Nosang V. Myung

University of California, Riverside, Riverside, California, United States

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Publications (181)530.36 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Three-dimensional hybrid nanostructures (i.e., Te "nanobranches" on a Si "nanotrunk" or Te "nanoleaves" on a Si "nanotrunk") were synthesized by combining the gold-assisted chemical etching of Si to form Si "nanotrunks" and the galvanic displacement of Si to form Te "nanobranches" or "nanoleaves." By adjusting the composition of the electrolyte used for the galvanic displacement reaction, the shape of the Te nanostructures could be changed from nanoleaves to nanobranches. The Si nanotrunks with Te nanobranches showed stronger luminescent emission in the visible region, with their Raman spectrum having a higher wave number, owing to their grain size being larger. This suggested that the optical and photoelectrochemical properties of Te-Si hybrid nanostructures depend on their shape and size. Using this approach, it should be possible to fabricate various hierarchical nanostructures for use in photoelectronic and photoelectrochemical devices.
    Nanoscale 07/2014; · 6.23 Impact Factor
  • NSTI Nanotech; 06/2014
  • NSTI Nanotech; 06/2014
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    ABSTRACT: Camphor-10-sulfonic acid (HCSA) doped polyaniline (PANI)/poly(ethylene oxide) (PEO) composite nanofibers with different compositions (12 to 52 wt.% of PANI) were synthesized by an electrospinning method and their properties including optical, electrical and sensing were systematically investigated. FT-IR shows that an increase of IR absorbance ratios of aromatic CC stretching vibration of benzenoid rings of PANI to COC symmetric vibrational modes of PEO confirmed that the PANI content in nanofiber mats increased proportionally with increase in PANI content in electrospinning solution. The band gap of PANI was determined to be 2.5 eV using UV-Vis spectroscopy. The electrical conductivities of the nanofibers increased with an increase in the PANI content in the nanofibers. Additionally, the sensitivity toward NH3 increased as the PANI content increased, but branched nanofibers reduced sensing response. The humidity sensitivity changed from positive to negative as the PANI content increased. The electron transport mechanism was studied by measuring the temperature dependence electrical resistivity. The negative temperature coefficient of resistance revealed a semiconducting behavior for the PANI/PEO nanofibers. The activation energy, calculated by Arrhenius plot, increased as the PANI content decreased. The power law indicated that electrons were being transported in a three dimensional matrix, and the longer hopping distance required more hopping energy for electron transport.
    Electroanalysis 03/2014; · 2.82 Impact Factor
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    ABSTRACT: A cost-effective process that combines electrospinning and a galvanic displacement reaction was utilized to synthesize ultralong hollow PbxSeyNiz nanofibers with controlled dimensions, morphology, composition, and crystal structure. Ni nanofibers were electrospun with an average diameter of 150 nm and were used as the sacrificial material for the galvanic displacement reaction. The composition and morphology of the PbxSeyNiz nanofibers were controlled during the reaction by tuning the concentration of HSeO2 + in the electrolytes. Hollow PbxSeyNiz nanofibers with smooth surfaces were obtained from the low-concentration HSeO2+ solution (i.e., 0.01 and 0.05 mM), but the hollow nanofibers synthesized from the high-concentration HSeO2 + solution (i.e., 1 mM) have rough outer surfaces with nanocrystal protrusions. The Pb content of the anofibers’ composition was varied from 3 to 42% by adjusting the HSeO2+ concentration. The thermoelectric properties of the nanofiber mats were characterized, and the highest Seebeck coefficient of approximately 449 μV/K at 300 K was found for the Pb37Se59Ni4 nanofiber mat.
