Chaoying Ni

University of Delaware, Delaware, United States

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Publications (59)149.9 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Nickel based materials have been intensively investigated and considered as good potential electrode materials for pseudocapacitors due to their high theoretical specific capacity values, high chemical and thermal stability, ready availability, environmentally benign nature and lower cost. This review firstly examines recent progress in nickel oxides or nickel hydroxides for high performance pseudocapacitor electrodes. The advances of hybrid electrodes are then assessed to include hybrid systems of nickel based materials with compounds such as carbonaceous materials, metal and transition metal oxides or hydroxides, in which various strategies have been adopted to improve the electrical conductivity of nickel oxides or hydroxides. Furthermore, the energy density and power density of some recently reported NiO, nickel based composites and NiCo2O4 are summarized and discussed. Finally, we provide some perspectives as to the future directions of this intriguing field.
    Journal of Power Sources 12/2014; 267:430–444. · 5.26 Impact Factor
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    ABSTRACT: Halloysite nanotube supported hybrid CeO2–AgBr nanocomposite was synthesized by a facile microwave mediated method. The molar ratio of CeO2 and AgBr in the halloysite–CeO2–AgBr nanocomposite was adjusted so that r = nAg/(nAg + nCe) was selected as 0.0, 0.25, 0.33, 0.40, 0.45, and 0.50 respectively. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Visible diffused reflectance spectroscopy (UV–Vis) were employed to investigate the structure and optical properties of the nanocomposites. Results indicate that among the pure halloysite and CeO2–AgBr loaded halloysite nanocomposites, the molar fraction r has a critical effect on the photocatalytic activity, which increases as the AgBr content increases to r ≤ 0.4 and decreases when r > 0.4. The highest conversion of methyl orange reached 99% within 80 min by using halloysite–CeO2–AgBr at r = 0.4, which was much higher than pure halloysite and CeO2–AgBr. As an exploratory study, the introduction of AgBr species was found to extend the spectral response from UV to visible region and improve the separation of electron–hole pairs. The repeatable use of the nanocomposite photocatalyst with little depreciation was also confirmed.
    Applied Clay Science 11/2014; · 2.34 Impact Factor
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    ABSTRACT: Novel ZnO core/shell nanostructures were constructed by depositing a porous ZnO layer directly on the surfaces of pre-fabricated ZnO nanowires through a facile chemical method. The morphology and structure of the obtained products have been investigated by field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction analysis. In these unique nanostructures, the porous overlayer exhibits a large surface area for sufficient dye loading to enhance light harvesting and the ZnO nanowire cores provide direct conduction pathways for the photogenerated electron transport to diminish the chance of electron recombination. The obtained ZnO nanostructures were used as photoanode material in dye-sensitized solar cell which showed an increase in performance of 141 % compared with an equivalent solar cell employing ZnO nanowire arrays as photoanode. This result was achieved mainly due to an increase in photogenerated current density directly resulting from improved light harvesting of the porous layer.
    Journal of Materials Science Materials in Electronics 10/2014; 25(10). · 1.49 Impact Factor
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    ABSTRACT: Graphical abstract A novel hierarchical nanostructure consisting of a zinc hydroxide fluoride nanorod core with a shell of porous wrinkle textured zinc carbonate hydroxide was fabricated. The obtained precursors were transformed by calcination to porous ZnO nanostructures with the original morphologies and pore structures retained. The yielded ZnO shows superior photoelectric conversion performance in solar cell application.
    Journal of Alloys and Compounds 09/2014; 607:132–138. · 2.73 Impact Factor
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    ABSTRACT: Nanoscale blending of electron-donor and electron-acceptor materials in solution-processed bulk heterojunction (BHJ) organic photovoltaic (OPV) devices is crucial for achieving high power conversion efficiency (PCE). We used a classic blend of P3HT:PCBM as a model to observe the nanoscale morphology of the P3HT fibrils and PCBM nanoclusters in the mixture. Energy-filtered transmission electron microscopy (EFTEM) clearly revealed a nanoscopic phase separation. Randomly connected and/or non-connected P3HT fibrous networks and PCBM domains, revealed by 2-dimensional (2D) micrographs, were observed by collecting electron energy loss spectra in the range of 19 eV and 30 eV. From EFTEM images, the average length and the diameter of P3HT fibrils were found to be approximately 70±5 nm and 15±2 nm, respectively. Combining the EFTEM, selected area electron diffraction (SAED) and X-ray diffraction (XRD) results, we were able to determine the number and spacing of the ordered chains in P3HT fibrils. There were 18+3 repeating units of P3HT perpendicular to the fibril, ∽184 layers of pi-pi stacking along the fibril and ∼9 layers of interchain stacking within the fibril. These conclusive observations provide an insight into the number of molecules found in one instance of ordered-plane stacking. This information is useful for the calculation of charge transport in semicrystalline polymers. Using crosssection samples prepared with a focused ion beam (FIB) technique, the vertical morphology of each phase was analyzed. By collecting 30 eV energy loss images, the phase separation in P3HT:PCBM system was distinguishable. A higher P3HT concentration was observed at the top of the cell, near Al contact, which could possibly cause loss of carriers and recombination due to a mismatch in the P3HT and Al energy bands.
