Yonhua Tzeng

National Cheng Kung University, 臺南市, Taiwan, Taiwan

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Publications (60)143.45 Total impact

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    ABSTRACT: Science and technology are presented for novel nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) encapsulated NG/copper anode and UNCD coatings that may enable next generation Li-ion batteries (LIBs) with potential 10x longer lifetime and superior performance than current LIBs. N-UNCD films (∼5-10 nm grain size) exhibit electrical conductivity and extreme resistance to chemical corrosion, providing superior performance with respect to current uncoated anodes.
    Advanced Materials 03/2014; · 14.83 Impact Factor
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    ABSTRACT: Nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) and multi-layer-graphene-like hybrid carbon films have been synthesized by microwave plasma enhanced chemical vapor deposition (MPECVD) on oxidized silicon which is pre-seeded with diamond nanoparticles. MPECVD of N-UNCD on nanodiamond seeds produces a base layer, from which carbon structures nucleate and grow perpendicularly to form standing carbon platelets. High-resolution transmission electron microscopy and Raman scattering measurements reveal that these carbon platelets are comprised of ultrananocrystalline diamond embedded in multilayer-graphene-like carbon structures. The hybrid carbon films are of low electrical resistivity. UNCD grains in the N-UNCD base layer and the hybrid carbon platelets serve as high-density diamond nuclei for the deposition of an electrically insulating UNCD film on it. Biocompatible carbon-based heaters made of low-resistivity hybrid carbon heaters encapsulated by insulating UNCD for possible electrosurgical applications have been demonstrated.
    Scientific Reports 01/2014; 4:4531. · 5.08 Impact Factor
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    ABSTRACT: Effects of biasing voltage-current relationship on microwave plasma enhanced chemical vapor deposition of ultrananocrystalline diamond (UNCD) films on (100) silicon in hydrogen diluted methane by bias-enhanced nucleation and bias-enhanced growth processes are reported. Three biasing methods are applied to study their effects on nucleation, growth, and microstructures of deposited UNCD films. Method A employs 320 mA constant biasing current and a negative biasing voltage decreasing from -490 V to -375 V for silicon substrates pre-heated to 800 °C. Method B employs 400 mA constant biasing current and a decreasing negative biasing voltage from -375 V to -390 V for silicon pre-heated to 900 °C. Method C employs -350 V constant biasing voltage and an increasing biasing current up to 400 mA for silicon pre-heated to 800 °C. UNCD nanopillars, merged clusters, and dense films with smooth surface morphology are deposited by the biasing methods A, B, and C, respectively. Effects of ion energy and flux controlled by the biasing voltage and current, respectively, on nucleation, growth, microstructures, surface morphologies, and UNCD contents are confirmed by scanning electron microscopy, high-resolution transmission-electron-microscopy, and UV Raman scattering.
    12/2013; 115(2).
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    ABSTRACT: We report on a polarized Raman study on mechanically cleaved single-layer graphene films. Under a specific orientation of scattering measurement, the width and position of the G peak change with the incident polarization direction, while the integrated intensity of that is unaltered. This phenomenon is explained by a proposed mode in which the peak is contributed by a mixture of un-, compressive-, and tensile-strained G sub-modes. The compression and tension are both uniaxial and approximately perpendicular to each other. They are undesigned and located in either separated or overlapped sub-areas within the probed local region. Compared to the unstrained wavenumber of 1580 cm(-1), compression induces a blue shift while tension causes a red one. The sub-modes correlated with the light polarization through different relationships split the G peak into three sub-ones. We develop a method to quantitatively analyze the positions, widths, intensities, and polarization dependences of sub-peaks. This analysis quantitatively reveals local strain, which changes with the detected area of a graphene film. The method presented here can be extended to detect the strain distribution in the film and thus is a promising technology for graphene characterization.
    Nanoscale 07/2013; · 6.73 Impact Factor
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    ABSTRACT: Fluorescence quenching effects on graphene or hydrogen-terminated graphene covered sliver nanoparticles are studied and the results are explained with energy transfer models. The fluorescence signal of R6G is suppressed by the graphene flakes via Förster resonance energy transfer and by the silver nanoparticles via surface energy transfer. The relative fluorescence intensities of R6G are reduced to 28% and 69% on the single-atom-thick graphene flake and the hydrogen-terminated graphene covered silver film, respectively. The mechanism of the quenching effect is illustrated by the energy diagram of electron transition.