    Chemistry of Materials 03/2014; 26(8):2557-2566. · 8.24 Impact Factor
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    ABSTRACT: A facile, site-specific viral-templated assembly method was used to fabricate sensitive hydrogen sulfide (H2S) gas sensors at room temperature. A gold-binding M13 bacteriophage served to organize gold nanoparticles into linear arrays which were used as seeds for subsequent nanowire formation through electroless deposition. Nanowire widths and densities within the sensors were modified by electroless deposition time and phage concentration, respectively, to tune device resistance. Chemiresistive H2S gas sensors with superior room temperature sensing performance were produced with sensitivity of 654%/ppmv, theoretical lowest detection limit of 2 ppbv, and 70% recovery within 9 min for 0.025 ppmv. The role of the viral template and associated gold-binding peptide was elucidated by removing organics using a short O2 plasma treatment followed by an ethanol dip. The template and gold-binding peptide were crucial to electrical and sensor performance. Without surface organics, the resistance fell by several orders of magnitude, the sensitivity dropped by more than a factor of 100 to 6%/ppmv, the lower limit of detection increased, and no recovery was detected with dry air flow. Viral templates provide a novel, alternative fabrication route for highly sensitive, nanostructured H2S gas sensors.
    Nanotechnology 03/2014; 25(13):135205. · 3.84 Impact Factor
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    ABSTRACT: Electrospinning was utilized to synthesize a polyaniline (PANI)/poly(ε-caprolactone) (PCL) composite in the form of nanofibers to examine its gas sensing performance. Electrical conductivity of the composite nanofibers was tailored by secondary doping with protonic acids including hydrochloride (HCl) or camphorsulfonic acid (HCSA). FT-IR and diffuse reflectance UV-vis spectroscopy were utilized to examine doping-dependent changes in the chemical structure and the protonation state of the nanofibers, respectively. The oxidation and protonation state of the composite nanofibers were shown to strongly depend on the doping agent and duration, demonstrating a simple way of controlling the electrical conductivity of the composite. PANI/PCL electrospun nanofibers having various electrical conductivities via varying dopants and doping concentrations, were configured to chemiresistors for sensing various analytes, including water vapor, NH3, and NO2. Secondary doping with Cl(-) and CSA differentially affected sensing behaviors by having distinctive optimal sensitivities. Biphasic sensitivity with respect to electrical conductivity was observed, demonstrating a facile method to enhance gas sensitivity by optimizing secondary doping. A balance between Debye length of the nanofibers and overall charge conduction may play an important role for modulating such an optimal sensitivity.
    Nanotechnology 02/2014; 25(11):115501. · 3.84 Impact Factor
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    ABSTRACT: Lead telluride (PbTe) nanostructures were synthesized by galvanic displacement reaction of electrodeposited Co thin films where the effect of [Pb2+]/[HTeO2+] ratio in the electrolyte, the thickness of sacrificial layer, and the reaction time on the surface morphology and composition were systematically investigated. The composition of PbTe nanostructures were strongly dependent on the [Pb2+]/[HTeO2+] ratio in the electrolyte where the deposited contents were varied from Te-rich (i.e., Pb20Te80) to Pb-rich (i.e., Pb69Te31) PbTe. The surface morphologies varied from x-shaped, cucumber-like, and flower-like to dendrite structures. TEM analysis showed that x-shaped PbTe nanostructures grew in a single crystalline face-centered cubic (FCC) structure along the [100] and [110] directions.
    Electrochimica Acta. 01/2014; 138:334–340.
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    ABSTRACT: The current work involves fabrication, characterization and subsequent evaluation of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) coated single walled carbon nanotubes (SWNTs) sensors for detecting analytes of interest in industrial manufacturing. By varying the conducting polymer׳s synthesis conditions in terms of charge controlled electropolymerization of the monomer EDOT in presence of the dopant PSS, the sensing performance of the PEDOT:PSS functionalized SWNT sensors was systematically optimized. Electrical characterization in terms of change in resistance, cyclic voltammetry and field-effect transistor measurements was performed to confirm the presence of PEDOT:PSS coating on SWNTs. The optimized sensors exhibited sensing properties over a wide dynamic range of concentrations towards saturated vapors of volatile organic compounds (VOCs) such as methanol, ethanol and methyl ethyl ketone (MEK) at room temperature. The limit of detection of this sensor was found to be 1.3%, 5.95% and 3% for saturated vapors of methanol, ethanol and methyl ethyl ketone (MEK) respectively. In terms of performance, when compared with bare SWNTs, these hybrid sensors exhibited better sensitivity. The underlying mechanism of sensing was also investigated by using them in chemFET mode of sensor configuration.