    ACS Applied Materials & Interfaces 07/2014; · 5.90 Impact Factor
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    ABSTRACT: Attapulgite/polypyrrole composites (ATP/PPys) with morphology difference were synthesized in water–ethanol mixture via modulating the surface property of ATP to expound the relationship of morphology and electrica property. The surface property of ATP shows important impacts on the modulated morphology of ATP/PPys, and their morphologies are closely related with the inherent property. The results indicate that the pristine ATP is beneficial to generate the rod-film composites, and the rod-film ATP/PPys have preferable electrical conductivity and specific capacitance compared with the rod–sphere ones.
    Materials Letters 07/2014; 126:135–138. · 2.27 Impact Factor
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    ABSTRACT: The FePt alloy in the high magnetic anisotropy L10 phase is one of the most promising magnetic materials in many applications, including ultra-high-density magnetorecording. A new green chemical approach to synthesize magnetically hard L10 FePt nanoparticles is described in this paper by using crystalline saline complex hexaaquairon(II)hexachloroplatinate, [Fe(H2O)6]PtCl6, as the precursor. The crystal structure of this complex shows alternate layers of Fe and Pt atoms. After ball milling, annealing at 400 °C under a reducing atmosphere leads to the direct formation of FePt nanoparticles in the highly ordered L10 phase. This method is a green synthesis due to the low temperature for phase transformation, and the absence of organic solvents or surfactants in the reaction. Indeed the milling step is performed using NaCl as media, which can be easily removed with water. By varying the precursor/NaCl ratio, particles with size in the range of 6.2–13.2 nm were obtained. With the decrease of particle size, the room temperature coercivity of FePt nanoparticles also decreased from 10.9 kOe to 4.7 kOe.
    Green Chemistry 03/2014; 16(4). · 6.83 Impact Factor
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    ABSTRACT: Chalcogenide glasses, namely the amorphous compounds containing sulfur, selenium, and/or tellurium, have emerged as a promising material candidate for mid-infrared integrated photonics given their wide optical transparency window, high linear and nonlinear indices, as well as their capacity for monolithic integration on a wide array of substrates. Exploiting these unique features of the material, we demonstrated high-index-contrast, waveguide-coupled As2Se3 chalcogenide glass resonators monolithically integrated on silicon with a high intrinsic quality factor of 2 × 105 at 5.2 micron wavelength, and what we believe to be the first waveguide photonic crystal cavity operating in the mid-infrared.
    02/2014;
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    ABSTRACT: Thin film processing methods offer a number of means to investigate and engineer ion conduction in solid electrolytes. In this work, we present fabrication and characterization of Y-doped CeO2 thin films where the Y-dopants were distributed homogeneously or were condensed into increasingly concentrated layers, to the limit of alternating layers of pure Y2O3 and pure CeO2. Both the entire film thickness and net Y-concentration were kept constant such that only the spatial distribution of dopants was altered. Space charge regions formed at interfaces between regions with varying vacancy concentrations, yielding vacancies trapped within two-dimensionally arranged accumulation regions. A Gouy–Chapman model was implemented in order to further investigate the distribution of the accumulated oxygen vacancies in the space charge regions of pure CeO2 layers. Comparison of the measured activation energy of conduction indicates that in films with intermediate dopant condensation, conduction occurred predominantly by vacancies trapped in the Y-containing layers. Conversely, in the film composed of alternating layers of Y2O3 and CeO2, vacancies trapped in the CeO2 space charge regions became significantly conductive, thus providing a means to determine the properties of vacancies in ceria that are trapped near dopants.
