Publications

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    ABSTRACT: Superhydrophobic surfaces are of immense scientific and technological interests for a broad range of applications. However, a major challenge remains in developing scalable methodologies that enable superhydrophobic coatings on versatile substrates with a combination of strong mechanical stability, optical transparency, and even stretchability. Herein, we developed a scalable methodology to versatile hydrophobic surfaces that combine with strong mechanical stability, optical transparency, and stretchability by using a self-assembled hydrogel as the template to in situ generate silica microstructures and subsequent silanization. The superhydrophobic coatings can be enabled on virtually any substrates via large-area deposition techniques like dip coating. Transparent surfaces with optical transmittance as high as 98% were obtained. Moreover, the coatings exhibit superior mechanical flexibility and robustness that it can sustain contact angles ∼160° even after 5000 cycles of mechanically stretching at 100% strain. The multifunctional surfaces can be used as screen filters and sponges for the oil/water separation that can selectively absorb oils up to 40× their weight.
    Nano letters. 06/2014;
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    ABSTRACT: Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1 Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.
    Nature Communications 01/2014; 5:3002. · 10.02 Impact Factor
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    ABSTRACT: Co3O4/graphene nanosheet (GNS) composites were synthesized via the in situ growth of mesoporous Co3O4 nanoparticles on graphene. The as-prepared Co3O4/GNS composites exhibited superior Li-ion battery performance and showed a large reversible capacity, excellent cycling, and good rate capability when used as an anode material in lithium ion batteries (LIBs). The uniform coating of Co3O4 around the graphene surface ensured tight electrical contact, resulting in a material with higher specific capacity and enhanced cycling performance compared with pure Co3O4 electrodes. The composites delivered a reversible capacity of 900 mA h g−1 at a discharge current density of 100 mA g−1 with good cycling ability. Moreover, the composites showed exceptional high-current charge–discharge performance, achieving 650 mA h g−1 at a current density of 1000 mA g−1.
    Materials Letters. 01/2014; 119:12–15.
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    ABSTRACT: Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).
    Nature Communications 06/2013; 4:1943. · 10.02 Impact Factor
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    ABSTRACT: Glucose enzyme biosensors have been shown useful for a range of applications from medical diagnosis, bioprocess monitoring, to beverage industry and environmental monitoring. We present here a highly sensitive glucose enzyme sensor based on Pt nanoparticles (PtNPs)-polyaniline (PAni) hydrogel heterostructures. High-density PtNPs were homogeneously loaded onto the three-dimensional (3D) nanostructured matrix of the PAni hydrogel. The PtNP/PAni hydrogel heterostructure-based glucose sensor synergizes the advantages of both the conducting hydrogel and the nanoparticle catalyst. The porous structure of the PAni hydrogel favored the high density immobilization of the enzyme and the penetration of water-soluble molecules, which helped efficiently catalyze the oxidation of glucose. In addition, the PtNPs catalyzed the decomposition of hydrogen peroxide that was generated during the enzymatic reaction. The transferred charges from these electrochemical processes were efficiently collected by the highly conducting PtNP/PAni hydrogel heterostructures. The glucose enzyme sensor based on this heterostructure exhibited unprecedented sensitivity, as high as 96.1 μA●mM-1●cm-2, with a response time as fast as 3 s, a linear range of 0.01 to 8 mM, and a low detection limit of 0.7 μM.
    ACS Nano 03/2013; · 12.06 Impact Factor
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    ABSTRACT: The exciting development of advanced nanostructured materials has driven the rapid growth of research in the field of electrochemical energy storage (EES) systems which are critical to a variety of applications ranging from portable consumer electronics, hybrid electric vehicles, to large industrial scale power and energy management. Owing to their capability to deliver high power performance and extremely long cycle life, electrochemical capacitors (ECs), one of the key EES systems, have attracted increasing attention in the recent years since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review article describes the most recent progress in the development of nanostructured electrode materials for EC technology, with a particular focus on hybrid nanostructured materials that combine carbon based materials with pseudocapacitive metal oxides or conducting polymers for achieving high-performance ECs. This review starts with an overview of EES technologies and the comparison between various EES systems, followed by a brief description of energy storage mechanisms for different types of EC materials. This review emphasizes the exciting development of both hybrid nanomaterials and novel support structures for effective electrochemical utilization and high mass loading of active electrode materials, both of which have brought the energy density of ECs closer to that of batteries while still maintaining their characteristic high power density. Last, future research directions and the remaining challenges toward the rational design and synthesis of hybrid nanostructured electrode materials for next-generation ECs are discussed.
    Nano Energy. 03/2013; 2(2):213–234.