    Talanta 01/2014; 123:109–114. · 3.50 Impact Factor
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    ABSTRACT: In this study, TiO2 nanofibers with a high aspect ratio and a large specific surface area were synthesized using the electrospinning technique, and the effect of calcination temperature on their crystal structure, diameter, specific surface area and photocatalytic activity was systematically investigated. The electrospun, as-prepared PVP/TTIP nanofibers were several tens of micrometers in length with a diameter of 74 nm. TiO2 nanofibers with an average diameter of 50 nm were prepared after calcination at various temperatures. The calcination temperature significantly influenced the photocatalytic and material properties of TiO2 including grain size and specific surface area. When compared to other nanostructured TiO2 materials, such as commercial TiO2 nanoparticles (P25, Degussa), the TiO2 nanofibers exhibited greater photocatalytic activity for the degradation of acetaldehyde and ammonia.
    Journal of Nanoscience and Nanotechnology 01/2014; 14(10). · 1.15 Impact Factor
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    ABSTRACT: A Schottky contact-based hydrogen (H2) gas sensor operable at room temperature was constructed by assembling single-walled carbon nanotubes (SWNTs) on a substrate bridged by Pd microelectrodes in a chemiresistive/chemical field effect transistor (chemFET) configuration. The Schottky barrier (SB) is formed by exposing the Pd-SWNT interfacial contacts to H2 gas, the analyte it was designed to detect. Since a Schottky barrier height (SBH) acts as an exponential bottleneck to current flow, the electrical response of the sensor can be particularly sensitive to small changes in SBH, yielding an enhanced response to H2 gas. The sensing mechanism was analyzed by I-V and FET properties before and during H2 exposure. I-Vsd characteristics clearly displayed an equivalent back-to-back Schottky diode configuration and demonstrated the formation of a SB during H2 exposure. The I-Vg characteristics revealed a decrease in the carrier mobility without a change in carrier concentration; thus, it corroborates that modulation of a SB via H2 adsorption at the Pd-SWNT interface is the main sensing mechanism.
    ACS Applied Materials & Interfaces 12/2013; · 5.01 Impact Factor
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    ABSTRACT: The scalable, high-throughput, cost-effective synthesis of high-quality tetragonal tellurium (t-Te) nanowires by the galvanic displacement reaction of Si on a 4-in. Si wafer is demonstrated. This method does not require any heterogeneous seeds, physical templates, or surfactants. In addition, because seed nucleation and growth are both instantaneous, the synthesized nanowires had uniform lengths across the substrate. Furthermore, the effects of the deposition conditions, including the solution composition and reaction time and temperature, on the morphologies, dimensions, and crystallinities of the Te nanowires were analyzed to investigate the growth mechanism. The synthesized t-Te nanowires exhibited excellent piezoelectric properties, with the output current being as high as −75.0 nA.
    Electrochimica Acta 11/2013; 111:200-205. · 3.78 Impact Factor
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    ABSTRACT: Metal/DNA/SWNT hybrid nanostructure-based gas sensor arrays were fabricated by means of ink jet printing of metal ion chelated DNA/SWNTs on microfabricated electrodes, followed by electroless deposition to reduce metal ions to metal. DNA served as a dispersing agent to effectively solubilize pristine SWNTs in water and as metal ion chelating centers for the formation of nanoparticles. Noble metals including palladium, platinum, and gold were used because the high binding affinity toward specific analytes enhances the selectivity and sensitivity. The sensitivity and selectivity of the gas sensors toward various gases such as H2, H2S, NH3, and NO2 were determined at room temperature. Sensing results indicated the enhancement of the sensitivity and selectivity toward certain analytes by functionalizing with different metal nanoparticles (e.g., Pd/DNA/SWNTs for H2 and H2S). The combined responses give a unique pattern or signature for each analyte by which the system can identify and quantify an individual gas.
