Qingyu Yan

Abstract: Successful attempts have been made to control the synthesis of tubular MnOOH with nanodimensions on high electronic conductivity graphite felt (GF) to be used as a flexible supercapacitor electrode. As a fundamental study, the time-dependent kinetics was investigated to interpret its formation mechanism, which can be depicted as the curling of a two-dimensional precursor into a one-dimensional structure with a hollow interior. As a result of the nanotube structure, the active surface area of MnOOH is completely accessible to electrolyte ions and has a shorter charge-transport length and greater ability to withstand structural deformation. Hence, hollow-structured MnOOH shows great promise as an electrochemical system, which is reflected in its high specific capacitance of 1156Fg-1 at 1Ag-1. Furthermore, the high energy density of 1125Whkg-1 and power density of 5.05kWkg-1 reveal the outstanding energy-storage behavior of the MnOOH/GF composites as flexible supercapacitor electrodes.

Abstract: Enhancing ion and electron transport kinetics together with improving cycle life are important issues to be considered when developing high-performance Li ion batteries. Here we demonstrate a three dimensional ordered macroporous conductive electrode concept by entrapping electrode active nanoparticles in an interpenetrating macroporous carbon inverse opal. The electrodes are featured with simultaneously enhanced ion and electron transport kinetics as well as geometrically constrained active nanoparticles. The electrode can deliver up to 94.17% of theoretical capacity over 1000 discharge/charge cycles at a current density of 2.0 A g(-1), and exhibits good rate capability in the high current density range of 1.0-10.0 A g(-1). We hope that our findings will help pave the way for tailored design of many other sophisticated electrode materials in electrochemistry.

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Abstract: We report a simple approach to prepare the nitrogen-modified few-layer graphene (FLG) directly from graphite flakes. With the aid of melamine, graphite flakes can be directly ultrasonicated into FLG in acetone. The subsequent annealing process further transforms the melamine absorbed on the surface of graphene into melon (C6N9H3)(x), which is one type of condensation product of melamine, and simultaneously dopes the graphene with nitrogen. When tested as a supercapacitor electrode, the nitrogen-modified FLG shows a much higher specific capacitance (e.g., 227 F/g at 1A/g) than that of reduced graphene oxide (rGO) (e.g., 133 F/g at 1A/g). (C) 2013 Elsevier Ltd. All rights reserved.

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Abstract: Few-layer V2O5 nanosheets with a thickness of 2.1-3.8 nm have been successfully synthesized in this work via a simple and scalable liquid exfoliation technique. The unique nanostructure allows the high-rate transportation of lithium ions and electrons due to very short diffusion paths provided by this ultrathin thickness, resulting in Li-ion cathodes with remarkable energy and power densities.

Abstract: Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li+ to diffuse over a [010]-thickness of <5 nm (1) was calculated to be less than 25, 2.5, and 250 mu s for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L-2/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

Abstract: Hollow hierarchical spheres self-organized from the ultrathin nanosheets of alpha-Fe2O3 were prepared by a simple process. These ultrathin nanosheet subunits possess an average thickness of around 3.5 nm and show preferential exposure of (1 1 0) facets. Their Li ion storage and visible-light photocatalytic water oxidation performance are tested. Such hierarchical nanostructures show high Li storage properties with good cycling stability and excellent rate capabilities. The water oxidation catalytic activity is 70 mu mol h(-1) g(-1) for O-2 evolution under visible light irradiation and can be maintained for 15 hours. The structural features of these alpha-Fe2O3 nanocrystals are considered to be important to lead to the attractive properties in both Li storage and photocatalytic water oxidation, e. g. hollow interior, ultrathin thickness and largely exposed active facets.

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Abstract: Hierarchical urchin-like hollow spheres (5-8 mu m in diameter) assembled by one-dimensional nanowires consisting of many interconnected Co3O4 nanoparticles (10-50 nm) are successfully synthesized. Co(CO3)(0.5)(OH)center dot 0.11H(2)O precursors are firstly prepared by a hydrothermal process. The morphological evolution process of Co(CO3)(0.5)(OH)center dot 0.11H(2)O hollow urchin precursors is investigated and a plausible mechanism is proposed. Then, the Co(CO3)(0.5)(OH)center dot 0.11H(2)O are converted to Co3O4 through heat treatment in air. As an anode material for lithium ion batteries, urchin-like Co3O4 hollow spheres exhibit highly reversible specific capacities, good cycling stabilities and excellent rate capabilities (e.g., 433 mAh g(-1) at 10 C). The superior performances result from the synergetic effect of integral urchin-like microstructure, small diffusion lengths in the nanoparticle building blocks and sufficient void space to buffer the volume expansion. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: A facile thermal decomposing method has been developed for the fabrication of CoxP nanostructures with controlled size, phase, and shape (e.g., Co2P rod and spheres, CoP hollow and solid particles). An amorphous carbon layer could be introduced by the carbonization of organic surfactants from the precursors. The electrochemical performance of typical CoP and Co2P samples as anode materials has been investigated and the CoP hollow nanoparticle with carbon coating layer depicts good capacity retention and high rate capability (e.g., specific capacity of 630 mA h g(-1) at 0.2 C after 100 cycles, and a reversible capacity of 256 mA h g(-1) can be achieved at a high current rate of 5 C).

Abstract: A facile, environmentally friendly, and economical synthetic route for production of large-amounts (gram scale) of two-dimensional (2D) layered SnS2 nanoplates is presented. The electrode fabricated from the SnS2 nanoplate exhibits excellent lithium-ion battery performance with highly reversible capacity, good cycling stability and excellent capacity retention after 30 cycles.

Abstract: Hierarchical vanadium oxide nanoflowers (V10O24 center dot nH(2)O) were synthesized via a simple, high throughput method employing a fast electrochemical reaction of vanadium foil in NaCl aqueous solution, followed by an aging treatment at room temperature. During the electrochemical process, the anodic vanadium foil is dissolved in the form of multi-valence vanadium ions into the solution, driven by the applied electrical field. After being oxidized, the VO2+ and VO2+ ions instantly react with the OH+ in the electrolyte to form uniformly distributed vanadium oxide nanoparticles at a high solution temperature due to the exothermic nature of the reaction. Finally, nucleation and growth of one dimensional nanoribbons takes place on the surface of the nanoparticles during the aging process to form unique hierarchical V10O24 center dot nH(2)O nanoflowers. Upon heat treatment, the hierarchical architecture of the vanadium pentoxide nanoflower morphology is maintained. Such a material provides porous channels, which facilitate fast ion diffusion and effective strain relaxation upon Li ion charge-discharge cycling. The electrochemical tests reveal that the V2O5 nanoflowers cathode could deliver high reversible specific capacities with 100% coulombic efficiency, especially at high C rates (e.g., 140 mAh g(-1) at 10 C).

Abstract: A facile route for synthesizing size- and shape-controlled ternary hexagonal ZnIn2S4 nanocrystals with narrow size distributions is developed using oleylamine as the ligand and noncoordinating octadecene as the solvent. Tunable sizes from 2.1 nm to 9.2 nm of the ZnIn2S4 nanocrystals are achieved through manipulation of reaction temperatures. Furthermore, the obtained ZnIn2S4 presents a nanoplate structure by replacing the sulfur powder with thiourea as the sulfur source. Optical measurements of the ZnIn2S4 nanocrystals demonstrate that their optical properties are related to the sizes of the products. The band gap energy varies from 3.28 to 2.35 eV, corresponding to the size from 2.1 nm to 9.2 nm. Compared with the bulk material, the blue-shift of the absorption spectra is mainly due to the size- dependent quantum confined effect. Photodegradation investigation demonstrates that the annealed ZnIn2S4 nanocrystals reveal higher photocatalytic activity for degradation of methylene orange ( MO) solution in the visible region than the annealed ZnIn2S4 nanoplates and unannealed ZnIn2S4 nanocrystals.

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Abstract: A simple, non-template, non-surfactant and environmentally friendly hydrothermal method is presented based on the controlled release of the reactants into the reaction solvents to induce slow nucleation and growth of three-dimensional hierarchical nanostructures of transition metal oxides. This method is a general approach, which can be used to prepare Co3O4, CuO, and Ni(OH)(2)/NiO. These metal oxides with hierarchical nanostructures can be used as anode materials for lithium-ion batteries with good Li storage performance, e. g. high specific capacities and stable cyclability.

Abstract: We report a facile method to prepare nanoarchitectured metal oxides/graphene hybrids as both positive and negative electrodes for Li-ion batteries. The metal oxides/graphene hybrids were synthesized by deposition of metal oxides and exfoliation of graphene sheets in a one-step electrochemical process. The hybrid electrodes showed high specific capacities with excellent cycling stability. For example, the Fe2O3/graphene anode was able to deliver a discharge capacity of up to 894 mA h g(-1) during the 50th cycle at 0.3 C. Co3O4/graphene depicted a discharge capacity of 880 mA h g(-1) during the 40th cycle at 0.3 C. The V2O5/graphene cathode delivered a discharge capacity of 208 mA h g(-1) during the 100th cycle at 6.8 C.

Abstract: In this work, n-type Ag2Te nanoparticles are prepared by a solvothermal approach with uniform and controllable sizes, e. g. 5-15 nm. The usage of dodecanethiol during the synthesis effectively introduces sulfur doping into the sample, which optimizes the charge carrier concentration of the nanoparticles to >1 x 10(20) cm(-3). This allows us to achieve the desired electrical resistivities of <5 x 10(-6) Omega m. It is demonstrated that Ag2Te particles prepared by this solvothermal process can exhibit high ZT values, e. g. 15 nm Ag2Te nanoparticles with effective sulphur doping show a maximum ZT value of similar to 0.62 at 550 K.