    Applied Physics Letters 02/2013; 102(5). · 3.79 Impact Factor
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    ABSTRACT: Various chromium-containing amorphous hydrogenated carbon (a-C:H/Cr) coatings were deposited on oxygen-free copper and silicon substrates for use as solar selective absorber coatings. The deposition was performed using a magnetron co-sputter deposition method under various methane/Ar ratios, ranging from 0 to 8%. The obtained films were characterized using glazing incident X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, secondary ion mass spectrometer, and X-ray photoelectron spectroscopy. The optical absorptance and emittance at 100 °C were determined using UV–vis-NIR spectroscopy and Fourier transform infrared spectrometry, respectively. Effects of the material characteristics on the optical properties are reported and discussed.
    Thin Solid Films 02/2013; 529:164–168. · 1.87 Impact Factor
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    ABSTRACT: C K-, Cr L3.2-, and K-edge X-ray absorption near-edge structure (XANES) analysis, high-resolution transmission electron microscopy examination, and optical absorptance have been examined to obtain a correlation between the optical absorptance and electronic structure of chromium-containing amorphous hydrogenated carbon thin films (a-C:H/Cr) deposited using a dc magnetron sputter deposition technique. It was found that the C 2pCr 3d hybridization gradually increases as the Cr nanoparticle (NP) size decreases, accompanied by a C 2p interband transition. The amount of CH bonding and the change in crystalline structure are the main factors affecting the optical absorptance of the thin films. The size of the Cr NP affects the absorption wavelength range of the films. The optical absorptance and C K-edge XANES spectra indicate that a decrease in the size of Cr NP raises the conduction-band-minimum and may also increase the bandgap.
    Applied Surface Science 01/2013; 264:202–206. · 2.54 Impact Factor
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    ABSTRACT: Bias-enhanced nucleation and growth of ultrananocrystalline diamond (UNCD) nano-pillars on silicon substrates by low-pressure microwave plasma chemical vapor deposition in a hydrogen-rich gas mixture with methane is reported. Direct-current biasing of the substrate in a constant-current mode is applied to substrates, which are pre-heated to 800 °C, to result in a negative bias voltage of greater than 350 V throughout the nucleation and growth process. Self-masking by UNCD clusters, angle dependent sputtering of UNCD clusters, and ion-assisted chemical vapor deposition by bias enhanced bombardment of energetic ions are attributed to the formation of UNCD nano-pillars. High-resolution transmission electron microscopy analysis indicates that an interfacial layer exists between the silicon substrate and the UNCD nano-pillars. The porous UNCD film with high-density nano-pillars exhibits excellent optical anti-reflectivity and improved electron field emission characteristics compared to smooth and solid UNCD films.
    Journal of Applied Physics 12/2012; 112(12). · 2.21 Impact Factor
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    ABSTRACT: Effects and mechanisms of conductivity variation of chemically vapor deposited single-layer graphene covering silver nanoparticles on SiO<sub>2</sub>/Si are reported based on blue-light (405nm) induced plasmonic coupling and electrical current induced annealing and desorption of surface adsorbates. With 1V applied voltage, photoconductivity is positive except a brief negative period when the graphene is first illuminated by light. At 10mV applied voltage, negative photoconductivity persists for hours. In comparison, negative photoconductivity of graphene on pristine SiO<sub>2</sub>/Si persists for tens of hours. When the applied voltage is increased to 1V, it takes tens of hours of light illumination to change to positive photoconductivity.
    Optics Express 09/2012; 20(20):22943-52. · 3.55 Impact Factor
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    ABSTRACT: We report on effects of a tungsten layer deposited on silicon surface on the effectiveness for diamond nanoparticles to be seeded for the deposition of ultrananocrystalline diamond (UNCD). Rough tungsten surface and electrostatic forces between nanodiamond seeds and the tungsten surface layer help to improve the adhesion of nanodiamond seeds on the tungsten surface. The seeding density on tungsten coated silicon thus increases. Tungsten carbide is formed by reactions of the tungsten layer with carbon containing plasma species. It provides favorable (001) crystal planes for the nucleation of (111) crystal planes by Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD) in argon diluted methane plasma and further improves the density of diamond seeds/nuclei. UNCD films grown at different gas pressures on tungsten coated silicon which is pre-seeded by nanodiamond along with heteroepitaxially nucleated diamond nuclei were characterized by Raman scattering, field emission-scanning electron microscopy, and high resolution-transmission electron microscopy.