    Nanotechnology 11/2013; 24(50):505502. · 3.84 Impact Factor
  • Thin Solid Films 11/2013; · 1.60 Impact Factor
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    ABSTRACT: Bi x Sb2- x Te3 films were electrodeposited potentiostatically from acidic nitric baths at room temperature by controlling the electrodeposition parameters (i.e., the applied potential). Nearly stoichiometric Bi x Sb2- x Te3 thin films were obtained at applied potentials between -0.10 and -0.15 V versus the saturated calomel electrode (SCE). The electrical and thermoelectric properties of the as-deposited films were degraded at more negative deposition potentials; this might be attributed to the greater defect density formed. The post-annealing process in the reducing environment improved the electrical and thermoelectric properties, possibly because of a decrease in antistructure defects.
    Electronic Materials Letters 09/2013; 9(5):687-691. · 1.87 Impact Factor
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    ABSTRACT: This paper demonstrates the use of galvanic displacement to form continuous tellurium-based nanowires on DNA templates, enabling the conversion of metals, which can be deposited site-specifically, into other materials needed for device fabrication. Specifically, galvanic displacement reaction of copper and nickel nanowires is used to fabricate tellurium and bismuth telluride nanowires on lambda-DNA templates. The method is simple, rapid, highly selective and applicable to a number of different materials. In this study, continuous Ni and Cu nanowires are formed on DNA templates by seeding with Ag followed by electroless plating of the desired metal. These wires are then displaced by a galvanic displacement reaction where either Te or Bi2Te3 is deposited from an acidic solution containing HTeO2+ ions or a combination of HTeO2+ and Bi+3ions, and the metal wire is simultaneously dissolved due to oxidation. Both tellurium and bismuth telluride wires can be formed from nickel templates. In contrast, copper templates only form tellurium nanowires under the conditions considered. Therefore, the composition of the metal being displaced can be used to influence the chemistry of the resulting nanowire. Galvanic displacement of metals deposited on DNA templates has the potential to enable site-specific fabrication of a variety of materials and, thereby, make an important contribution to the advancement of useful devices via self-assembled nanotemplates.
    Langmuir 07/2013; · 4.19 Impact Factor
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    ABSTRACT: Millimeter-long one-dimensional SbxTey nanoribbons with controlled composition and dimensions (down to 16 nm) were demonstrated using lithographically patterned electrodeposition at predetermined locations. The morphology of nanoribbons was tuned by applying a pulse plating technique and addition of surfactant (i.e., CTAB) in the electrolyte. Independent of geometry, the deposit Te content decreased from 69 to 51 at. % Te with an increase in the applied potential. The electrical resistivity and field effect hole mobility were strongly dependent on the composition of the nanoribbon where the lowest electrical resistivity (7.9 × 10−4 ohm m) with highest hole mobility (24.6 cm2/V s) was observed from the Sb2Te3 nanoribbon. The temperature-dependent electrical resistance measurement shows low-temperature phase transition behaviors in the temperatures between 333 and 351 K.
    The Journal of Physical Chemistry C 07/2013; 117(33):17303-17308. · 4.81 Impact Factor
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    ABSTRACT: Non-contact direct printed conductive silver patterns with an enhanced flexural and bending strength and a proper electrical resistivity were fabricated using silver nanoplatelet inks without any surfactants for particle dispersion on a polyimide film. The microstructure, electrical resistivity, and bending strength of conductive features based on the nanoplatelets are systematically investigated and compared to nanoparticles to demonstrate superior properties. Nanoplatelets stack neatly on the substrate after non-contact direct printing, which minimizes void formation during sintering. This microstructure results in excellent resistivity on external repetitive bending stress as well as sufficiently lower electrical resistivity. It is believed to be a general conductive material to fabricate the non-contact direct printed conductive patterns with excellent mechanical stability for various flexible electronics, including solar cells, displays, RFID, and sensors.