Abstract: Fe2O3 nanocluster-decorated graphene (Fe2O3/graphene) hybrids with controlled contents of Fe2O3 were prepared by a facile electrochemical process. These Fe2O3/graphene hybrids were tested as O-2 electrodes for Li-O-2 batteries, which exhibited enhanced discharge capacities as compared to that of a pure graphene based O-2 electrode, e.g. the Fe2O3/graphene electrode with 29.0 wt% of Fe2O3 delivered a discharge capacity of 8290 mA h g(-1) and a round-trip efficiency of 65.9% as compared to 5100 mA h g(-1) and 57.5% for a pure graphene electrode. The excellent electrochemical properties of Fe2O3/graphene as an O-2 electrode is ascribed to the combination of the fast kinetics of electron transport provided by the graphene sheets and the high electrocatalytic activity for O-2 reduction provided by the Fe2O3.

Abstract: Amorphous FeVO4 nanosheet arrays have been grown directly from a flexible stainless steel (SS) substrate by a facile template-free and catalyst-free chemical vapour deposition (CVD) method. These FeVO4 nanosheets showed superior Li storage properties, especially at high current densities.

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Abstract: Novel cationic quaternary chalcohalide nanobelts were found in Hg(4)In(2)Q(3)Cl(8) (Q = S, Se, Te), obtained by solid-state reaction. Due to the effects of dimensional reduction, both theoretical and experimental results demonstrate that their bandgaps are remarkably increased compared to those of the zinc-blende structure HgQ (Q = S, Se, Te).

Abstract: We show that seeded growth can be applied to creating two-dimensional (2D) dendritic Au nanostructures on sample grids, which can be directly characterized by transmission electron microscopy (TEM). The 2D synthesis of highly consistent structures offers a novel mechanistic perspective on the aggregation of colloidal Au nanocrystals on a surface.

Abstract: A large-area, continuous, few-layer reduced graphene oxide (rGO) thin film has been fabricated on a Si/SiO(2) wafer using the Langmuir-Blodgett (LB) method followed by thermal reduction. After photochemical reduction of Pt nanoparticles (PtNPs) on rGO, the obtained PtNPs/rGO composite is employed as the conductive channel in a solution-gated field effect transistor (FET), which is then used for real-time detection of hybridization of single-stranded DNA (ssDNA) with high sensitivity (2.4 nM). Such a simple, but effective method for fabrication of rGO-based transistors shows great potential for mass-production of graphene-based electronic biosensors.

Abstract: Ag-doped Ca3Co4O9 thin films with nominal composition of Ca3-xAgxCo4O9 (x = 0 similar to 0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x <= 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca3Co4O9 thin films could reach 0.73 mW m(-1) K-2 at around 700 K, which was about 16% higher than that of the pure Ca3Co4O9 thin film. (C) 2011 Elsevier B. V. All rights reserved.

Abstract: Uniform carbon-coated single crystalline vanadium dioxide (VO2(B)@C) nanobelts were successfully prepared by using a facile one-pot hydrothermal approach. Sucrose plays a dual role in this hydrothermal process, namely as a carbon precursor for the carbon shell and, as a reductant to reduce V2O5 to VO2(B). The thickness of the carbon coating layer is tunable from 3.0 to 6.9 nm by changing the ratio of the precursors. Although a high carbon content can improve the electrical conductivity of VO2(B)@C nanobelts, a thick carbon coating layer would block the lithium ion diffusion. The optimal thickness is found to be 4.3 nm (carbon content: 6.6 wt%), where the cathode displays superior performance with highly reversible specific capacities, good cycling stabilities and excellent rate capabilities (e.g. 100 mA h g(-1) at 12.4 C).

Abstract: Although theoretical calculations indicate that the thermoelectric figure of merit, ZT, of carbon nanotubes (CNTs) could reach >2, the experimentally reported ZT values of CNTs are typically in the range of 10(-3)-10(-2), which is not attractive for thermal energy conversion applications. In this work, we report the preparation of flexible CNT bulky paper for thermoelectric applications. The ZT values of the CNT bulky papers could be significantly enhanced by Ar plasma treatment, i.e. increasing it from 0.01 for pristine CNTs to 0.4 for Ar-plasma treated CNTs. The improved thermoelectric properties were mainly due to the greatly increased Seebeck coefficients and a reduction in the thermal conductivities, although the electrical conductivities also decreased. Such an improvement makes the plasma treated CNT bulky papers promising as a new type of thermoelectric material for certain niche applications as they are easily processed, mechanically flexible and durable, and chemically stable.

Abstract: Microcrystalline alpha-iron oxyhydroxide/reduced graphene oxide (alpha-FeOOH/rGO) samples have been successfully synthesized by a facile hydrothermal process. The alpha-FeOOH/rGO samples are either hexagonal disks with a diameter of similar to 1 mu m and a thickness of 300 nm or hexapods with a diameter of similar to 2 mmand a thickness of 700 nm, while only bulk and aggregated FeOOH is observed without the addition of graphene oxide sheets. The size and shape of the alpha-FeOOH depend on the reaction time, concentration of Fe3+, and the addition of graphene oxide. The growth of the hexagonal disks and hexapods is mainly due to a series of phase and structural transformations. The alpha-FeOOH/rGO displays superior anode performance with a high reversible specific capacity of 569 mA h g(-1) at the 50(th) cycle.

Abstract: Employing in situ-formed new organic ligands, two Pb(II)-based metal-organic frameworks were synthesized. Compound 1 possesses a 3D framework while compound 2 has a layered structure. Solid state UV-visible absorptions indicate that the two compounds are semiconductors with band gaps of 1.70 and 1.78 eV. Magnetic properties reveal that they are temperature-independent diamagnetic.

Abstract: The comparison between two kinds of single-layer reduced graphene oxide (rGO) sheets, obtained by reduction of graphene oxide (GO) with the electrochemical method and hydrazine vapor reduction, referred to as E-rGO and C-rGO, respectively, is systematically studied. Although there is no morphology difference between the E-rGO and C-rGO films adsorbed on solid substrates observed by AFM, the reduction process to obtain the E-rGO and C-rGO films is quite different. In the hydrazine vapor reduction, the nitrogen element is incorporated into the obtained C-rGO film, while no additional element is introduced to the E-rGO film during the electrochemical reduction. Moreover, Raman spectra show that the electrochemical method is more effective than the hydrazine vapor reduction method to reduce the GO films. In addition, E-rGO shows better electrocatalysis towards dopamine than does C-rGO. This study is helpful for researchers to understand these two different reduction methods and choose a suitable one to reduce GO based on their experimental requirements.

Abstract: Li3V2(PO4)(3) nanocrystals (5-8 nm) embedded in a nanoporous carbon matrix attached onto reduced graphene oxide nanosheets (LVP-NC@NPCM@rGO) are synthesized by a facile approach. The rGO sheets not only form the interconnected conducting scaffold to enhance the charge transfer but also act as the heterogeneous nucleation site to facilitate the growth of nanograins of LVR The nanoporous carbon acts as the nanocontainer to enhance the electrolyte/active material interaction and also inhibit the grain growth of Li3V2(PO4)(3). This leads to the fast kinetics of the Li ion transfer and the excellent cathode performance, especially at high current densities. Binder-free cathodes can be prepared based such LVP-NC@NPCM@rGO sample, which shows high specific capacities, stable cyclabilities and excellent rate capabilities in the voltage ranges of 3.0-4.3 and 3.0-4.8 V. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Carbon monoxide (CO) is a highly toxic gas that can be commonly found in many places. However, it is not easily detected by human olfaction due to its colorless and odorless nature. Therefore, highly sensitive sensors need to be developed for this purpose. Carbon nanotubes (CNTs) have an immense potential in gas sensing. However, CNT-based gas sensors for sensing CO are seldom reported due to the lack of reactivity between CO and CNTs. In this work, O-2 plasma modified CNT was used to fabricate a CNT gas sensor. The plasma treated CNTs showed selectively towards CO, with the capability of sensing low concentrations of CO (5 ppm) at room temperature, while the pristine CNTs showed no response. UV spectra and oxygen reduction reaction provided evidence that the difference in sensing property was due to the elimination of metallic CNTs and enhancement of the oxygen reduction property.

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Abstract: We report a facile method to prepare a nanoarchitectured lithium manganate/graphene (LMO/G) hybrid as a positive electrode for Li-ion batteries. The Mn2O3/graphene hybrid is synthesized by exfoliation of graphene sheets and deposition of Mn2O3 in a one-step electrochemical process, which is followed by lithiation in a molten salt reaction. There are several advantages of using the LMO/G as cathodes in Li-ion batteries: (1) the LMO/G electrode shows high specific capacities at high gravimetric current densities with excellent cycling stability, e. g., 84 mAh.g(-1) during the 500th cycle at a discharge current density of 5625 mA.g(-1) (similar to 38.01 C capacity rating) in the voltage window of 3-4.5 V; (2) the LMO/G hybrid can buffer the Jahn-Teller effect, which depicts excellent Li storage properties at high current densities within a wider voltage window of 2-4.5 V, e. g., 93 mAh.g(-1) during the 300th cycle at a discharge current density of 5625 mA.g(-1) (similar to 38.01 C). The wider operation voltage window can lead to increased theoretical capacity, e. g., 148 mAh.g(-1) between 3 and 4.5 V and 296 mAh.g(-1) between 2 and 4.5 V; (3) more importantly, it is found that the attachment of LMO onto graphene can help to reduce the dissolution of Mn2+ into the electrolyte, as indicated by the inductively coupled plasma (ICP) measurements, and which is mainly attributed to the large specific surface area of the graphene sheets.