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    ABSTRACT: A strategy of using structurally matched alumina insulation to produce lateral electrodes on semiconductor nanowires is presented. Nanowires in the architecture are structurally matched with alumina insulation using selective anodic oxidation. Lateral electrodes are fabricated by directly evaporating metallic atoms onto the opposite sides of the nanowires. The integrated architecture with lateral electrodes propels carriers to transport them across nanowires and is crucially beneficial to the injection/extraction in optoelectronics. The matched architecture and the insulating properties of the alumina layer are investigated experimentally. ZnO nanowires are functionalized into an ultraviolet photodiode as an example. The present strategy successfully implements an advantageous architecture and is significant in developing diverse semiconductor nanowires in optoelectronic applications.
    Nanotechnology 12/2012; 24(2):025204. · 3.84 Impact Factor
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    ABSTRACT: A continuous mesoporous iron oxide nanofilm was directly formed on graphene nanosheets through the in situ thermal decomposition of Fe(NO3)3·9H2O and was anchored tightly on the graphene surface. The lithiation-induced strain was naturally accommodated, owing to the constraint effect of graphene and the mesoporous structure. Hence, the pulverization of the iron oxide nanofilm was effectively prevented.
    RSC Advances 12/2012; 3(3):699-703. · 2.56 Impact Factor
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    ABSTRACT: Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (~480 F·g(-1)), unprecedented rate capability, and cycling stability (~83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (~0.3 s) and superior sensitivity (~16.7 μA · mM(-1)). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.
    Proceedings of the National Academy of Sciences 05/2012; 109(24):9287-92. · 9.74 Impact Factor
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    ABSTRACT: Two-dimensional transition-metal dichalcogenides such as MoS2 are promising channel materials for transistor scaling. Here, we report the performance and environmental effects on back-gated bi-layer MoS2 field-effect transistors. The devices exhibit Ohmic contacts with titanium at room temperature, on/off ratio higher than 107, and current saturation. Furthermore, we show that the devices are sensitive to oxygen and water in the ambient. Exposure to ambient dramatically reduces the on-state current by up to 2 orders of magnitude likely due to additional scattering centers from chemisorption on the defect sites of MoS2. We demonstrate that vacuum annealing can effectively remove the absorbates and reversibly recover the device performances. This method significantly reduces the large variations in MoS2 device caused by extrinsic factors.
    Applied Physics Letters 03/2012; 100(12). · 3.79 Impact Factor
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    ABSTRACT: Metal-diffusion-induced indium tin oxide (ITO) nanoparticles have been observed at the 2-amino-4,5-dicyanoimidazole (AIDCN)/ITO interface. X-ray photoelectron spectroscopy depth profiles reveal that the indium (In) and tin (Sn) elements of the nanoparticles are diffused from the ITO film into the organic layer. And the bonding states of In and Sn in the nanoparticles are identified to be In2O3 and SnO2, respectively. Furthermore, it is found that the ITO nanoparticles have an influence on the electrical property, causing electrical switching behaviour in the Al/AIDCN/ITO sandwich structure.
    Journal of Physics D Applied Physics 01/2012; 45:165104. · 2.53 Impact Factor
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    ABSTRACT: The electronic properties of graphene supported by the (0001) SiO2 surface are theoretically studied using density functional theory. It is found that the electronic attributes of graphene on (0001) SiO2 strongly depend on the underlying SiO2 surface properties and the percentage of hydrogen passivation. By applying methyl to passivate the oxygen-terminated (0001) SiO2 surface, one can further reduce the interaction between the graphene sheet and oxygen-terminated surface. This can improve the charge carrier mobility of graphene supported by SiO2 substrate and reduce the influence of residues of interfacial molecules. In addition, the external electric field modulates the charge transfer between graphene and the SiO2 surface when graphene layers are physisorbed on the oxide surface. This phenomenon will enhance the built-in electric field of bilayer graphene so as to effectively modify its band structure. Our results shed light on a better atomistic understanding of the recent experiments on graphene supported by SiO2.
    Journal of Physical Chemistry C. 01/2012; 116(10):6259-6267.
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    Y Li, C Liu, L Pan, L Pu
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    ABSTRACT: Charge trapping at organic/self-assembly molecule (SAM) interfaces is studied by the electrical switching behaviour in a crosspoint structure, where interfacial charge trapping tunes the potential barrier of the SAM layer. The sample with rubrene exhibits the write-once read-many-times memory effect, which is due to the interfacial charges trapped at deep states. On the other hand, the sample with 2-amino-4,5-dicyanoimidazole presents recyclable conduction transition, which results from the trapped charges distributed at shallow states. Moreover, the percentage of the charges trapped at shallow states can be estimated from electrical transition levels.