    ACS Applied Materials & Interfaces 06/2013; · 5.01 Impact Factor
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    ABSTRACT: Label-free chemiresistive sensors based on a polypyrrole (PPy) nanoribbon (width: 500 nm, thickness: 25–100 nm) were batch-fabricated by a lithographically patterned nanowire electrodeposition (LPNE) technique. A plant pathogen specific antibody was covalently conjugated on the surface of the structure via N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC)/N-hydrosuccinimide (NHS) crosslinking. The sensing performance was investigated by the detection of cucumber mosaic virus (CMV). The sensitivity of the nano-immunosensors was enhanced by reducing the electrical conductivity from 1 to 0.005 S cm−1 or by decreasing the thickness of the nanoribbon from 100 nm to 25 nm. The reduction in the ionic strength of the pH buffer solutions (i.e., 10 mM PBS to 10 mM PB) also enhanced the sensitivity. However, the reliability and reproducibility of the sensors were significantly reduced by the buffer change. The optimum sensor showed excellent sensitivity with a low and upper detection limit of 10 ng ml−1 and 100 μg ml−1, respectively, which is much lower than the low detection limit of traditional enzyme-linked immunosorbent assays (ELISAs) (i.e., 3 μg ml−1).
    Analytical methods 05/2013; · 1.86 Impact Factor
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    ABSTRACT: In this study, Sb2Te3 films were electrodeposited potentiostatically at room temperature from acidic nitric baths in the presence of a surfactant, cetyltrimethylammonium bromide (CTAB). This resulted in improvements in the surface morphologies of the films. The thus-deposited films also exhibited better adherence to their substrates. In addition, the carrier transport properties of the Sb2Te3 films, including their electrical conductivities and Seebeck coefficient values, could be improved by annealing them at 200 °C. This was due to the formation of Te nanodots in the Sb2Te3 matrix. The resulting Sb2Te3 films with Te nanodots 10–20 nm in size and a dispersion density of 11.4 vol% exhibited a high power factor of 716.0 μW m−1 K−2, which was about two times higher than that of Sb2Te3 films that did not contain Te nanodots. The results of the study suggested that the improvements in the thermoelectric characteristics of the films were due to carrier energy filtering at the Te–Sb2Te3 interface.
    J. Mater. Chem. A. 04/2013; 1(17):5430-5435.

Publication Stats

2k Citations
530.36 Total Impact Points

Institutions

  • 2004–2014
    • University of California, Riverside
      • Department of Chemical and Environmental Engineering
      Riverside, California, United States
  • 2012
    • Korea Institute of Materials Science
      • Division of Materials Processing
      Sŏngnam, Gyeonggi Province, South Korea
  • 2011
    • Duke University
      • Department of Civil and Environmental Engineering (CEE)
      Durham, NC, United States
    • University of Delaware
      Delaware, United States
  • 2009–2011
    • Hanyang University
      • Division of Chemical Engineering and Bioengineering
      Ansan, Gyeonggi, South Korea
    • Arizona State University
      • School of Electrical, Computer and Energy Engineering
      Mesa, AZ, United States
  • 2009–2010
    • Nanjing University of Information Science & Technology
      Nan-ching, Jiangsu Sheng, China
  • 2008–2010
    • CSU Mentor
      Long Beach, California, United States
    • Gwangju Institute of Science and Technology
      • School of Environmental Science and Engineering
      Kwangju, Gwangju, South Korea
  • 2007
    • University of Pittsburgh
      • Electrical and Computer Engineering
      Pittsburgh, PA, United States
  • 1999–2007
    • University of California, Los Angeles
      • Department of Mechanical and Aerospace Engineering
      Los Angeles, CA, United States
  • 2006
    • Hanbat National University
      • Program in Applied Materials Engineering
      Taiden, Daejeon, South Korea
  • 2002
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, CA, United States