Abstract: Si nanowires in graphene papers were successfully prepared by supercritical fluid-liquid-solid (SFLS) process, which showed high specific capacities and charge-discharge cycling stability as anode materials for Li-ion storage. The enhancement on capacity and cycling stability of the Si/graphene composite nanostructures was attributed to the presence of graphene papers in the hybrid samples that served as a highly conductive framework and absorption of volume changes of Si nanowires during the lithiation/delithiation process. This Si/graphene electrodes maintained reversible capacities of 1400 mAh g(-1) for the 30th cycle at a current density of 420 mA g(-1), which is much better as compared to that of pure Si nanowires. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: Although many oxide semiconductors possess wide bandgaps in the ultraviolet (UV) regime, currently the majority of them cannot efficiently emit UV light because the band-edge optical transition is forbidden in a perfect lattice as a result of the symmetry of the band-edge states. This quantum mechanical rule severely constrains the optical applications of wide-bandgap oxides, which is also the reason why so few oxides enjoy the success of ZnO. Here, using SnO2 as an example, we demonstrate both theoretically and experimentally that UV photoluminescence and electroluminescence can be recovered and enhanced in wide-bandgap oxide thin films with �forbidden� energy gaps by engineering their nanocrystalline structures. In our experiments, the tailored low-temperature annealing process results in a hybrid structure containing SnO2 nanocrystals in an amorphous matrix, and UV emission is observed in such hybrid SnO2 thin films, indicating that the quantum mechanical dipole-forbidden rule has been effectively overcome. Using this approach, we demonstrate the first prototypical electrically pumped UV-light-emitting diode based on nanostructured SnO2 thin films. NPG Asia Materials (2012) 4, e30; doi:10.1038/am.2012.56;published online 9 November 2012

Abstract: Superparamagnetic face-centered cubic (fcc) FePt nanoparticles were synthesized using a polyol process. The effect of reaction temperature and molar ratio of Fe(CO)(5) to Pt(acac)(2) on the structure, composition and morphology of nanoparticles has been investigated. The optimum processing condition has been obtained for producing well-monodisperse fcc-phase FePt nanoparticles with the 2:1 molar ratio of Fe-Pt at 220 A degrees C. In order to circumvent the problem of FePt particle coalescence during high temperature annealing for the L1(0) ordering, FePt nanoparticle/SiO2-matrix composite films have been fabricated by sol-gel method. The experimental results confirm that the amorphous SiO2 matrix effectively inhibits the grain growth and particle aggregation during 700 A degrees C annealing for 1 h. Well-monodisperse face-centered tetragonal (fct) FePt particles embedded in the SiO2 matrix can be obtained with the long-range chemical order parameter S of similar to 0.74, indicating partially ordered L1(0) phase transition in FePt/SiO2 composite films. The FePt/SiO2 system exhibits a hysteretic behavior with smaller coercive field of 1,450 Oe. The incomplete phase transition from cubic deredat height maxsium (A (1)-disordered phase to tetragonal L1(0)-ordered phase) might be responsible for it.

Abstract: Development of advanced electrode materials for Li ion battery (LIB) has attracted great attention due to the demand for portable power sources with higher energy density and higher power density. Transition metal oxides have attracted particular interest due to their low cost, high theoretical capacities and environmentally friendly synthesis processes. However, improvements are still required on their poor capacity retention and unsatisfactory rate performance. Hybridizing metal oxide nanostructures with carbon nanostructures can be an effective route to achieve better Li storage properties by improving the kinetics of charge transfer and alleviating the structural strain during the charge/discharge process. This feature article briefly summarizes our recent research progress on nanostructured hybrids of carbonaceous materials (e.g., amorphous carbon, reduced graphene oxide, and CNT) and metal oxides (e.g., CoO, Fe2O3, V2O5, etc.) in terms of designed synthesis chemistry, understanding the structure-process relationship and development of new types of electrodes.

Abstract: Few layered graphene oxide (GO) nanosheets with large specific surface area (42.1 m(2) g(-1)) are successfully prepared by a modified Hummers method for use as electrodes in the vanadium bromide redox battery. The structure and physicochemical properties of GO are investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Cyclic voltammetry results indicate that GO nanosheets with polymer binder (i.e., polyvinylidiene fluoride (PVDF) or sulfonated poly(ether ether ketone) (SPEEK)) hybrids demonstrate more favorable electrocatalytic activity towards the Br-/Br3- and V3+/V2+ redox couples than the pure graphite. This is attributed to the large numbers of oxygen-containing functional groups on the GO nanosheet surface which can generate more active sites to catalyze the redox reactions. For the binder-based electrodes, the SPEEK based electrode gives the best electrochemical performance (e.g., lower overvoltage for both Br-/Br3- and V3+/V2+ redox couple reactions and higher peak currents for the V3+/V2+ redox couple). (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: FePt nanoparticles (NPs) have been encapsulated in the insulating and protective oxide matrix, using a sol-gel process, in order to prevent particles from agglomerating and sintering during the heat-treatment process required for the L1(0) ordering. The microstructural and ferromagnetic properties of FePt/TiO2 nanocomposites were characterized. The presence of oxide-matrix leads to more homogeneous microstructures and better magnetic properties. The short range positional order of the FePt NPs can be preserved upon annealing at 700 degrees C to possess higher room-temperature coercivities (H-C = 3.7 kOe). Such nanocomposites with assemblies of high-coercivity magnetic nanoparticles are attractive for realizing new types of ultra-high-density data storage devices and magneto-composites. (C) 2012 Elsevier B. V. All rights reserved.

Abstract: Ultrathin metal sulphide nanomaterials exhibit many unique properties, and are thus attractive materials for numerous applications. However, the high-yield, large-scale synthesis of well-defined ultrathin metal sulphide nanostructures by a general and facile wet-chemical method is yet to be realized. Here we report a universal soft colloidal templating strategy for the synthesis of high-quality ultrathin metal sulphide nanocrystals, that is 3.2 nm-thick hexagonal CuS nanosheets, 1.8 nm-diameter hexagonal ZnS nanowires, 1.2 nm-diameter orthorhombic Bi2S3 nanowires and 1.8 nm-diameter orthorhombic Sb2S3 nanowires. As a proof of concept, the ultrathin CuS nanosheets are used to fabricate an electrode for a lithium-ion battery, which exhibits a large capacity and good cycling stability, even after 360 cycles. Furthermore, high-yield, gram-scale production of these ultrathin metal sulphide nanomaterials has been achieved (similar to 100%, without size-sorting process). Our method could be broadly applicable for the high-yield production of novel ultrathin nanostructures with great promise for various applications.

Abstract: Novel CuxS/Cu (1 < x < 2) nanotubes were prepared by a facile wet chemical approach in polyethylene glycol (PEG). Here, Cu nanowires were presynthesized and then converted to nanotubes via a mass diffusion process. A thin PEG layer is physically adsorbed on the nanotube surface. The obtained CuxS/Cu nanotubes show good Li storage properties with stable cyclability upon Li ion insertion/extraction, which is attributed to the existence of the PEG capping and the reduced dissolution of Li polysulfides into the electrolytes. Furthermore, CuxS/Cu nanotubes with 10 wt % Cu show promising rate capabilities (a fifth-cycle discharge capacity of 282 mA h g(-1) at a current density of 5 A g(-1)) due to the enhanced kinetics of charge transfer.

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Abstract: 6,8,15,17-Tetraaza-1.18,4.5,9.10,13.14-tetrabenzoheptacene (TTH, 1) has been prepared and characterized by single-crystal X-ray structure analysis. A phototransistor device based on TTH single crystal demonstrated that TTH showed a good performance in signal amplification under the photoconductive effect as well as photocontrolled switches.

Abstract: A new dye-sensitized solar cell based on a thermoelectric Bi2Te3/TiO2 composite anode is demonstrated, in which the incorporated Bi2Te3 nanoplates function as built-in nanoscale electron generators to convert �waste heat� to electricity and as a good photoreaction catalyst to enhance the charge transfer rate, resulting in 28% improvement of the overall power conversion efficiency.

Abstract: Single-crystalline TiOF2 nanotubes were prepared by a one-step solvothermal method. The nanotubes are rectangular in shape with a length of 23 mu m, width of 200300 nm, and wall thickness of 4060 nm. The formation of TiOF2 nanotubes is directly driven by the interaction between TiF4 and oleic acid in octadecane to form the 1D nanorods, and this is followed by a mass diffusion process to form the hollow structures. The synthesis approach can be extended to grow TiOF2 nanoparticles and nanorods. Compared with TiO2, which is the more commonly considered anode material in lithium-ion batteries, TiOF2 has the advantages of a lower Li-intercalation voltage (e.g., to help increase the total voltage of the battery cell) and higher specific capacities. The TiOF2 nanotubes showed good Li-storage properties with high specific capacities, stable cyclabilities, and good rate capabilities.

Abstract: We report a facile approach to prepare carbon-coated troilite FeS (C@FeS) nanosheets via surfactant-assisted solution-based synthesis. 1-Dodecanethiol is used as both the sulfur source and the surfactant, which may form different-shaped micelles to direct the growth of nanostructures. Under appropriate growth conditions, the iron and sulfur atoms react to form thin layers of FeS while the hydrocarbon tails of 1-dodecanethiol separate the thin FeS layers, which turn to carbon after annealing in Ar. Such an approach can be extended to grow C@FeS nanospheres and nanoplates by modifying the synthesis parameters. The C@FeS nanosheets display excellent Li storage properties with high specific capacities and stable charge/discharge cyclability, especially at fast charge/discharge rates.

Abstract: A crystalline three-dimensional (3D) quaternary chalcohalide, Hg7InS6Cl5 (1), has been synthesized through a solid-state reaction under medium temperature. It is the first example in the family of the Hg-IIIA-Q-X (Q = S, Se, Te; X = F, Cl, Br, I) systems. Compound 1 features a 3D network and has an optical band gap of 2.54 eV.

Abstract: SnSb-carbon nanotube nanocomposites are prepared by mixing melt-spun nanocrystalline SnSb with carbon nanotubes. The composite with 10 wt% acid functionalized CNTs shows a good initial Coulombic efficiency of 79% and a reversible capacity of 860 mAhg(-1) during the 40th cycle at a current density of 160 mAg(-1). Apart from that, the composite also shows promising capacities at high Crates. The enhancement is attributed to the synergistic effect between the nanocrystalline SnSb alloy and the CNT scaffold, which buffers the pulverization process and facilitates fast lithium ions diffusion. (C) 2011 Elsevier B.V. All rights reserved.

Abstract: 1D hierarchical tubular MnO2 nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO2 nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO2 nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO2 nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO2 nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO2 nanostructures prepared, tubular MnO2 nanostructures composed of assembled nanosheets show optimized charge storage performance when tested as supercapacitor electrodes, for example, delivering an power density of 13.33 kW.kg(-1) and a energy density of 21.1 Wh.kg(-1) with a long cycling life over 3000 cycles, which is mainly related to their features of large specific surface area and optimized charge transfer pathway.