    Solid State Ionics 02/2014; 255:13–20. · 2.05 Impact Factor
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    ABSTRACT: In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiNx waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.
    Science and Technology of Advanced Materials 01/2014; 15(1):014603. · 3.75 Impact Factor
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    ABSTRACT: Spin-orbit interaction-driven phenomena such as the spin Hall and Rashba effect in ferromagnetic/heavy metal bilayers enables efficient manipulation of the magnetization via electric current. However, the underlying mechanism for the spin-orbit interaction-driven phenomena remains unsettled. Here we develop a sensitive spin-orbit torque magnetometer based on the magneto-optic Kerr effect that measures the spin-orbit torque vectors for cobalt iron boron/platinum bilayers over a wide thickness range. We observe that the Slonczewski-like torque inversely scales with the ferromagnet thickness, and the field-like torque has a threshold effect that appears only when the ferromagnetic layer is thinner than 1 nm. Through a thickness-dependence study with an additional copper insertion layer at the interface, we conclude that the dominant mechanism for the spin-orbit interaction-driven phenomena in this system is the spin Hall effect. However, there is also a distinct interface contribution, which may be because of the Rashba effect.
    Nature Communications 01/2014; 5:3042. · 10.74 Impact Factor
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    ABSTRACT: We have demonstrated what we believe to be the first waveguide photonic crystal cavity operating in the mid-infrared. The devices were fabricated from Ge<sub>23</sub>Sb<sub>7</sub>S<sub>70</sub> chalcogenide glass (ChG) on CaF<sub>2</sub> substrates by combing photolithographic patterning and focused ion beam milling. The waveguide-coupled cavities were characterized using a fiber end fire coupling method at 5.2 μm wavelength, and a loaded quality factor of ∼2000 was measured near the critical coupling regime.
    Optics Letters 08/2013; 38(15):2779-82. · 3.39 Impact Factor
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    ABSTRACT: In this work we report fabrication and microstructural characterization of single crystalline Sm2Co17 nanoparticles with an average size of 103.7 nm. These particles are fabricated using mechanochemical method and can be used for fabrication of high performance permanent magnets due to their high coercivity (20 kOe). Microstructure analysis reveals the inhomogeneity and defects in the nanoparticles. The origin of these defects was analyzed and discussed by systematic microstructural investigation of the as-milled, annealed, and washed samples. On the basis of these results, by further optimizing the processing parameters, properties of the nanoparticles can be improved.
    The Journal of Physical Chemistry C 05/2013; 117(20):10291–10295. · 4.84 Impact Factor
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    ABSTRACT: Yttria-stabilized zirconia (YSZ) thin films with thickness ranging from 6 nm to 100 nm were prepared by RF sputtering on (0001) Al2O3 substrates and exhibited epitaxial growth along (111)[110] YSZ//(0001)[100] Al2O3. While the thicker films exhibited oxygen ion conductivities similar to bulk samples, the thinnest films exhibited increased ionic conductivity and a reduced activation energy of 0.79 eV between 300 °C–650 °C. Concomitant with the improved conductivity of the thinner films is an increase in the out-of-plane lattice parameter, matching theoretical expectations regarding tensile strain, and the introduction of edge dislocations, which may additionally assist in-plane ionic conduction.
    Applied Physics Letters 04/2013; 102(14). · 3.52 Impact Factor
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    ABSTRACT: We experimentally demonstrated for the first time on-chip cavity-enhanced mid-infrared spectroscopic sensing of chemical molecules, performed near 5.2 μm wavelength using Ge23Sb7S70 resonators monolithically fabricated on CaF2 substrates.
    Sensors, 2013 IEEE; 01/2013
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    ABSTRACT: Anisotropic SmCo5 nanoflakes prepared by high-energy ball-milling with surfactants have great potential in applications for high-performance nanocomposite magnets. For such “nanocomposite” applications, the surface structure and chemistry of nanoflakes are crucial for achieving high coercivity. In this study, hot-pressed samples from anisotropic SmCo5 nanoflakes, ball-milled with different surfactants, oleic acid (OA) and oleylamine (OY), were investigated. Interface layers between the SmCo5 nanoflakes were found to consist of samarium oxides and a soft magnetic Co phase. These surface layers contribute to the degradation of hard magnetic performance, which is confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy analysis of the cross-section of a single flake ball-milled with OA. Samples milled with OY show a much thinner interface layer in compacted samples, which means that the surface degradation during ball-milling with OY is much less than that with OA. The results show clearly that the choice of proper surfactant and the control of processing parameters are the key factors for improving the surface condition of the nanoflakes and the resulting hard magnetic properties.
