Zheng Yan

University of Illinois, Urbana-Champaign | UIUC · Department of Materials Science and Engineering

Piezoelectric microsystems are of use in areas such as mechanical sensing, energy conversion and robotics. The systems typically have a planar structure, but transforming them into complex three-dimensional (3D) frameworks could enhance and extend their various modes of operation. Here, we report a controlled, nonlinear buckling process to convert...

Efficient and highly functional three-dimensional systems that are ubiquitous in biology suggest that similar design architectures could be useful in electronic and optoelectronic technologies, extending their levels of functionality beyond those achievable with traditional, planar two-dimensional platforms. Complex three-dimensional structures ins...

Recently developed methods for mechanically-guided assembly exploit stress release in prestretched elastomeric substrates to guide the controlled formation of complex three-dimensional (3D) mesostructures in advanced functional materials and integrated electronic devices. The techniques of interfacial photopolymerization allow for realization of su...

The development of methods to synthesize and physically manipulate extremely thin, single-crystalline inorganic semiconductor materials—so-called nanomembranes—has led to an almost explosive growth of research world-wide into uniquely enabled opportunities for their use in new ‘soft’ and other unconventional form factors for high-performance electr...

Three-dimensional (3D) structures capable of reversible transformations in their geometrical layouts have important applications across a broad range of areas. Most morphable 3D systems rely on concepts inspired by origami/kirigami or techniques of 3D printing with responsive materials. The development of schemes that can simultaneously apply acros...

In article number 1703852, Andreas A. Polycarpou and co-workers fabricate and study the deformation of three-dimensional (3D) multilayered Kirigami microstructures with potential applications in 3D microelectromechanical systems (MEMS) devices. The mechanical response under flat-punch compression is studied using combined experiments and finite ele...

Mechanically guided 3D microassembly with controlled compressive buckling represents a promising emerging route to 3D mesostructures in a broad range of advanced materials, including single-crystalline silicon (Si), of direct relevance to microelectronic devices. During practical applications, the assembled 3D mesostructures and microdevices usuall...

Recent progress in the synthesis and deterministic assembly of advanced classes of single crystalline inorganic semiconductor nanomaterial establishes a foundation for high-performance electronics on bendable, and even elastomeric, substrates. The results allow for classes of systems with capabilities that cannot be reproduced using conventional wa...

Significance Exploiting advanced 3D designs in micro/nanomanufacturing inspires potential applications in various fields including biomedical engineering, metamaterials, electronics, electromechanical components, and many others. The results presented here provide enabling concepts in an area of broad, current interest to the materials community––s...

In article number 1700068, John A. Rogers, Ralph G. Nuzzo, and co-workers present direct ink write (DIW)-assisted integration of soft and cellular materials onto compressively buckled microframeworks that are constructed using polymer or high performance silicon semiconductor membranes. These scaffolds provide unique 3D environments upon which to s...

Complex 3D organizations of materials represent ubiquitous structural motifs found in the most sophisticated forms of matter, the most notable of which are in life-sustaining hierarchical structures found in biology, but where simpler examples also exist as dense multilayered constructs in high-performance electronics. Each class of system evinces...

Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches for origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies, and/or capability for reversible co...

Formation of 3D mesostructures in advanced functional materials is of growing interest due to the widespread envisioned applications of devices that exploit 3D architectures. Mechanically guided assembly based on compressive buckling of 2D precursors represents a promising method, with applicability to a diverse set of geometries and materials, inc...

Nature Reviews Materials 2 , 17019 (2017) In the originally published version of this article, there was an error in the Acknowledgements section. This has been corrected in both the HTML and PDF versions.

Microelectromechanical systems remain an area of significant interest in fundamental and applied research due to their wide ranging applications. Most device designs, however, are largely 2D and constrained to only a few simple geometries. Achieving tunable resonant frequencies or broad operational bandwidths requires complex components and/or fabr...

A rapidly expanding area of research in materials science involves the development of routes to complex 3D structures with feature sizes in the mesoscopic range (that is, between tens of nanometres and hundreds of micrometres). A goal is to establish methods for controlling the properties of materials systems and the function of devices constructed...

Approaches capable of creating 3D mesostructures in advanced materials (device-grade semiconductors, electroactive polymers, etc.) are of increasing interest in modern materials research. A versatile set of approaches exploits transformation of planar precursors into 3D architectures through the action of compressive forces associated with release...

This chapter focuses on semiconductor nanomembranes (NMs) in general, and silicon NMs in particular, as a class of electronic material for devices that can bend, fold, and stretch without significant change in properties. The content begins with procedures for creating such materials, and for manipulating them using the techniques of transfer print...

D helical mesostructures are attractive for applications in a broad range of microsystem technologies due to their mechanical and electromagnetic properties as stretchable interconnects, radio frequency antennas, and others. Controlled compressive buckling of 2D serpentine-shaped ribbons provides a strategy to formation of such structures in wide r...

Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches for origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies, and/or capability for reversible co...