Abstract: The manganese oxide-multi-walled carbon nanotube (MnOx/CNT) composite was successfully synthesized following a surface deposition method. Subsequently, the palladium nanoparticles were homogeneously deposited onto this MnOx/CNT hybrid material followed by being reduced under H-2 atmosphere. The catalytic activity in solvent-free benzyl alcohol oxidation was correlated with MnOx loading, indicating the important role of manganese oxide in tuning the properties of Pd catalytic active site, e.g., dispersion and electron density. In the presence of reducible MnOx on CNT, the electron transfer and oxygen activation were greatly enhanced because of the synergistic interaction between Pd metallic nanoparticles and the hybrid support materials. Due to this strong metal support interaction (SMSI), the Pd/MnOx/CNT catalysts were remarkably stable against deactivation. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: A novel solvothermal process was developed for the synthesis of carbon-coated Co9S8 nanodandelions using 1-dodecanethiol as the sulfur source and the soft template. Replacing 1-dodecanethiol with sulfur powder as the sulfur source leads to the formation of 20 nm Co9S8 nanoparticles without carbon coating. When tested as LIB anode, the C@ Co9S8 dandelion delivers a specific capacity of 520 mA h g(-1) at a current density of 1 A g(-1) (1.8 C) during the 50th cycle, which is much higher than that of Co9S8 nanoparticles (e.g. 338 mA h g(-1)). Furthermore, the C@Co9S8 dandelion also exhibits excellent high C-rate performance, e.g., depicts a 10th-cycle capacity of 373 mA h g(-1) at a current density of 6 A g(-1) (10.9 C), which is better than that of many reported anode materials. Such synthesis approach is attractive for the preparation of sulfide anode materials with high Li storage properties.

Abstract: Lithium-ion batteries have been actively researched in recent years due to it being one of the most promising energy storage systems. Herein, we report a novel approach where germanium nanowires (Ge NW) are grown in gold-seeded porous carbon via the solution-liquid-solid mechanism, and the corresponding improvement observed in terms of the specific capacity of this porous carbon-germanium nanowires (PC-Ge NW) composite anode. At a current density of 160 mAg(-1) and voltage window of 0.001-1.5 V. a specific capacity of 789 mAhg(-1) during the 50th cycle for PC-Ge NW is achieved as compared to 624 mAhg(-1) during the 50th cycle for pure Ge NW. Even though the content of the Ge is only 53.5 weight percent in the PC-Ge NW composite, it yields a better stability and higher specific capacity, indicating a synergistic effect between porous carbon and Ge nanowires. There is also potential cost savings since the use of a lower amount of Ge can bring about good cycling properties. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Self-assembled face-centered cubic FePt nanoparticles on Si substrates were embedded into amorphous Al2O3 capping layers with various thicknesses in the range 5-20 nm using atomic layer deposition (ALD) technology. The effect of the Al2O3 layer thickness on the structure, mono-dispersibility, and magnetic properties of the FePt/Al2O3-matrix composite films was investigated. After annealing at 700 degrees C in a reducing atmosphere for 1 h, well-dispersed face-centered tetragonal (fct) FePt particles could be obtained for the samples with 10 nm-thick and greater Al2O3 layers. Experimental results suggest that the protection of the amorphous 10 nm-thick Al2O3 matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L1(0) ordering transition through annealing. The 5 nm fct FePt-nanoparticles/10 nm-thick Al2O3-matrix sample shows higher coercivity of 5.9 kOe. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a potential new approach to fabricate patterned magnetic recording media with ultrahigh areal density.

Abstract: We report a facile approach to synthesize nanocomposites with Fe3O4 nanopaticles (NPs) attached to reduced graphene oxide (rGO) sheets by a solvothermal process, which combines the growth of Fe3O4 NPs and the reduction of GOs in one single step. These Fe3O4/rGO nanocomposites were further used to fabricate thin film supercapacitor electrodes by using a spray deposition technique without the addition of insulating binders. It was found that the Fe3O4/rGO nanocomposites showed much higher specific capacitances than that of either pure rGO or pure Fe3O4 NPs. We further carried out electrochemical characterization of the Fe3O4/rGO nanocomposites with different Fe3O4 : rGO weight ratios (e.g. I-Fe3O4 : rGO) and showed that Fe3O4/rGO nanocomposites with I-Fe3O4 : rGO 2.8 exhibited the highest specific capacitance of 480 F g(-1) at a discharge current density of 5 A g(-1) with the corresponding energy density of 67 W h kg(-1) at a power density of 5506 W kg(-1). These Fe3O4/rGO nanocomposites also showed stable cycling performance without any decrease in the specific capacitance after 1000 charge/discharge cycles.

Abstract: Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied. Unfortunately, surfaces with high reactivity usually diminish rapidly during the crystal growth process as a result of surface energy minimization. The crystal planes of nickel hydroxide play an essential role in determining its catalytic oxidation properties. In this study, beta-Ni(OH)(2) nanocolumns with well-defined crystal planes have been synthesized by a facile solution-based hydrothermal method. TEM and XRD studies reveal that the assembled stacking of the Ni(OH)(2) nanocrystals leads to the predominantly exposed planes as unusually reactive (100) facet rather than the stable (001) facet in the hexagonal nanoslice structures. Consequently, it is demonstrated that the beta-Ni(OH)(2) nanocolumns are more electrochemical catalytic active than their counterparts, nanoslices and nanoplates. The current study indicates that catalysts with well-defined reactive surface can be �designed� through controlled synthesis of nanostructures.

Abstract: We report here a study on the Li ion storage performance of binary phased SnO2/rGO and ternary phased SnO2-Fe2O3/rGO composite nanostructures. The SnO2/rGO and SnO2-Fe2O3/rGO were prepared by a facile wet-chemical approach. The Li storage performances of these samples were closely related to the weight ratio of SnO2 : rGO or SnO2 : Fe2O3 : rGO. It was found that ternary SnO2-Fe2O3/rGO composite nanostructures (e. g. with a weight ratio of SnO2 : Fe2O3 : rGO = 11 : 1 : 13) showed significant enhancement of the specific capacities and cyclabilities as compared to that of SnO2/rGO samples. For example, the SnO2-Fe2O3/rGO electrode depicted a specific capacity of 958 mA h g(-1) at a current density of 395 mA g(-1) (0.5 C) during the 100(th) cycle. Such Li storage performances of the SnO2-Fe2O3/rGO electrodes, especially at high current densities (e.g. 530 mA h g(-1) at 5 C rate), were also much better than those reported for either SnO2-based or Fe2O3-based electrodes. Such a synergetic effect in the SnO2/Fe2O3/rGO composite nanostructures is promising for the development of advanced electrode materials for rechargeable Li-ion batteries.

Abstract: Organic nanowires of 9,10-dibromoanthracene (DBA) and 9,10-dicyanoanthracene (DCNA) were obtained by adding the THF solution of DBA/DCNA into water containing P123 surfactants. The as-prepared nanowires were characterized by UV-vis, fluorescence spectra, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). We found that DBA and DCNA nanowires emitted green light rather than blue light for molecules in THF solution. The red-shift UV and fluorescent spectra of DBA and DCNA nanowires implied that these nanowires were formed through J-aggregation. The photoconducting study of DBA/DCNA nanowire-based network on rGO/SiO(2)/Si shows different photocurrent behaviors upon irradiation, which displayed that electron transfer from DCNA nanowire to rGO was stronger than that of DBA nanowires to rGO.

Abstract: Hydrated vanadium pentoxide (V(2)O(5)center dot 0.44H(2)O, HVO) nanobelts were synthesized by a simply high-yield (e. g. up to similar to 99%) hydrothermal approach. The length of these nanobelts was up to several hundred micrometers while the diameter was only similar to 20 nm and the thickness was similar to 10 nm. Binder-free bulky papers were prepared by using these HVO nanobelts and were tested as Li ion battery cathodes. The unique architecture of the HVO bulky paper provides hierarchical porous channels and large specific surface area, which facilitate fast ion diffusion and effectively strain relaxation upon charge-discharge cycling. The electrochemical tests revealed that the flexible HVO cathode could deliver high reversible specific capacities with similar to 100% Coulombic efficiency, especially at high C rates. For example, it achieved a reversible capacity of 163 mAh g(-1) at 6.8 C.

Abstract: Reduced graphene oxide (rGO) supported highly porous polycrystalline V2O5 spheres (V2O5/rGO) were prepared by using a solvothermal approach followed by an annealing process. Initially, reduced vanadium oxide (rVO) nanoparticles with sizes in the range of 10-50 nm were formed through heterogeneous nucleation on rGO sheets during the solvothermal process. These rVO nanoparticles were oxidized to V2O5 after the annealing process in air at 350 degrees C and assembled into polycrystalline porous spheres with sizes of 200-800 nm. The weight ratio between the rGO and V2O5 is tunable by changing the weight ratio of the precursors, which in turn affects the morphology of V2O5/rGO composites. The V2O5/rGO composites display superior cathode performances with highly reversible specific capacities, good cycling stabilities and excellent rate capabilities (e.g. 102 mA h g(-1) at 19 degrees C).

Abstract: We report an environment-friendly approach to synthesize transition metal oxide nanoparticles (NPs)/reduced graphene oxide (rGO) sheets hybrids by combining the reduction of graphene oxide (GO) with the growth of metal oxide NPs in one step. Either Fe(2)O(3) or CoO NPs were grown onto rGO sheets in ethanol solution through a solvothermal process, during which GOs were reduced to rGO without the addition of any strong reducing agent, e.g. hydrazine, or requiring any post-high-temperature annealing process. The GO or rGO during the precipitation of metal oxide NPs may act as heterogeneous nucleation seeds to facilitate the formation of small crystal grains. This may allow more efficient diffusion of Li ions and lead to high specific capacities. These metal oxide NPs-rGO hybrids were used as anodes for Li-ion batteries, which showed high capacities and excellent charge-discharge cycling stability in the voltage window between 0.01 and 3.0 V. For example, Fe(2)O(3) NPs/rGO hybrids showed specific capacity of 881 mA h g(-1) in the 90(th) cycle at a discharge current density of 302 mA g(-1) (0.3 C), while CoO NPs/rGO hybrids showed a lower capacity of 600 mA h g(-1) in the 90(th) cycle at a discharge current density of 215 mA g(-1) (0.3 C). These nanohybrids also show excellent capacities at high C rate currents, e.g. 611 mA h g(-1) for Fe(2)O(3)/rGO sample in the 300(th) cycle at 2014 mA g(-1) (2 C). Such synthesis technique can be a promising route to produce advanced electrode materials for Li-ion batteries.

