, silver, cobalt, copper, and nickel consisted of three domains of binary alloys. Science, this issue p. 1565 Nanoparticles of every combination of five metallic elements were synthesized by means of polymer nanoreactor–mediated synthesis. Multimetallic nanoparticles are useful in many fields, yet there are no effective strategies for synthesizing libraries of such structures, in which architectures can be explored in a systematic and site-specific manner. The absence of these capabilities precludes the possibility of comprehensively exploring such systems. We present systematic studies of individual polyelemental particle systems, in which composition and size can be independently controlled and structure formation (alloy versus phase-separated state) can be understood. We made libraries consisting of every combination of five metallic elements (Au, Ag, Co, Cu, and Ni) through polymer nanoreactor–mediated synthesis. Important insight into the factors that lead to alloy formation and phase segregation at the nanoscale were obtained, and routes to libraries of nanostructures that cannot be made by conventional methods were developed.

Salt-assisted direct exfoliation of graphite into high-quality, large-size, few-layer graphene sheets

We report a facile and low-cost method to directly exfoliate graphite powders into large-size, high-quality, and solution-dispersible few-layer graphene sheets. In this method, aqueous mixtures of graphite and inorganic salts such as NaCl and CuCl2 are stirred, and subsequently dried by evaporation. Finally, the mixture powders are dispersed into an orthogonal organic solvent solution of the salt by low-power and short-time ultrasonication, which exfoliates graphite into few-layer graphene sheets. We find that the as-made graphene sheets contain little oxygen, and 86% of them are 1-5 layers with lateral sizes as large as 210 μm(2). Importantly, the as-made graphene can be readily dispersed into aqueous solution in the presence of surfactant and thus is compatible with various solution-processing techniques towards graphene-based thin film devices.

Tip-Directed Synthesis of Multimetallic Nanoparticles.

Alloy nanoparticles are important in many fields, including catalysis, plasmonics, and electronics, due to the chemical and physical properties that arise from the interactions between their components. Typically, alloy nanoparticles are made by solution-based synthesis; however, scanning-probe-based methods offer the ability to make and position such structures on surfaces with nanometer-scale resolution. In particular, scanning probe block copolymer lithography (SPBCL), which combines elements of block copolymer lithography with scanning probe techniques, allows one to synthesize nanoparticles with control over particle diameter in the 2-50 nm range. Thus far, single-element structures have been studied in detail, but, in principle, one could make a wide variety of multicomponent systems by controlling the composition of the polymer ink, polymer feature size, and metal precursor concentrations. Indeed, it is possible to use this approach to synthesize alloy nanoparticles comprised of combinations of Au, Ag, Pd, Ni, Co, and Pt. Here, such structures have been made with diameters deliberately tailored in the 10-20 nm range and characterized by STEM and EDS for structural and elemental composition. The catalytic activity of one class of AuPd alloy nanoparticles made via this method was evaluated with respect to the reduction of 4-nitrophenol with NaBH4. In addition to being the first catalytic studies of particles made by SPBCL, these proof-of-concept experiments demonstrate the potential for SPBCL as a new method for studying the fundamental science and potential applications of alloy nanoparticles in areas such as heterogeneous catalysis.

3D-patterned polymer brush surfaces

Polymer brush-based three-dimensional (3D) structures are emerging as a powerful platform to engineer a surface by providing abundant spatially distributed chemical and physical properties. In this feature article, we aim to give a summary of the recent progress on the fabrication of 3D structures with polymer brushes, with a particular focus on the micro- and nanoscale. We start with a brief introduction on polymer brushes and the challenges to prepare their 3D structures. Then, we highlight the recent advances of the fabrication approaches on the basis of traditional polymerization time and grafting density strategies, and a recently developed feature density strategy. Finally, we provide some perspective outlooks on the future directions of engineering the 3D structures with polymer brushes.

Apertureless cantilever-free pen arrays for scanning photochemical printing.

A novel, apertureless, cantilever-free pen array can be used for dual scanning photochemical and molecular printing. Serial writing with light is enabled by combining self-focusing pyramidal pens with an opaque backing between pens. The elastomeric pens also afford force-tuned illumination and simultaneous delivery of materials and optical energy. These attributes make the technique a promising candidate for maskless high-resolution photopatterning and combinatorial chemistry.

Polymer Pen Lithography Using Dual‐Elastomer Tip Arrays

Dual-elastomer tip arrays are developed as a simple and cost-effective approach to significantly improve the uniformity and precision of polymer pen lithography (PPL). Both experiment and mechanical simulation demonstrate that the hard-apex, soft-base tip structure of the dual-elastomer tip array leads to precise control of feature size and reduced variation among different tips over large areas through fine control of the tip deformation. The dual-elastomer tip array is believed to be readily applied to fabricate nano- and microstructures for fundamental study and applications such as bioassays, sensors, optical and electronic devices.

High‐Resolution, Large‐Area, Serial Fabrication of 3D Polymer Brush Structures by Parallel Dip‐Pen Nanodisplacement Lithography

Parallel dip-pen nanodisplacement lithography (p-DNL) is used for high resolution, serial fabrication of 3D structures of polymer brushes over millimeter length scales. With p-DNL, 2D initiator templates consisting of arrays of nanolines and nanodots with rationally designed lateral spacings are fabricated in parallel via a locally tip-induced nanodisplacement process, from which highly defined 3D polymer structures are grown via surface-initiated atom transfer radical polymerization.

Polymer nanostructures made by scanning probe lithography: recent progress in material applications.

Scanning probe lithography (SPL) is a series of techniques that utilizes a scanning probe or an array of probes for surface patterning. Recent developments of new material systems and patterning approaches have made SPL a promising, low-cost, bench-top, and versatile tool for fabricating various polymer nanostructures, with extraordinary importance in physical sciences, life sciences and nanotechnology. This feature article highlights the recent progress in four material applications: polymer resists, polymeric carriers for patterning functional materials, electronically active polymers and polymer brushes for tailoring surface morphology and functionality. An overview of future possibilities, with regard to challenges and opportunities in this field, is given at the end of the paper.