    Journal of Applied Physics 06/2012; 111(12). · 2.21 Impact Factor
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    ABSTRACT: Effects of plasmonic coupling on blue laser induced positive and negative photoconductivity of chemically vapor deposited mono-layer graphene transferred onto SiO2/Si with or without silver nanoparticles in ambient atmosphere are reported. Ggraphene on silver nanoparticles coated SiO2/Si exhibits negative and rapidly decreasing photoconductivity upon light illumination. The photoconductivity recovers gradually and then become positive photoconductivity. In the subsequent on-off cycles of light illumination, the graphene exhibits positive photoconductivity. Graphene on SiO2/Si without silver nanoparticles also exhibits negative and rapidly decreasing photoconductivity upon light illumination followed by a gradual increase in conductivity. However, the negative photoconductivity persists for a test period longer than 30 hours when light is turned on and off. Adverse effects on electrical conductivity due to electron scattering by surface and interfacial charges, decrease in surface dopants due to desorption induced by incident photons, plasmonic coupling induced local electromagnetic fields combined with enhanced electron transport between silver nanoparticles, and photon generated electron-hole pairs in silicon contribute to the measured photoconductivity. Annealing by electrical current and Joule heating adds to the complexity of the observed effects of current density on positive and negative persistent photoconductivity.
    Nanotechnology (IEEE-NANO), 2012 12th IEEE Conference on; 01/2012
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    ABSTRACT: Synthesis of graphene of large domain sizes in order to minimize scattering of charge carriers in grain boundaries is an essential process to be achieved before the full merits of graphene can be realized for next-generation nanoelectronics. Independent control of nucleation processes and growth processes in the complicated chemical vapor deposition environments is a key to achieving this goal. Catalyst assisted chemical vapor deposition of graphene on copper at around 1000°C near the melting point of copper in hydrogen diluted methane is fine tuned to reach dynamic balance between etching and growth of graphene. Surface diffusion of carbon atoms generated from methane and other hydrocarbon species, including those from etching graphene by atomic hydrogen, generated by the assistance of copper catalyst on the surface of copper foil results in complicated network of graphene domains separated by alley-like gaps of nearly equal width. By controlling the dynamic balance point, independent control of nucleation and growth and the synthesis of large individual graphene of various unique shapes and graphene films with networked alleys have been demonstrated.
    Nanotechnology (IEEE-NANO), 2012 12th IEEE Conference on; 01/2012
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    Ji-heng Jiang, Yonhua Tzeng
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    ABSTRACT: We report on mechanisms for suppressing diamond secondary nucleation in microwave plasma self-bias-enhanced growth (SBEG) of diamond films in methane diluted by argon. High-density plasma at a small distance from the substrate induces a floating potential which promotes high-flux, low-energy ion bombardment on diamond growing surfaces along with an equal flux of electrons. Increased atomic hydrogen generated by electron impact dissociation of methane and low-energy ion bombardment help remove hydrocarbon coatings on diamond grains in favor of continuous grain growth and, therefore, the suppression of secondary diamond nucleation. Energetic meta-stable excited argon, abundant C2 dimers, and enhanced effective surface temperature due to low-energy ion bombardment further promote the diamond grain growth resulting in the deposition of a diamond film with columnar diamond grains of much larger grain sizes and a much lower density of grain boundaries than ultrananocrystalline diamond (UNCD) films grown under similar conditions without optimized plasma-substrate interactions. SEM, XRD, PL, and Raman scattering help confirm the deposition of diamond films with columnar grains.
    AIP Advances 10/2011; 1(4). · 1.35 Impact Factor
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    ABSTRACT: We report on strong plasmonic coupling from silver nanoparticles covered by hydrogen-terminated chemically vapor deposited single-layer graphene, and its effects on the detection and identification of adenine molecules through surface-enhanced Raman spectroscopy (SERS). The high resistivity of the graphene after subjecting to remote plasma hydrogenation allows plasmonic coupling induced strong local electromagnetic fields among the silver nanoparticles to penetrate the graphene, and thus enhances the SERS efficiency of adenine molecules adsorbed on the film. The graphene layer protects the nanoparticles from reactive and harsh environments and provides a chemically inert and biocompatible carbon surface for SERS applications.