Abstract: ZnSb nanotubes were grown through a template free electrodeposition method under over-potential conditions. The growth of the nanotubes was attributed to the template effect from H(2) bubbles. Due to their hollow structure, the ZnSb nanotubes depicted better Li ion storage performance compared to that of ZnSb nanoparticles deposited under different conditions.

Abstract: A facile chemical approach has been developed to produce nanohybrids with ultrathin Co oxides nanowall arrays on reduced graphene oxide (rGO) sheets. The Co oxides exhibited porous structure. The porosity of the Co oxide/rGO nanohybrids and the grain size of the Co oxides could be tailored by varying the annealing temperature, which directly affected their performance as Li-ion battery electrodes. When tested as anode materials for Li-ion batteries, these Co oxide/rGO nanohybrids showed structural-process-dependent performances. For example, Co(3)O(4)/rGO hybrids obtained by annealing alpha-Co(OH)(2)/rGO at 350 degrees C showed a high specific capacity of 673 mAh g(-1) after 100 cycles at a discharge current density of 180 mA g(-1) (0.2 C), which was better than Co(3)O(4)/rGO samples obtained at other annealing temperatures. CoO/rGO hybrids obtained by pyrolysis of alpha-Co(OH)(2)/rGO at 350 degrees C showed optimum performance, as compared to that of CoO/rGO samples obtained at other annealing temperatures, with a capacity of 732 mAh g(-1) after 100 cycles at a discharge current density of 150 mA g(-1) (0.2 C). Although many metal oxide/rGO hybrid systems have been investigated as electrode materials for Li-ion batteries, this study indicates that optimization of such nanohybrids by adjusting the phases, grain sizes, and porosities is necessary to achieve ideal Li storage performances.

Abstract: A stable aqueous dispersion of hydrophobic single-walled carbon nanotubes (SWCNTs) and amphiphilic graphene oxide (GO) nano-sheets was produced by sonication mixing without assistance of any surfactant. Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electrical characterization suggest that SWCNTs are completely wrapped by GO nano-sheets. The spontaneous formation of such a core-shell structure is due to the strong pi-pi stacking interaction between the two materials. The electronic coupling between them is evidenced by time-resolved fluorescence measurement. The potential of such a nanocarbon hybrid in optical limiting and supercapacitor applications is discussed. (C) 2011 Elsevier Ltd. All rights reserved.

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Abstract: We demonstrate a simple, efficient, yet versatile method for the realization of core-shell assembly of graphene around various metal oxide (MO) nanostructures, including nanowires (NWs) and nanoparticles (NPs). The process is driven by (i) the ring-opening reaction between the epoxy groups and amine groups in graphene oxide (GO) platelets and amine-modified MO nanostructures, respectively, and (ii) electrostatic interaction between these two components. Nearly every single NW or NP is observed to be wrapped by graphene. To the best of our knowledge, this is the first report that substrate-supported MO NWs are fully coated with a graphene shell. As an example of the functional properties of these compound materials, the graphene@alpha-Fe(2)O(3) core shell NPs are investigated as the lithium-ion battery (LIB) electrode, which show a high reversible capacity, improved cycling stability, and excellent rate capability with respect to the pristine alpha-Fe(2)O(3). The superior performance of the composite electrode is presumably attributed to the effectiveness of the graphene shell in preventing the aggregation, buffering the volume change, maintaining the integrity of NPs, as well as improving the conductivity of the electrode.

Abstract: Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

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Abstract: In this work, we prepared few-layered graphene (FLG) films and investigated their thermoelectric properties. It was found that pristine FLG films showed a low thermopower of similar to 40 mu V/K. We further processed these FLG films by attaching them with 1,1�-azobis(cyanocyclohexane) or 1,3,6,8-pyrenetetrasulfonic acid. The thermopower of FLG films with attached molecules increased to above similar to 180 mu V/K. Such enhancement in the thermopower led to an increase in their power factor by more than 4.5 times. Theoretical investigation indicated that a potential difference can be introduced between the outer layer and inner layer of FLG films upon molecule attachments. Simulation of the thermopower based on Kubo�s formula provided qualitative support to our experimental results.

Abstract: The nucleation mechanism of electrochemical deposition of Cu on reduced graphene oxide (rGO) electrodes has been systematically studied on the basis of the cyclic voltammetry, Tafel plot, and chronoamperometry. Our results show that the experimental parameters including electrolyte concentration, deposition potential, solution pH, and the presence of background electrolyte can determine the nucleation mechanism. Scanning electron microscopy is employed to study the nucleation and growth of Cu on rGO electrodes. This study is significant in development of the electrochemical method in practical applications based on the rGO electrodes.

Abstract: In this work, we show that the maximum thermopower of few layers graphene (FIG) films could be greatly enhanced up to similar to 700 mu V/K after oxygen plasma treatment. The electrical conductivities of these plasma treated FIG films remain high, for example, similar to 10(4) S/m, which results in power factors as high as similar to 4.5 x 10(-3) W K(-2) m(-1). In comparison, the pristine FLG films show a maximum thermopower of similar to 80 mu V/K with an electrical conductivity of similar to 5 x 10(4) S/m. The proposed mechanism Is due to generation of local disordered carbon that opens the band gap. Measured thermopowers of single-layer graphene (SLG) films and reduced graphene oxide (rGO) films were in the range of -40 to 50 and -10 to 20 mu V/K, respectively. However, such oxygen plasma treatment is not suitable for SLG and rGO films. The SIG films were easily destroyed during the treatment while the electrical conductivity of rGO films is too low.

Abstract: We report a simple wet-chemical process to prepare porous CuO nanobelts (NBs) with high surface area and small crystal grains. These CuO NBs were mixed with carbon nanotubes in an appropriate ratio to fabricate pseudocapacitor electrodes with stable cycling performances, which showed a series of high energy densities at different power densities, for example, 130.2, 92, 44, 25, and 20.8 W h kg(-1) at power densities of 1.25, 6.25, 25, and 50 k Wh kg(-1), respectively. CuO-on-single-walled carbon nanotube (SWCNT) flexible hybrid electrodes were also fabricated using the SWCNT films as current collectors. These flexible electrodes showed much higher specific capacitance than that of electrodes made of pure SWCNTs and exhibited more stable cycling performance, for example, effective specific capacitances of >62 F g(-1) for the hybrid electrodes after 1000 cycles in 1 M LiPF6/EC:DEC at a current density of 5 A g(-1) and specific capacitance of only 23.6 F g(-1) for pure SWCNT electrodes under the same testing condition.

Abstract: A single-step fabrication of ZnSb nanostructures using template-free electrochemical deposition was developed. Results have indicated that ZnSb nanoflakes, nanowires, or nanoparticles with controlled composition could be obtained by adjusting the precursor concentration, applied voltage, and substrate type. The ZnSb nanostructures deposited on Cu foils were directly used as Li-ion battery anodes without the addition of any binder. Electrochemical analyses revealed that the interconnected ZnSb nanoflakes depicted high discharge capacities and a stable performance, which were better than that of ZnSb nanowires and nanoparticles. With an initial discharge capacity of 735 mA h/g and an initial Columbic efficiency of 85%, the ZnSb nanoflakes maintained a discharge capacity of 500 mA h/g with a Coulombic efficiency of 98% after 70 cycles at a current density of 100 mA/g (0.18 C). The ZnSb nanowires and nanoparticles showed a capacity of 190 and 40 mA h/g, respectively, after 70 cycles at the same current density. The improved performance of the interconnected ZnSb nanoflakes is attributed to their open structure, with a large surface area and small crystal grains, to facilitate the diffusion of Li ions and to buffer the large volume swings during the lithium intercalation process.

Abstract: n-Type Bi2Te3 nanocomposites with enhanced figure of merit, ZT, were fabricated by a simple, high-throughput method of mixing nanostructured Bi2Te3 particles obtained through melt spinning with micron-sized particles. Moderately high power factors were retained, while the thermal conductivity of the nanocomposites was found to decrease with increasing weight percent of nanoinclusions. The peak ZT values for all the nanocomposites were above 1.1, and the maximum shifted to higher temperature with increasing amount of nanoinclusions. A maximum ZT of 1.18 at 42A degrees C was obtained for the 10 wt.% nanocomposite, which is a 43% increase over the bulk sample at the same temperature. This is the highest ZT reported for n-type Bi2Te3 binary material, and higher ZT values are expected if state-of-the-art Bi2Te3-x Se (x) materials are used.

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Abstract: Sb based alloy nanostructures have attracted much attention due to their many promising applications, e. g. as battery electrodes, thermoelectric materials and magnetic semiconductors. In many cases, these applications require controlled growth of Sb based alloys with desired sizes and shapes to achieve enhanced performance. Here, we report a flexible catalyst-free chemical vapor deposition (CVD) process to prepare Cu-Sb nanostructures with tunable shapes (e. g. nanowires and nanoparticles) by transporting Sb vapor to react with copper foils, which also serve as the substrate. By simply controlling the substrate temperature and distance, various Sb-Cu alloy nanostructures, e. g. Cu(11)Sb(3) nanowires (NWs), Cu(2)Sb nanoparticles (NPs), or pure Sb nanoplates, were obtained. We also found that the growth of Cu(11)Sb(3) NWs in such a catalyst-free CVD process was dependent on the substrate surface roughness. For example, smooth Cu foils could not lead to the growth of Cu(11)Sb(3) nanowires while roughening these smooth Cu foils with rough sand papers could result in the growth of Cu(11)Sb(3) nanowires. The effects of gas flow rate on the size and morphology of the Cu-Sb alloy nanostructures were also investigated. Such a flexible growth strategy could be of practical interest as the growth of some Sb based alloy nanostructures by CVD may not be easy due to the large difference between the condensation temperature of Sb and the other element, e. g. Cu or Co.

