[Show abstract][Hide abstract] ABSTRACT: Photoelectrochemical cells have been used in photolysis of water to generate hydrogen as a clean energy source. A high efficiency electrode for photoelectrochemical cell systems was realized using a ZnO hierarchical nanostructure. A ZnO nanofiber mat structure was fabricated by electrospinning of Zn solution on the substrate, followed by oxidation; on this substrate, hydrothermal synthesis of ZnO nanorods on the ZnO nanofibers was carried out to form a ZnO hierarchical structure. The thickness of the nanofiber mat and the thermal annealing temperature were determined as the parameters for optimization. The morphology of the structures was examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The performance of the ZnO nanofiber mat and the potential of the ZnO hierarchical structures as photoelectrochemical cell electrodes were evaluated by measurement of the photoelectron conversion efficiencies under UV light. The highest photoconversion efficiency observed was 63 % with a ZnO hierarchical structure annealed at in air. The morphology and the crystalline quality of the electrode materials greatly influenced the electrode performance. Therefore, the combination of the two fabrication methods, electrospinning and hydrothermal synthesis, was successfully applied to fabricate a high performance photoelectrochemical cell electrode.
Preview · Article · Nov 2013 · Korean Journal of Materials Research
[Show abstract][Hide abstract] ABSTRACT: Porous nickel-decorated single-walled carbon nanotubes (Ni-SWCNTs) were grown on indium tin oxide (ITO)-coated glass substrate through the arc-discharge method. Oxidation followed at 400 °C in the air for 2 h to synthesize the NiO-SWCNT/ITO electrode. The Ni nanoparticles distributing among the SWCNTs were oxidized to become NiO as the effective sensing probes. The surface morphology and crystalline structure of the NiO-SWCNT/ITO electrode were characterized by SEM, EDS and Raman spectroscopy. The response of the NiO-SWCNT/ITO electrode to glucose was examined using the electrochemical method. The obtained cyclic voltammograms revealed the electrocatalytic behavior of the NiO-SWCNT/ITO electrode with glucose in 0.1 M NaOH solution. The amperometric response of the NiO-SWCNT/ITO electrode to glucose was investigated at a potential of 0.5 V in 0.1 M NaOH that showed a linear range of the detection from 1 μM to 1000 μM, as well as a low detection limit of 0.3 μM and a high sensitivity at 907 μA mM−1 cm−2.
No preview · Article · Jul 2013 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: A single-walled carbon nanotube (SWCNT)/sodium dodecylbenzenesulfonate (NaDDBS) dispersion containing a fluorosurfactant was bar-coated in order to produce a highly transparent and conductive thin film (TCF) for large-area application. The addition of a small amount of fluorosurfactant greatly reduced the surface tension of the CNT-dispersed solution, which produced a uniform film of CNTs by preventing agglomeration of CNTs during the drying process, and, furthermore, rendered bar-coating as the most practical large-area coating technique for a CNT solution. This particular fluorosurfactant addition maintained a CNT dispersion in the solution, which led to a dramatic improvement in the wettability of the CNT dispersion on the substrate towards high-performance TCF films. The thickness of the CNT films was controlled simply by adjusting the amount of CNTs in the solution. Moreover, the addition of a waterborne polymethyl methacrylate (PMMA) binder to the CNT dispersion improved the adhesion of the CNT films on a glass substrate.
[Show abstract][Hide abstract] ABSTRACT: A simple thermal oxidation of Cu thin films deposited on planar substrates established a growth of vertically aligned copper oxide (CuO) nanorods. DC sputter-deposited Cu thin films with various thicknesses were oxidized in environments of various oxygen partial pressures to control the kinetics of oxidation. This is a method to synthesize vertically aligned CuO nanorods in a relatively shorter time and at a lower cost than those of other methods such as the popular hydrothermal synthesis. Also, this is a method that does not require a catalyst to synthesize CuO nanorods. The grown CuO nanorods had diameters of ~100 nm and lengths of . We examined the morphology of the synthesized CuO nanorods as a function of the thickness of the Cu films, the gas environment, the oxidation time, the oxidation temperature, the oxygen gas flow rate, etc. The parameters all influence the kinetics of the oxidation, and consequently, the volume expansion in the films. Patterned growth was also carried out to confirm the hypothesis of the CuO nanorod protrusion and growth mechanism. It was found that the compressive stress built up in the Cu film while oxygen molecules incorporated into the film drove CuO nanorods out of the film.