    Acta Materialia. 11/2012; 60(19):6685–6691.
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    ABSTRACT: By controlling the interaction between cationic surfactant micelles and ammonium metatungstate during the formation of mesoporous silica structure, highly dispersed tungsten carbide (WC) nanoparticles of 2.0 nm in diameter on mesoporous silica nanospheres were synthesized at lower concentration of ammonium metatungstate. With additional ammonium metatungstate, a novel mesoporous silica nanobamboo structure was formed with bimodal size-distributed WC nanoparticles, in which 2.0 nm WC was homogeneously distributed in nanobamboo's mesoporous silica wall and those with larger diameter (10.0-20.0 nm) were only formed on the nanobamboo's inner surface and at its internodes. The mesoporous silica nanobamboo also had a very high tensile strength due to its bamboo-like structure.
    Dalton Transactions 04/2012; 41(23):6914-8. · 4.10 Impact Factor
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    ABSTRACT: The effect of Mo and MoS2 additions on the magnetic and microstructure properties has been investigated in Nd–Fe–Ga–B sintered magnets. Coercivity can be increased by both the additions, but the MoS2 addition provides the larger increase per Mo atom for up to 0.6 at.% Mo. Microstructure investigation reveals a new amorphous intergranular Ga rich phase. This phase forms a thin layer in the grain boundaries and leads to a wetting behavior of the grain boundary phase, therefore increasing the coercivity. Molybdenum addition in the form of MoS2 is found to modify the Nd2Fe14B phase, rather than form new minority phases, and the coercivity enhancement of the magnet is due to the increased anisotropy field of the hard magnetic phase.
    Journal of Magnetism and Magnetic Materials 04/2012; 324(7):1391–1396. · 2.00 Impact Factor
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    ABSTRACT: We present results on the comparative studies of the surfaces of oxygen passivated FeCo nanoparticles (NPs) and thin films prepared by inert gas condensation and pulse laser deposition, respectively. Morphology and structure of the NPs and thin films are investigated by transmission electron microscopy (TEM) and X-ray diffraction. Due to the larger surface area, thicker oxide over-layer is observed for particles in comparison with thin films. X-ray photoelectron spectroscopy (XPS) spectra strongly depended on the morphology and oxide over layer thicknesses for nanostructures. This leads to observation of clearly different background and is explained in term of different cationic distribution in the overlayer, thicknesses, and morphology (enhanced surface area) of the nanostructures. TEM analyses showed an oxide over-layer on the NP of approximately 2.6 nm, which is consistent with the theoretical model based on electron attenuation lengths. However, in the case of thin films a much thinner oxide over-layer of about 1.3 nm was observed. As expected, XPS spectra of oxygen passivated particles show oxide peaks with weak metal peaks compared to oxygen passivated thin films which show significantly high zero-valent metal peaks.
    physica status solidi (a) 01/2012; · 1.21 Impact Factor
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    ABSTRACT: We studied the real-time evolution of magnetic dynamic and static properties of 20 nm CoFeB thin film during annealing at 380 °C. The ferromagnetic resonance linewidth quickly reduces by 30% within 300 s annealing, and monotonically increases upon longer annealing. The magnetic static coercivity shows similar trend. The underlying physical relation between linewidth and anisotropy can be connected by the two-magnon scattering theory. By doping of Nb into CoFeB films, the damping was maintained at a low value within 2000 s annealing. This method to tailor the dynamic properties of CoFeB may benefit the development of magnetics and spintronics based microwave devices.
    Applied Physics Letters 01/2011; 98(4):042506-042506-3. · 3.52 Impact Factor

Publication Stats

341 Citations
149.90 Total Impact Points

Institutions

  • 2002–2014
    • University of Delaware
      • • Department of Materials Science and Engineering
      • • Department of Physics and Astronomy
      Delaware, United States
    • Chosun University
      • Department of Environmental Engineering
      Kwangju, Gwangju, South Korea
  • 2008
    • University of Engineering and Technology, Lahore
      • Department of Metallurgical and Materials Engineering
      Lahore, Punjab, Pakistan
  • 2007
    • Universität Bremen
      Bremen, Bremen, Germany