Abstract: In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH-) while photo-generated holes oxidize CdSe to Cd(2+) and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH = 10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).

Abstract: CuInSe2 (CIS) nanodandelion structures were synthesized by a two-step solvothermal approach. First, InSe nanodandelions were prepared by reacting In(acac)(3) with trioctylphosphine-selenide (TOP-Se) in 1-octadecene (ODE) at 170 degrees C in the presence of oleic acid. These InSe dandelions were composed of polycrystalline nanosheets with thickness < 10 nm. The size of the InSe dandelions could be tuned within the range of 300 nm-2 mu m by adjusting the amount of oleic acid added during the synthesis. The InSe dandelion structures were then reacted with Cu(acac)(2) in the second-step solvothermal process in ODE to form CIS nanodandelions. The band gap of the CIS dandelions was determined from ultraviolet (UV) absorption measurements to be similar to 1.36 eV, and this value did not show any obvious change upon varying the size of the CIS dandelions. Brunauer-Emmett-Teller (BET) measurements showed that the specific surface area of these CIS dandelion structures was 44.80 m(2) g(-1), which was more than five times higher than that of the CIS quantum dots (e.g. 8.22 m(2) g(-1)) prepared by using reported protocols. A fast photoresponsive behavior was demonstrated in a photoswitching device using the 200 nm CIS dandelions as the active materials, which suggested their possible application in optoelectronic devices.

Abstract: We report the synthesis of a series of monodispersed Bi-doped PbTe nanocrystals with tunable morphologies by using a doping precursor of bismuth(III) 2-ethylhexanoate. The as-synthesized Pb(1-x)Bi(x)Te (x = 0.005, 0.010, 0.015, 0.020) nanocrystals are characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Hall measurements. The nanocrystals with controlled spherical, cuboctahedral, and cubic shapes were readily prepared by varying the Bi doping concentration. Thermoelectric investigation of these nanocrystals shows that the Bi(3+) doping increases electrical conductivity from 350 to 650 K and changes the Seebeck coefficient sign from positive to negative.

Abstract: In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

Abstract: Nanostructured thermoelectric semiconductors represent a promising new direction that can further increase energy conversion efficiency, which requires the realization of thermoelectric nanocrystals with size comparable to their de Broglie wavelength while maintaining a high electrical conductivity. Here, we demonstrate a new facile process to grow self-assembled Sb2Te3 nanoparticles with controlled particle size and enhanced thermoelectric properties by using a catalyst-free vapor transport growth technique. The samples show much more enhanced Seebeck coefficients than that of bulk Sb2Te3 with similar charge carrier concentration. Meanwhile, the thermal conductivity measurements with pulse photothermal reflectance suggest that the these Sb2Te3 nanoparticle films show much reduced thermal conductivity as compared to that of bulk Sb2Te3. The discussed approach is promising for realizing new types of highly efficient thermoelectric semiconductors.

Abstract: The influence of deposition conditions on the microstructure of Ca3Co4O9 (CCO) thin films fabricated by the pulsed laser deposition technique was investigated. X-ray diffraction revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca (x) CoO2 secondary phase. The Ca (x) CoO2 structure was further confirmed by high-resolution transmission electron microscopy. The CCO thin-film growth was deduced to be a kinetically controlled process, and the quality of the thin films strongly depended on the coalescence process. The formation of Ca (x) CoO2 was inevitable during the thin-film growth. However, given enough time and supply of oxygen at a lower deposition rate, it was possible to transform the Ca (x) CoO2 phase into the desired CCO phase during the coalescence process, while with faster deposition, more Ca (x) CoO2 structure was formed, and the secondary phase could hardly transform into the CCO phase.

Abstract: Nanostructured Sb was prepared through a simple polyol process. Either Sb nanoparticles (Sb NP) or nanowires (Sb NW) were obtained by adjusting the concentration of surfactant. Electrochemical analyses revealed that the resultant Sb crystals displayed high charge storage capacities as Li-ion battery electrodes and relatively poor cycling retention during the charge discharge process. For instance, the capacity was 560-584 mA h/g during the second cycle, which decreased to 120-200 mA h/g during the 70th cycle at a rate of 0.2 C. Thus, Sb NPs were reacted with Co precursors to form one-dimensional (I-D) NP chains wrapped in a polyvinyl pyridine layer, and the length of the NP chains could be adjusted by varying the concentration of polyvinyl pyridine. Through a controlled annealing process, the polyvinyl pyridine layer was converted to amorphous carbon, which led to the formation of 1-D core shell structures with CoSb3 NP chains entrapped in the carbon layer. Although CoSb3 NP chains with a carbon shell displayed a lower initial charge storage capacity than Sb nanostructures, improved cycling performance was observed. The capacity was 468 mA h/g during the second cycle, which dropped to 421 mA h/g during the 70th cycle at a rate of 0.2 C. Compared to CoSb3 produced via other techniques, CoSb3/C NP chains displayed higher cycling stability, because of the presence of a carbon buffer layer.

Abstract: Ca3-xBixCo4O9 (x=0-0.4) thin films were deposited on single-crystal sapphire (0001) substrates by pulsed laser deposition. Structural characterizations indicated that these thin films exhibited perfect c-axis orientation and were well crystallized. Surface chemical states analysis confirmed Bi-substitution for Ca in the thin films with x < 0.4. For the thin film with x=0.4, excessive Bi were found isolated within the film. Due to their perfect orientation, in-plane electrical properties of these thin films measured from 300 to 740 K were found to be comparable to those of the single crystals. Furthermore, Bi-substitution was noted for the reduced electrical resistivity and enhanced Seebeck coefficient. The above superior properties resulted in a high power factor of 0.81 mW m(-1) K-2 at 740 K for thin film Ca2.7Bi0.3Co4O9, which was about 29% improvement as compared to that of pure Ca3Co4O9 thin film. The results suggested that Bi-doped Ca3Co4O9 thin films could be a promising candidate for thermoelectric applications at elevated temperatures. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3499324]

Abstract: Copper Indium diselenide (CIS) nanocrystals were synthesized by a new room-temperature reverse microemuslion route. By changing the water to surfactant ratio, the size of the particles can be readily adjusted while the composition of the particles can be tuned by changing the precursor ratio. The UV-visible absorption and photoluminescence spectra show blue shift for CIS particles with smaller size. The corresponding band gaps of the as-prepared CIS particles are similar to 2 eV, which is larger than that of bulk CIS.

Abstract: We report a facile way to grow various porous NiO nanostructures including nanoslices, nanoplates, and nanocolumns, which show a structure-dependence in their specific charge capacitances. The formation of controllable porosity is due to the dehydration and re-crystallization of beta-Ni(OH)(2) nanoplates synthesized by a hydrothermal process. Thermogravimetric analysis shows that the decomposition temperature of the beta-Ni(OH)(2) nanostructures is related to their morphology. In electrochemical tests, the porous NiO nanostructures show stable cycling performance with retention of specific capacitance over 1000 cycles. Interestingly, the formation of nanocolumns by the stacking of beta-Ni(OH)(2) nanoslices/plates favors the creation of small pores in the NiO nanocrystals obtained after annealing, and the surface area is over five times larger than that of NiO nanoslices and nanoplates. Consequently, the specific capacitance of the porous NiO nanocolumns (390 F/g) is significantly higher than that of the nanoslices (176 F/g) or nanoplates (285 F/g) at a discharge current of 5 A/g. This approach provides a clear illustration of the process-structure-property relationship in nanocrystal synthesis and potentially offers strategies to enhance the performance of supercapacitor electrodes.

Abstract: We demonstrate a facile colloidal method for synthesizing Janus nanoparticles, whose eccentric polymer shells are exploited to fabricate eccentric bimetallic cores.

Abstract: A facile route for the generation of the dual patterns of metal oxide nanomaterials, for example, ZnO and CuO, has been developed by printing the oxide seeds through a combination of microcontact printing (mu CP) and microfluidic (mu F) techniques, followed by the simultaneous growth of the two metal oxide nanomaterials in a one-step solution reaction based on hydrothermal, seed-mediated selective growth. The obtained dual patterns of ZnO nanorods and CuO nanoneedles show a sharp boundary between them, indicating well-defined dual-pattern generation. Also, the simultaneous growth of metal oxide nanomaterials is highly material-selective for the specific seeds prepatterned on substrates, resulting in the selective growth of ZnO nanorods and CuO nanoneedles on the ZnO and CuO seeds, respectively. Moreover, the generation of high-quality dual patterns has been similarly realized on a flexible poly(ethylene terephthalate) (PET) wafer. This study demonstrates the well-controlled hydrothermal growth of different metal oxide nanomaterials in the same reaction solution on the preprinted oxide seeds on the target substrates. It opens up an avenue to develop multifunctional devices of different metal oxides with the combination of mu CP and mu F techniques.