No preview · Article · Jan 2013 · Korean Journal of Materials Research
[Show abstract][Hide abstract] ABSTRACT: Nanocomposites of CuO and single-wall carbon nanotubes (SWCNTs) were synthesized using an arc-discharging graphite rod that contained copper wires. Simultaneous arc discharges produced a CuO-SWCNT composite network. The crystalline structure and morphology of the CuO-SWCNT composite films were investigated using XRD, Raman spectroscopy, FE-SEM and TEM. The electrochemical properties were investigated by cyclic voltammogram and amperometric measurements in a 0.1M NaOH solution. The CuO content in the CuO-SWCNT nanocomposites was optimized for nonenzymatic glucose detection. The glucose sensing properties of the optimized CuO-SWCNT electrode showed good stability, selectivity, and linear glucose detection that ranged from 0.05 to 1800μM with a higher sensitivity of 1610μAcm(-2)mM(-1), a quick response time of 1-2s, and the lowest limit of detection at 50nM. The sensing performance was better than the pure CuO and SWCNT sensors, and the synergetic effect of the composite sensor was attributed to the high conductivity network of highly porous nanowires. The sensor also showed a good response in a human serum sample, which proves its high potential towards a commercial nonenzymatic glucose sensor.
No preview · Article · Oct 2012 · Biosensors & Bioelectronics
[Show abstract][Hide abstract] ABSTRACT: Single-walled carbon nanotubes (SWCNT) were deposited onto indium tin oxide (ITO)-coated glass using an arc-discharge method. Titanium oxide (TiO2) was coated onto the SWCNTs using a metal–organic chemical vapor deposition (MOCVD) technique. The surface morphology and crystal structure of a TiO2–SWCNT nanowire structured composite was investigated using FESEM, XRD and Raman spectra. The TiO2–SWCNT composite film was used to immobilize glucose oxidase (GOx). The immobilization of GOx onto TiO2–SWCNT composite film was characterized by FTIR spectroscopy. The glucose-sensing properties of a GOx/TiO2–SWCNT/ITO electrode was studied at −0.25 V, and it showed a linear range of detection from 10 μM to 1.40 mM in a response time of 9 s with a low detection limit of 10 μM and a sensitivity of 5.32 μA mM−1 cm−2. The Michaelis–Menten constant was 0.83 mM. The effects of interfering species like uric acid, ascorbic acid and sucrose were also studied.
No preview · Article · May 2012 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: Here, we used NO as a test gas to propose a strategy for a nanowire gas sensor with the maximum response—the lowest detection limits. The apparatus uses an open space ensemble structure of nanowires with diameters at near total-depletion. For this purpose, a series of open space nanowire structures of WO3 was fabricated with diameters varying from 35 to 82 nm, and a corresponding conduction nanowire sensor model was proposed. The nanowire structures revealed the highest response and a lowest detection limit of 30 ppb. Furthermore, the sensor response was maximum with nanowires of 40 nm, which is the diameter corresponding to total depletion conditions; the response was decreased at smaller diameters. The sensor model successfully explained the ultimate lower limits of the size effect in the nanowire sensors. To realize optimum sensor performance with the practical ensemble type nano-structures, an open space morphology is critical to remove the effect of gas diffusion throughout the structure.
Full-text · Article · Mar 2012 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: A polymer-based multi-walled carbon nanotube (MWCNT) field emission device was fabricated from a mixture of dispersed MWCNTs and an aqueous solution of polymethyl methacrylate (PMMA). When the mixture was applied to a substrate, the PMMA formed a strong composite with the MWCNTs, while strongly binding to the substrate. Process optimization was carried out to obtain high field emission performance by controlling the density of the MWCNT emitter tips under good adhesion conditions. The polymer concentration in the MWCNT dispersion and the number of spray coatings of the solution on the substrate served as the variables. The optimized polymer-based MWCNT field emission device showed a low turn-on field of 1.07V/μm, a high electric field enhancement factor of 2450, highly uniform emission, and long-term stability. The successful application of the developed emitters to a flexible polymer polyethylene terephthalate (PET) substrate was accomplished with good emission uniformity and long stability.
[Show abstract][Hide abstract] ABSTRACT: Tin oxide-single wall carbon nanotube (SWCNT) nano composites are synthesized for gas sensor application. The fabrication includes deposition of porous SWCNTs on thermally oxidized SiO2 substrates followed by rheotaxial growth of Sn and thermal oxidation at 300, 400, 500,
and 600 °C in air. The effects of oxidation temperature on morphology, microstructure, and gas sensing properties are investigated for process optimization. The tin monoxide oxidized at 400 °C showed the highest response at the operating temperature of 200 °C. Under the optimized
test condition, the composite structure showed better response than both structures of SWCNTs and thin film SnO.
Full-text · Article · Feb 2012 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: Cerium oxide nanorods (CeO(2) NRs) were synthesized without templates through a low cost and simple non-isothermal precipitation method. The structure and morphology of CeO(2) NRs were characterized by X-ray diffraction and transmission electron microscopy. The CeO(2) NRs films, deposited on indium tin oxide (ITO)-coated glass substrates through electrophoretic deposition, were used for the immobilization of glucose oxidase (GOx). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the CeO(2) NRs/ITO and GOx/CeO(2) NRs/ITO electrodes. The GOx/CeO(2) NRs/ITO electrode exhibits a linear range for the detection of glucose from 2 to 26 mM (correlation coefficient: 0.99) at 1-2s response time. Biosensor sensitivity is 0.165 μA mM(-1) cm(-2) with 100 μM detection limit. The anti-interference ability of the biosensor was also examined. The mediator-less application of CeO(2) NRs for glucose sensing was demonstrated.