Significance Existing options in three-dimensional (3D) assembly of micro/nanomaterials are constrained by a narrow accessible range of materials and/or 3D geometries. Here we introduce concepts for a form of Kirigami for the precise, mechanically driven assembly of 3D mesostructures from 2D micro/nanomembranes with strategically designed geometrie...

Here we investigated the fluorination of graphene oxide nanoribbons (GONR) using H2 and F2 gasses at low temperature, below 200°C, with the purpose of elucidating their structure and predicting a fluorination mechanism. The importance of this study is the understanding of how fluorine functional groups are incorporated to complex structures, such a...

Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal str...

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...

The synthesis of rebar graphene on Cu substrates is described using functionalized boron nitride nanotubes (BNNTs) that were annealed or subjected to chemical vapor deposition (CVD) growth of graphene. Characterization shows that the BNNTs partially unzip and form a reinforcing bar (rebar) network within the graphene layer that enhances the mechani...

Metal grids covered by graphene were used as transparent conductive electrodes in dye sensitized solar cells. The efficiency of dye sensitized solar cells with graphene-on-Pt grids was 0.4%. Compared to the control group, in which the platinum grids were used as a transparent conductive layer, the efficiency of dye sensitized solar cells with graph...

The thermal conduction of suspended few-layer hexagonal boron nitride (h-BN) sheets was experimentally investigated using a noncontact micro-Raman spectroscopy method. The first-order temperature coefficients for monolayer (1L), bilayer (2L) and nine-layer (9L) h-BN sheets were measured to be -(3.41 +/- 0.12) x 10(-2), -(3.15 +/- 0.14) x 10(-2) and...

As the cylindrical sp(2)-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, like graphene, are still absent. Here we demonstra...

A composite material made of graphene nanoribbons and iron oxide nanoparticles provides a remarkable route to lithium-ion battery anode with high specific capacity and cycle stability. At a rate of 100 mA/g, the material exhibits a high discharge capacity of ~910 mAh/g after 134 cycles, which is >90% of the theoretical li-ion storage capacity of ir...

As a two-dimensional (2D) sp2-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and l...

Bi- and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high-quality large-size bi- and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid-like hexagonal bi- and trilayer gra...

A thermoplastic polyurethane (TPU) composite film containing hexadecyl-functionalized low-defect graphene nanoribbons (HD-GNRs) was produced by solution casting. The HD-GNRs were well distributed within the polyurethane matrix, leading to phase separation of the TPU. Nitrogen gas effective diffusivity of TPU was decreased by three orders of magnitu...

Patterning ultrathin MoS2 layers with regular edges or controllable shapes is appealing since the properties of MoS2 sheets are sensitive to the edge structures. In this work, we have introduced a simple, effective and well-controlled technique to etch layered MoS2 sheets with well-oriented equilateral triangular pits by simply heating the samples...

Two types of graphene oxide fibers are spun from high concentration aqueous dopes. Fibers extruded from large flake graphene oxide dope without drawing show unconventional 100% knot efficiency. Fibers spun from small sized graphene oxide dope with stable and continuous drawing yield in good intrinsic alignment with a record high tensile modulus of...

Precise spatial control of materials is the key capability of engineering their optical, electronic and mechanical properties. However, growth of graphene on Cu was revealed to be seed-induced 2D growth, limiting the synthesis of complex graphene spatial structures. In this research, we report the growth of onion ring-like 3D graphene structures, w...

A composite made from graphene nanoribbons (GNRs) and tin oxide (SnO2) nanoparticles (NPs) is synthesized and used as the anode material for lithium ion batteries (LIBs). The conductive GNRs, prepared using sodium/potassium unzipping of multiwall carbon nanotubes, can boost the lithium storage performance of SnO2 NPs. The composite, as an anode mat...

The electrical properties of chemically derived graphene and graphene grown by chemical vapor deposition (CVD), until now, have been inferior to those of mechanically exfoliated graphene. However, because graphene is easier to produce in large quantities through CVD or growth from solid carbon sources, it has a higher potential for use in future el...

In this research, 3-dimensional (3D) graphene carbon nanotube carpets (G/CNTCs)-based microsupercapacitors (G/CNTCs-MCs) were fabricated in situ on nickel electrodes. The G/CNTCs-MCs show impedance phase angle of -81.5° at a frequency of 120 Hz, comparable to commercial aluminum electrolytic capacitors (AECs) for alternating current (ac) line filte...

Graphene was grown directly on porous nickel films, followed by the growth of controlled lengths of vertical carbon nanotube (CNT) forests that seamlessly emanate from the graphene surface. The metal-graphene-CNT structure is used to directly fabricate field-emitter devices and double-layer capacitors. The three dimensional nanostructured hybrid ma...

Graphene and single-walled carbon nanotubes are carbon materials that exhibit excellent electrical conductivities and large specific surface areas. Theoretical work suggested that a covalently bonded graphene/single-walled carbon nanotube hybrid material would extend those properties to three dimensions, and be useful in energy storage and nanoelec...