Abstract: B-site modification lead strontium zirconate titanate Pb(0.4)Sr(0.6)Zr(x)Ti(1-x)O(3) (PSZT, x=0-0.7) thin films were prepared on Pt/TiO(2)/SiO(2)/Si substrates by a sol-gel method. The XRD results indicate that paraelectric PSZT thin films at room temperature are obtained as x approaches 0.2. The temperature-dependent dielectric and hysteresis loop measurements reveal that the thin films have diffuse phase transition characteristics and relaxor-like behavior with nano-polar regions in the paraelectric films at room temperature. The Curie temperature of the PSZT thin films varies with the Zr contents, exhibiting a complex trend. This can be attributed to two competitive factors: higher mobility of Ti(4+) than Zr(4+) and smaller open space left for the displacement of Ti ions with the increase of Zr content. The further increase of the Zr contents leads to the simultaneous decrease of dielectric constant, dielectric loss and tunability. PSZT (x=0.4) thin film shows the largest figure of merit of 24.3 with a moderate tunability of 55.8% and a dielectric loss of 0.023. This suggests that B-site ions have different roles in modifying the electrically tunable performance of PSZT thin films for tunable microwave device applications. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: We report enhanced figure of merit, ZT, in p-type Bi0.4Sb1.6Te3 nanocomposites fabricated by a rapid and high throughput method of mixing nanostructured Bi0.4Sb1.6Te3 particles obtained through melt spinning with micronsized particles obtained via solid state reaction. Due to effective scattering of phonons over a wide wavelength spectrum, low thermal conductivity, and moderately good power factor were obtained in the nanocomposites to achieve ZT above 1.5 at room temperature. A maximum ZT of 1.80 was attained at 43 degrees C for the nanocomposite consisting 40 wt % nanoinclusions. This was a 56% increment over the bulk sample, and the highest ZT reported for Bi2Te3-based materials. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427427]

Abstract: Pd monometallic and Au-Pd bimetallic catalysts supported on surface-functionalized SBA-16 were prepared by a conventional adsorption method and were examined using X-ray diffraction, nitrogen physisorption, UV-vis spectroscopy, and high-resolution transmission microscopy. SBA-16 with the unique �super-cage� structure effectively controlled the formation of dispersed noble metal nanoparticles in the mesoporous channels. These confined nanoparticles with a narrow particle size distribution exhibited excellent catalytic activity in the solvent-free benzyl alcohol selective oxidation with molecular oxygen. Amine-functionalization remarkably improved the selectivity towards benzaldehyde. Au-Pd bimetallic catalysts showed enhanced catalytic performance compared to the Au and Pd monometallic catalysts. The highest turnover frequency of 8667 h(-1) was achieved over a bimetallic catalyst with Au:Pd molar ratio of 1:5; this good catalytic activity can be maintained after five recycling runs. The characterization results of scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed that the bimetallic catalyst was constructed of uniformly alloyed nanoparticles with Pd cluster-on-Au cluster structure. The synergetic effect between Au and Pd nanocluster was suggested to account for the better catalytic activity of bimetallic catalysts because the size-dependent effect can be ruled out due to the effective confinement of noble metal nanoparticles by SBA-16 mesostructure. (C) 2010 Elsevier B.V. All rights reserved.

Abstract: A novel dendrimer-templating method for the synthesis of CuO nanoparticles and the in situ construction of ordered inorganic-organic CuO-G2Td(COOH)(16) rice-shaped architectures (RSAs) with analogous monocrystalline structures are reported. The primary CuO nanoparticles are linked by the G2Td(COOH)(16) dendrimer. This method provides a way to preserve the original properties of primary CuO nanoparticles in the ordered hybrid nanomaterials by using the 3D rigid polyphenylene dendrimer (G2Td(COOH)(16)) as a space isolation. The primary CuO nanoparticles with diameter of (6.3 +/- 0.4) nm are synthesized via four successive reaction steps starting from the rapid reduction of Cu(NO(3))(2) by using NaBH(4) as reducer and G2Td(COOH)16 as surfactant. The obtained hybrid CuO-G2Td(COOH)(16) RSA, formed in the last reaction step, possesses a crystal structure analogous to a monocrystal as observed by transmission electron microscopy(TEM). In particular, the formation process of the RSA is monitored by UV-vis, TEM, and X-ray diffraction. Small angle X-ray scattering and Fourier transform infrared I spectroscopy are used to investigate the role of the dendrimer in the RSA formation process. The obtained results illuminate that Cu(2+)-COO(-) coordination bonds play an indispensable role in bridging and dispersing the primary CuO nanoparticles to induce and maintain the hybrid RSA. More importantly, the RSA is retained through the Cu(2+)-COO(-)coordination bonds even with HCl treatment, suggesting that the dendrimers and Cu(2+) ions may form rice-shaped polymeric complexes which could template the assembly of CuO nanoparticles towards RSAs. This study highlights the feasibility and flexibility of employing the peculiar dendrimers to in-situ build up hybrid architectures which could further serve as templates, containers or nanoreactors; for the synthesis of other nanomaterials.

Abstract: CoSb3 nanocomposites with different contents of CoSb3 nanoparticles were prepared by mixing nanosized CoSb3 particles obtained via polyol method and micron-sized particles obtained via solid state reaction. X-ray diffractometer and field emission scanning electron microscope were used to characterize the prepared products. The thermoelectric properties of the nanocomposites with different amounts of nanoparticles as dispersants were measured from room temperature to around 500 degrees C. Due to the grain boundaries scattering, the lattice thermal conductivity was observed to decrease as the amount of nanoparticles increased. The electrical properties were also improved by the addition of nanoparticles. The ZT value of the nanocomposites with 10 wt % of nanoparticles was nearly doubled that of the sample without any nanoparticles.

Abstract: The effects of deposition rate on the microstructure and thermoelectric (TE) properties Of Ca3Co4O9 thin films fabricated by pulsed laser deposition (PLD) technique were investigated. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the CaxCoO2 secondary phase. Formation of CaxCoO2 was inevitable during the thin film growth, and this was discussed from both structural and compositional point of view. With longer deposition interval or with sufficient oxygen at a lower deposition rate, the CaxCoO2 phase was able to transit into the desired Ca3Co4O9 phase during the coalescence process. The quality of the thin films was further analyzed by electrical properties measurements. The Ca3Co4O9 thin film fabricated at a slower deposition rate was found to exhibit a low electrical resistivity of 9.4 m Omega cm and high Seebeck coefficient of 240 mu V/K at about 700 degrees C, indicating a good quality film. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: A straightforward one-step chemical method to in situ synthesis of Ag nanoparticles (Ag NPs) on single-layer graphene oxide (GO) and reduced graphene oxide (r-GO) surfaces is proposed. After simply heating the single-layer GO or r-GO adsorbed on 3-aminopropyltriethoxysilane (APTES)-modified Si/SiOx substrates in a silver nitrate aqueous solution at 75 degrees C, Ag NPs are synthesized and grow on the GO or r-GO surface. The obtained Ag NPs are investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Our method is unique and important since no reducing agent is required in the reaction. Au NPs on a GO surface are obtained by simply immersing the obtained Ag NPs on the GO surface in HAuCl(4) solution.

Abstract: Binary-phased PbTe-PtTe2 nanoparticles are synthesized by co-precipitation in a chemical process. These nanoparticles show much enhanced power factors as compared to that of pure PbTe nanoparticles, which may give impact on development of new types of highly efficient thermoelectric materials.

Abstract: FePt-PtTe2 two phase nanorods have been produced by a polyol process. The shape and magnetic properties of two phase nanorods with different phase ratio are investigated. L1(0) phase transformation of FePt in the nanorods has been accomplished at annealing temperature as low as 400 degrees C with H-c above 500mT. High temperature annealing causes the disintegration of the nanorods due the melting/evaporation of Te element.

Abstract: In this work, uniform SnO2 hollow nanospheres with large void space have been synthesized by a modified facile method. The void space can be easily controlled by varying the reaction time. The formation of interior void space is based on an inside-out Ostwald ripening mechanism. More importantly, this facile one-pot process can be extended to fabricate rattle-type hollow structures using alpha-Fe2O3@SnO2 as an example. Furthermore, the electrochemical lithium storage properties have been investigated. It is found that alpha-Fe2O3@SnO2 nanorattles manifest a Much lower initial irreversible loss and higher reversible capacity compared to SnO2 hollow spheres. This interesting finding supports a general hypothesis that a synergistic effect between functional core and shell materials can lead to improved lithium storage capabilities.

Abstract: A novel photocatalyst ZnTiO3 powder was prepared by a modified alcoholysis method, using ethylene glycol as reagent/solvent and acetylacetone as stabilizer. A series of analytical techniques were used to characterize the crystallinity, composition, bandgap, morphology, specific surface area and grain size of ZnTiO3 powders. The relationship between the physicochemical property and the photocatalytic activity was deeply investigated, too. it is found that the photocatalytic activity is dependent on the phase of catalysts. The product of ZnTiO3 with pure hexagonal-phase calcined at 800 degrees C for 3 h exhibits the maximum photocatalytic performance in the photochemical degradation of the azo dye methyl violet under solar light irradiation. The processing parameters such as the concentration of catalysts and the pH value also play an important role in tuning the photocatalytic activity. The optimal concentration and pH value of the pure hexagonal-phase ZnTiO3 is around 4 g/L and 8 in a 10 mg/L dye-aqueous solution, respectively. (c) 2009 Elsevier B.V. All rights reserved.

Abstract: Selenium Cc carbon core-shell spheres have been synthesized via a simple one-step hydrothermal carbonization process using sucrose and sodium selenite as precursors. Metal selenide or noble metal, e.g. Ag2Se or Au, can be easily encapsulated into the carbon shell by using the as-prepared Se@C core-shell samples as site templates, The transformation from core/shell to yolk/shell structure, e.g, Se@C, Au/Se@C and Ag2Se@C, can be achieved through thermal evaporation under electron beam irradiation or vacuum annealing to evaporate Se. The optical absorption of the samples can be tuned by varying the structure/compositions of the samples.

Abstract: The ability to process assemblies using thin film techniques in a scalable fashion would be a key to transmuting the assemblies into manufacturable devices. Here, we embed FePt nanoparticle assemblies into a silica thin film by sol-gel processing. Annealing the thin film composite at 650. C transforms the chemically disordered fcc FePt phase into the fct phase, yielding magnetic coercivity values H(c) > 630 mT. The positional order of the particles is retained due to the protection offered by the silica host. Such films with assemblies of high-coercivity magnetic particles are attractive for realizing new types of ultra-high-density data storage devices and magneto-composites.