    Optics Express 08/2011; 19(18):17092-8. · 3.55 Impact Factor
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    ABSTRACT: A novel SERS sensor for adenine molecules is fabricated electrochemically using an ordered two-dimensional array of self-aligned silver nanoparticles encapsulated by alumina. Silver is electro-deposited on the interior surfaces at the bottom of nano-channels in a porous anodic aluminum oxide (AAO) film. After etching aluminum, the back-end alumina serves as a SERS substrate. SERS enhancement factor greater than 10(6) is measured by 532 nm illumination. It exhibits robust chemical stability and emits reproducible Raman signals from repetitive uses for eight weeks. The inexpensive mass production process makes this reliable, durable and sensitive plasmon based optical device promising for many applications.
    Optics Express 06/2011; 19(12):11441-50. · 3.55 Impact Factor
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    ABSTRACT: RF MEMS capacitive switches using leaky nanodiamond as a dielectric film are studied and compared with those using Si3N4. Characteristics of dielectric charging and discharging are analyzed at temperature ranging from −196°C to 150°C. Electrical resistivity of leaky nanodiamond is measured to be lower than that of Si3N4 by 3 to 6 orders of magnitude at room temperature. Trapped charges in leaky nanodiamond dielectric discharge much more quickly than those in Si3N4 while the power dissipation of nanodiamond based switches remains low. As a result, charge trapping induced shift in electrostatic actuation voltage is greatly reduced compared to that with Si3N4 and becomes non-detectable under the reported conditions. RF MEMS capacitive switches based on leaky nanodiamond dielectric are, therefore, more reliable than those with Si3N4.
    Diamond and Related Materials 01/2011; 20(4):546-550. · 1.71 Impact Factor
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    ABSTRACT: The dielectric porous anodic aluminum oxide films with embedded silver nanoparticles arrays have photoinduced plasmon-coupling and can be applied to photo-absorption sensors. We systematically change the pore diameter and inter-pore spacing to investigate their influence.
    Quantum Electronics Conference & Lasers and Electro-Optics (CLEO/IQEC/PACIFIC RIM), 2011; 01/2011
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    ABSTRACT: Ordered 2-D arrays of silver nanoparticles encapsulated by anodic alumina have been fabricated electrochemically to demonstrate reliable, durable, reproducible, and high sensitivity sensing by means of surface-enhanced Raman spectroscopy of micro- and nano-materials including inorganic and organic molecules. In this paper, fabrication process of the sensor and its applications to detection and identification of R6G and adenine molecules and the measurement of the molecular concentration will be presented. This novel sensor combines the excellent intrinsic performance of silver plasmon resonance and the effective isolation of silver from harsh environments by alumina encapsulation to achieve high performance and long-term reliability.
    01/2011;
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    ABSTRACT: A novel low-stress process for transferring thermal CVD single-layer graphene from copper foils to destination substrates is demonstrated. Electrical and optical characteristics of as-transferred graphene and the hydrogen remote-plasma modified graphene are presented. Although graphene is mechanically very strong considering its atomically thin structure, large-area single-layer graphene is practically very fragile especially during handling and transfer from one substrate to another. Handling of large-area free-standing graphene is even more challenging. Combination of effective transfer and surface treatment of graphene by hydrogenation allows fine tuning of its electrical resistivity for practical applications.
    01/2011;
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    ABSTRACT: This paper reports on room-temperature high-density diamond seeding for low-temperature microwave plasma enhanced chemical vapor deposition of nanocrystalline diamond (NCD) on W/Si substrates. A tungsten layer acts as a diamond nucleation-enhancing layer. Formation of tungsten-carbide (WC) complex increases the initial nucleation density and plays an important role in facilitating diamond growth characteristics. Microwave plasma-enhanced chemical vapor deposition is applied to synthesize diamond films in Ar diluted by methane without hydrogen additives at low temperature. NCD seeding and film formation were investigated as a function of the thickness of tungsten interfacial layer. Raman spectroscopy, SEM, AFM and TEM were applied to characterize NCD films in order to gain insight into the initial stage of NCD diamond synthesis.
    01/2011;