Few-layer graphene, with Bernal stacking order, is of particular interests to the graphene community because of its unique tunable electronic structure. A synthetic method to produce such large area graphene films with precise thickness from 2 to 4 layers would be ideal for chemists and physicists to explore the promising electronic applications of...

Transparent electronic memory would be useful in integrated transparent electronics. However, achieving such transparency produces limits in material composition, and hence, hinders processing and device performance. Here we present a route to fabricate highly transparent memory using SiO(x) as the active material and indium tin oxide or graphene a...

In this research, we constructed a controlled chamber pressure CVD (CP-CVD) system to manipulate graphene's domain sizes and shapes. Using this system, we synthesized large (∼4.5 mm(2)) single-crystal hexagonal monolayer graphene domains on commercial polycrystalline Cu foils (99.8% purity), indicating its potential feasibility on a large scale at...

We have fabricated a centimeter-size single-layer graphene device with a gate electrode, which can modulate the transmission of terahertz and infrared waves. Using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy in a wide frequency range (10-10 000 cm(-1)), we measured the dynamic conductivity change induced by electr...

A controlled ambipolar-to-unipolar (n-type) conversion, along with a maximum fourfold increase in the electron mobility, in graphene field-effect transistors (FETs) is achieved by coating the surface of graphene with a layer of a mixed polymer system, poly(ethylene imine) (PEI) in poly(ethylene glycol) (PEG). The PEG serves as a physisorption adhes...

The controllable and reversible modification of graphene by chemical functionalization can modulate its optical and electronic properties. Here we demonstrate the controlled patterning of graphane/graphene superlattices within a single sheet of graphene. By exchanging the sp(3) C-H bonds in graphane with sp(3) C-C bonds through functionalization, s...

Conductive carbon material-coated Kevlar fibers were fabricated through layer-by-layer spray coating. Polyurethane was used as the interlayer between the Kevlar fiber and carbon materials to bind the carbon materials to the Kevlar fiber. Strongly adhering single-walled carbon nanotube coatings yielded a durable conductivity of 65 S/cm without signi...

Here we demonstrate a general transfer-free method to directly grow large areas of uniform bilayer graphene on insulating substrates (SiO(2), h-BN, Si(3)N(4), and Al(2)O(3)) from solid carbon sources such as films of poly(2-phenylpropyl)methysiloxane, poly(methyl methacrylate), polystyrene, and poly(acrylonitrile-co-butadiene-co-styrene), the latte...

Here we report a transfer-free method of synthesizing bilayer graphene directly on SiO(2) substrates by carbon diffusion through a layer of nickel. The 400 nm nickel layer was deposited on the top of SiO(2) substrates and used as the catalyst. Spin-coated polymer films such as poly(methyl methacrylate), high-impact polystyrene or acrylonitrile-buta...

Transparent, flexible conducting films were fabricated by using a metallic grid and graphene hybrid film. Transparent electrodes using the hybrid film and transparent substrate such as glass or polyethylene terephthalate (PET) films were assembled. The sheet resistance of the fabricated transparent electrodes was as low as 3 Ω/◻ with the transmitta...

Graphene is predicted to offer new opportunities for terahertz (THz) science and technology. Its zero-gap linear band dispersion is expected to lead to exotic nonlinear electromagnetic properties, which can be probed through frequency-dependent conductivity measurements. Here, we use THz time-domain spectroscopy and Fourier-transform infrared spect...

In this study, with self-assembled monolayers (SAMs) of aminopropyl-, ammoniumpropyl-, butyl-, and 1H,1H,2H,2H-perfluorooctyltriethoxysilanes deposited in-between graphene and the SiO(2) substrate, a controlled doping of graphene was realized with a threshold voltage ranging from -18 to 30 V. In addition, the SAMs are covalently bonded to the SiO(2...

Monolayer graphene was first obtained as a transferable material in 2004 and has stimulated intense activity among physicists, chemists and material scientists. Much research has been focused on developing routes for obtaining large sheets of monolayer or bilayer graphene. This has been recently achieved by chemical vapour deposition (CVD) of CH(4)...

A novel silane bearing a reactive anhydride group was synthesized. Due to its special structure, the direct co-condensation of this synthesized functional silane with TEOS in the presence of different surfactant templates led to ordered mesoporous silicas with different pore sizes and a high density of carboxylic acid groups, which were used as ads...

Pyridine-functionalized mesoporous silica was prepared via direct condensation of tetraethoxysilane (TEOS) and N-(3-(triethoxysilyl)propyl)isonicotinamide using the copolymer P123 as structure-directing agent, and employed as adsorbent for the removal of alizarin red S, reactive brilliant red X-3B and reactive yellow X-RG from waste water. The adso...

Amphiphilic chitooligosaccharide-graft-poly(epsilon-caprolactone) (COS-g-PCL) copolymers were controllably synthesized using protection/deprotection technique of COS via trimethylsilyl groups and ring-opening polymerization of F-caprolactone. Their crystalline properties were investigated with differential scanning calorimetry. With the increase of...