Abstract: The thermoelectric properties of double-filled skutterudites Ca0.1CexCo4Sb12 (x = 0.05, 0.10 and 0.15) were investigated at temperatures ranging from 300 to 775 K. The results showed that the addition of Ca and Ce as filler atoms into CoSb3 led to a substantial decrease in lattice thermal conductivity. The minimum lattice thermal conductivity of 2.76 WK-1 m(-1) was observed in the sample Ca0.1Ce0.15Co4Sb12 at 323 K. This is a 69% reduction as compared with pristine CoSb3. Moreover, filling the voids of the skutterudite crystal lattice with Ca and Ce atoms led to a transition from semiconducting-like behaviour (i. e. d rho/dT < 0) to metallic behaviour (i. e. d rho/dT > 0) as well as a change in the sign of the Seebeck coefficient. The highest dimensionless figure of merit, ZT, was obtained for the sample Ca0.1Ce0.15Co4Sb12. Specifically, it reached ZT of 0.83 at 677 K, which is double that of single-filled Ca0.2Co4Sb12 reported in the literature.

Abstract: Branched core/shell bismuth telluride/bismuth sulfide nanorod heterostructures are prepared by using a biomimetic surfactant, L-glutathionic acid. Trigonal nanocrystals of bismuth telluride are encapsulated by nanoscopic shells of orthorhombic bismuth sulfide. Crystallographic twinning causes shell branching. Such heteronanostructures are attractive for thermoelectric power generation and cooling applications.

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Abstract: Rod-shaped assemblies of FePt nanoparticles embedded amidst PtTe2 nanoplatelets, formed by co-precipitation in the presence of sucrose and trioctylphosphine oxide. The (001.) planes in each of the PtTe2 nanoplatelets are stacked along directions close to the nanorod axis. Separate precipitation of FePt or PtTe2 under identical conditions yield spheres or randomly shaped clusters platelets, underscoring the key influence of co-precipitation on the morphology of the nanostructure assembly. [GRAPHICS]

Abstract: Aluminum-substituted yttrium. iron garnet (Al-YIG) nanostructured powders were synthesized using a citrate-nitrate gel combustion process. Atmospheric plasma-spray (APS) technique was employed to spray deposit the combustion derived feedstock powders. Nevertheless incongruently melting YIG resulted into a two-phase microstructure, Al-YIG powder resulted into a nanostructured garnet single phase when sprayed through thermal plasma. Room temperature saturation magnetization (Ms) and Curie temperature (Tc) of the Al-YIG powders decreased as a function of increasing Al content. As-sprayed YFe3.8Al1.2O12 coating has a room temperature M-s of 6.2 emu/cc and is increased to 7.3 emu/cc after post-deposition heat treatment at 1000 degrees C/1 h. Microstructural characteristics of single splats were analyzed in order to understand the feedstock effect on deposit. (C) 2007 Elsevier B.V. All fights reserved.

Abstract: We demonstrate a new, flexible, one-step approach to direct the synthesis of FePt nanoparticle clusters or Fe3O4 nanoparticles, and their assembly into molecularly interconnected chains without the use of inorganic templates. The chain length as well as the diameter of the nanoparticle cluster can be varied by modifying the surfactants-precursor ratio.

Abstract: Yttrium iron garnet (YIG) coatings were prepared using a liquid precursor plasma spray (PPS) method. Regular and reverse coprecipitated feedstock sols were directly sprayed through a radio frequency (RF) plasma torch. X-ray diffraction (XRD) analyses revealed the formation of amorphous coating in the as-sprayed condition. Post-annealing treatments resulted into nanostructured garnet coatings and the crystallinity of the coatings increased as a function of increasing annealing temperature. Coating annealed at 1000 degrees C/h exhibited a saturation magnetization of 65 emu/cc and a coercivity of 37 Oe. PPS approach feeds on molecularly mixed precursor liquids or sols, obviating the need for pre-mixed powders and thus opening up new avenues for developing nanostructured magnetic oxide coatings. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Abstract: A microemulsion approach to obtain high-coercivity (850 mT) FePt nano-magnets capped with a nanoscopic silica shell is reported (see figure). versatile method allows the easy tuning of particle size and composition. The silica shell inhibits agglomeration and preserves the chemical stability of the particles up to 650 degrees C, and facilitates surface functionalization and particle assembly. These attributes are attractive for harnessing the nanomagnets for realizing novel devices and composites.

Abstract: Sb-doped FePt nanoparticles with an average diameter of 8.5 nm were prepared by thermal decomposition of platinum acetylacetonate, antimony acetate, and iron pentacarbonyl. Upon annealing to similar to 300 degrees C for 30 min, nanoparticles with X-Sb=0.14 and 0.23 show H-c>500 mT, and L1(0) ordering parameter S values of similar to 0.83-0.87. Transmission electron microscopy of the annealed assemblies shows no observable nanoparticle coalescence at 300 degrees C. Low-temperature coercivity measurements with a superconducting quantum interference device indicate the presence of particles that exhibit superparamagnetism, probably due to the large particle size distribution or inhomogeneity in Sb incorporation. Our results underscore the necessity to synthesize monodisperse FePt nanoparticles with controlled composition to maximize ferromagnetic behavior. (C) 2006 American Institute of Physics.

Abstract: The coercivity of the plasma-sprayed MnZn ferrite films decreases significantly after annealing in air at the temperature range of 500-800 degrees C. Magnetostriction and surface stress changes incurred in these ferrite films after the annealing process has been measured. It is found that the effects of the external stress on the magnetic properties of the plasma-sprayed MnZn ferrite films are minor. The coercivity mechanism arising from the magnetoelastic effects due to the nonzero magnetostriction has been analyzed to be small and is not dominant in controlling the magnetization process in these ferrite films. (c) 2005 American Institute of Physics.

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Abstract: The magnetic properties of MnZn ferrites are affected by the plasma spray process. It is found that improvements can be made by annealing the ferrite films at 500 degreesC-800 degreesC. The annealing induced magnetic property changes are studied by neutron diffraction and ferromagnetic resonance techniques. The increase of the saturation magnetization is attributed to the cation ordering within the spinel lattice, which increases the magnetic moment per ferrite formula. The refinements on the neutron diffraction data suggest that the redistribution of the cation during annealing neither starts from a fully disordered state nor ends to a fully ordered state. The decrease of the coercivity is analyzed with the domain wall pinning model. The measurements on the magnetostriction and residual stress indicate that coercive mechanisms arising from the magnetoelastic energy term are not dominant in these ferrite films. The decrease of the coercivity for annealed ferrite films is mainly attributed to the decrease of the effective anisotropic field, which may result from the homogenization of the film composition and the reduction of the microstructural discontinuity (e.g., cracks, voids, and splat boundaries). (C) 2005 American Institute of Physics.

Abstract: Plasma-sprayed MnZn ferrite thick films are built up by splats, which consist of columnar grains with diameter similar to200 nm and height similar to1 pmu. The existence of the conductive wustite FeO in the as-sprayed films greatly reduces the dc resistivity. However, a useful structure can be developed in these ferrite films with fine equal-axis ferrite grains insulated by the high-resistivity hematite Fe2O3 because of the polygonization of the columnar grains and the oxidation of the wustite during an annealing process. The dc resistivity increases significantly after the annealing process, an effect ascribed to the growth of hematite Fe2O3 on the basis of impedance analysis. The magnetic properties of these ferrite films improve concurrently. The high-frequency response of the annealed plasma-sprayed MnZn ferrites shows a permeability of similar to700 stabilized to above 10 MHz. The maximum Q factor at about 10 MHz increases from 5 to 20 as a result of the increase of the dc resistivity.

Abstract: The antiferromagnetic phase FeO (wustite) forms in plasma-sprayed MnZn ferrites from pure spinel phase powder. An exchange bias is observed in hysteresis loops of both ferrite coatings and single splats; the exchange bias decreases and disappears with annealing. X-ray diffraction indicates that the wustite FeO changes to hematite Fe2O3 upon annealing. Annealing-induced cation ordering and diffusion influence the ferrite magnetic properties by increasing the saturation magnetization and decreasing the coercivity.

Abstract: Energy dispersive X-ray analysis performed on plasma-sprayed MnZn ferrite (MZF) single �splats� shows a variation in zinc content within splats of different sizes after the spray process, even though the powder has the same starting stoichiometry. A simple model indicates that smaller particles have a higher zinc evaporation rate during the in-flight time. However, the significant decrease of zinc in smaller ferrite particles is mainly attributed to their large surface-to-volume ratio. Compositional differences due to a random cation distribution condition results in magnetic property variations among MZF splats. The coating inhomogeneity due to zinc loss increases the coercivity of the plasma-sprayed MnZn ferrites. The magnetic properties of the MnZn ferrites can be improved through long-range (diffusion) and short-range (ordering) cation redistribution upon low temperature annealing. (C) 2004 Acta Materialia, Inc. Published by Elsevier Ltd. All rights reserved.

Abstract: MnZn ferrite coatings fabricated by plasma spray have the advantage of a columnar structure with average grain size between 200-300 nm, somewhat analogous to that of conventional laminated cores used to minimize the eddy current loss at high frequency. The resistivity of these ferrite coatings increases by four orders of magnitude after a simple annealing process at 500 degreesC in air. Our studies reveal that this change is due to oxygen diffusion through the grain boundaries, which results in the oxidation of Fe2+ to Fe3+ and inhibits the �hopping� conductivity effect between Fe2+ and Fe3+. The initial permeability at 100 kHz increases from around 500 to above 1000. This change is believed to be due to the local- and long-range redistribution of Mn and Zn, which improves the soft magnetic properties of the ferrite coatings.

Abstract: A simple synthesis protocol for PbTe nanowires (NWs) preparation with controlled size, e.g. diameter 10 similar to 30 nm and length 500 similar to 3000 nm, and enhanced seebeck coefficient was demonstrated. The ID growth of PbTe NWs was directed due to the surface bonds between Pb and sucrose, which formed the soft stacking template due to the pi-pi electron interaction. The size and morphology of the NWs were controlled with respect to the reaction temperatures and heating rates, e.g. by injecting the precursors to the solvent directly at 180 degrees C or by heating the precursors gradually from room temperature to 180 degrees C. Very high p-type seebeck coefficients >470 mu V/K at T = 375 similar to 425 K were obtained in the film samples made from PbTe NWs after hydrazine washing and annealing at 300 degrees C in vacuum. The high seebeck coefficient value was suspected to be related to quantum size confinement or due to phonon drag scattering of the charge carriers. These NWs may give promising potentials for architecture of thermoelectric module applications.