    Journal of Physics D Applied Physics 01/2012; 45:025104. · 2.53 Impact Factor
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    ABSTRACT: Graphene is an excellent substrate to load nanomaterials for energy applications due to its large surface area, excellent conductivity, mechanical strength, and chemical stability. In this study, thermal exfoliated functionalized graphene sheets with good conductivity and high BET surface area are anchored with mesoporous NiO nanoplates by in situ chemical synthesis approach. Electrochemical characterization shows that functionalized graphene sheets–NiO sample exhibits a high capacity of about 700mAh/g at a discharge current density of 100mA/g and a good cycling ability. The high capacity and good cycling ability of functionalized graphene sheets –NiO material were attributed to the intimate interaction between the graphene sheets and NiO nanoplates. The graphene sheets not only enhance the conductivity of NiO nanoplates but also improve the structure stability of NiO nanoplates. Furthermore, the mesoporous structure of NiO nanoplates is available to the transfer of electrolyte. Such functionalized graphene sheets–NiO nanocomposite could be a promising candidate material for a high-capacity, low cost, and nontoxic anode for lithium-ion batteries. KeywordsNiO nanoplates–Graphene–Mesoporous–Lithium-ion batteries
    Journal of Solid State Electrochemistry 01/2012; 16(5):1889-1892. · 2.28 Impact Factor
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    ABSTRACT: Bi2Te3 crystals with plate-like morphology have been successfully synthesized via a microwave-assisted heating approach in room temperature ionic liquid (RTIL) of 1-butyl-3-methylimidazolium bromide (C8H15BrN2). Scanning electronic microscopy (SEM) observation of as-synthesized Bi2Te3 confirmed their morphology of the hexagonal plates. It was observed that the edge and thickness values of as-synthesized Bi2Te3 were in the size of 0.5–2 μm and less than 100 nm, respectively. High-resolution transmission electronic microscopy (HR-TEM) and selected area electron diffraction (SAED) results revealed that the Bi2Te3 plates are of single-crystal in nature with the growth direction of 〈1 1 2¯ 0〉. In addition, as increasing the amount of ionic liquid, SEM results showed a novel evolution process of Bi2Te3 morphologies from mixture of Bi2Te3 nanorods and nanoplates to regular hexagonal plates, and then nanoplates with many small flecks. Furthermore, a possible mechanism regarding the formation of Bi2Te3 plates was proposed as well on the basis of the experimental results. The power factor of Bi2Te3 nanoplates is examined to evaluate its thermoelectric property.
    Journal of Alloys and Compounds. 05/2011; 509(20):6015–6020.
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    ABSTRACT: Ferroelectricity is attractive in data storage application as the polarizations can be used as binary levels. However, conductivity and ferroelectricity cannot be tuned independently in inorganic materials, thus two-terminal resistive memories with ferroelectrics are yet to be achieved. Here, we present an all-polymer-based system of semiconductor/ferroelectrics/semiconductor. Electrical switching behavior, which is critical to resistive memories, is observed. The mechanism of the conduction transition is attributed to the transmission probability of charge carriers tuned by electrical polarization. The importance of polarization in controlling the charge transport deserves further investigation for the realization and optimization of the two-terminal resistive memories with ferroelectrics.
    Applied Physics Letters 04/2011; 98(17):173306-173306-3. · 3.79 Impact Factor
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    ABSTRACT: Shuttle-shaped single-crystalline Te nanotubes decorated with spherical particles on outer surface have been successfully synthesized in reaction media of polyol solvent through a simple and rapid microwave-assisted approach. The length, outer diameter and wall thickness of as-synthesized Te nanotubes were roughly measured at 5-15 μm, 300-500 nm and 100-150 nm, respectively. The crystal growth process of Te nanotubes was investigated and discussed as the key issue of this present study, and it was found that the scrollinggrowth- based mechanism would best account for the formation process of the shuttle-shaped Te nanotubes. Photoluminance (PL) measurements displayed that the as-synthesized Te nanotubes can not only give strong violet blue emission but also strong red emission, and such unique optical property could be beneficial for nano-optical applications.
    Current Nanoscience 03/2011; 7(2):254-259. · 1.36 Impact Factor
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    ABSTRACT: ZnS nanodots highly dispersed on the surfaces of graphene sheets were successfully synthesized via an easy hydrothermal method by using Na2S as reducing agent as well as sulfide source. The reduction of graphite oxide (GO) to graphene was accompanied by the deposition of ZnS particles on the surface of graphene sheets. The results of X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) demonstrate the efficient reduction of GO to graphene sheets. The morphology characterization of the sample shows a wrinkled paper-like structure of the graphene sheets decorated with ZnS nanoparticles. Moreover, photoluminescence (PL) measurement shows a smooth spectrum, indicating fewer defects in the composite.
    Materials Letters - MATER LETT. 01/2011; 65(2):198-200.
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    ABSTRACT: A high ZT value is predicted in laterally-coupled nanowire arrays. The quantum confinement and coupling of electrons are considered in the framework of effective-mass envelope-function theory. The boundary scattering on phonons is also taken into account. The thermoelectric properties benefit from the large Seebeck coefficient and dramatically reduced lattice thermal conductivity, as well as the preserved electronic conductivity in the minibands of the coupling nanowires. The enhancement of ZT to more than 10-fold is achieved in the n-type Si nanowires/Ge host material. Results suggest that the laterally-coupled nanowire arrays can be designed for high-performance thermoelectric devices.
    Physics Letters A 01/2011; 375(28):2728-2732. · 1.77 Impact Factor

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