No preview · Article · Jan 2012 · Biosensors & Bioelectronics
[Show abstract][Hide abstract] ABSTRACT: Zinc oxide (ZnO) hollow hemisphere (HS) and urchin-like (UL) structures were fabricated and examined for application to a gas sensor. Films of hollow ZnO-HS arrays floating over substrates were synthesized via Znsputtering onto the template of a polystyrene sphere array followed by oxidation. Growing ZnOnanorods upon HS surfaces via a hydrothermal method formed hollow ZnO–UL structures. The thicknesses of the HS films and the lengths of nanorods in the UL structures were varied to obtain the maximum response toNO gas. Both sensor structures showed a sensing of tens of parts per billion of levels of NO concentrations with good response and gas selectivity. The highest response was realized through the thinness and the open porosity of the structures. The surface depletion determined the sensor response signal for the sensor geometry with the highest response.
Full-text · Article · Dec 2011 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: Transparent conductive hybrid thin films of single-walled carbon nanotubes (SWNTs) and polymethyl methacrylate (PMMA) are fabricated using dispersions containing SWNTs and water-borne PMMA binder. The polymer binder was used as adhesion promoter between the SWNTs and the substrate. The polymer binder content in the SWNTs dispersion is varied to obtain the optimum optical transmittance, electrical conductivity, and mechanical adhesion. The PMMA and SWNT network formed the composite over substrate. The fabricated SWNTs/PMMA hybrid films are immersed in nitric acid (HNO3) and thionyl chloride (SOCl2) to improve electrical conductivity. SWNTs films with 0.2-0.6 mg/ml polymer binder have sheet resistance of 80-140 ohms/sq at a transmittance of about 80% and a strong adhesion on glass substrate. Furthermore, the electrical stability of the films is improved via the PMMA addition. This results indicates that the SWNTs/PMMA hybrid films fabricated by this method can be used as an alternative of indium tin oxide (ITO) film on flexible substrate.
No preview · Article · Jul 2011 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: A cobalt oxide tin oxide nanocomposite based gas sensor on an SiO2 substrate was fabricated. Granular thin film of tin oxide was formed by a rheotaxial growth and thermal oxidation method using dc magnetron sputtering of Sn. Nano particles of cobalt oxide were spin-coated on the tin oxide. The cobalt oxide nanoparticles were synthesized by polymer-assisted deposition method, which is a simple cost-effective versatile synthesis method for various metal oxides. The thickness of the film can be controlled over a wide range of thicknesses. The composite structures thus formed were characterized in terms of morphology and gas sensing properties for reduction gas of H2. The composites showed a highest response of 240% at 250°C upon exposure to 4% H2. This response is higher than those observed in pure SnO2 (90%) and Co3O4 (70%) thin films. The improved response with the composite structure may be related to the additional formation of electrically active defects at the interfaces. The composite sensor shows a very fast response and good reproducibility.
No preview · Article · Nov 2010 · Korean Journal of Materials Research
[Show abstract][Hide abstract] ABSTRACT: A transparent field emission device made from spray coating a single-wall carbon nanotube (SWNT) in
-dimethylformamide (DMF) was developed. Highly crystalline SWNTs were successfully synthesized using a vapor phase method.
Amorphous carbon and catalyst metal particles that remained in the SWNTs were removed using a purification process. The purified
SWNTs were diluted and dispersed in DMF using an ultrasonic bath and a magnetic stirrer. The residue was removed by centrifugation
of the SWNT DMF solution. The solution was then spray-coated to fabricate the emitter devices. The SWNT emitter has a transparency
of more than 60% and a resistance of
. The transparent field emission device shows a maximum current density of
, a low turn-on field of
, and a high field enhancement factor of 6000.
[Show abstract][Hide abstract] ABSTRACT: A polymer-assisted deposition method was used to prepare nanocomposite structures of cobalt oxide and single-walled carbon nanotubes (SWCNTs) for a gas sensor application. Scanning electron microscopy images show that the deposition morphology of Co3O4 is closely related to the viscosity and metal ion concentration in the precursor solution. X-ray diffraction data combined with Raman spectra show that the composite film has high crystalline quality. The basic sensing behavior was evaluated with NOx gas as an electron-accepting gas and H2 as an electron-donating gas. The composite shows a response of ∼200% upon exposure to 4% H2 at room temperature. This value is higher than that observed in SWCNT thin film and Co3O4 film, as well as in other pure and functionalized CNTs. The enhancement may have originated from the combination of the nature of Co3O4 particles that actively react with gases and the formation of an electrical continuum between Co3O4 and SWCNTs.
No preview · Article · Sep 2010 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous single-walled carbon nanotube (SWNT) substrate followed by a thermal oxidation process. Oxidation is done in air at a temperature range of 300–800 °C to oxidize the Cu while removing the SWNT template. The oxidation temperature determines the stoichiometry of the CuO formed, and thus the electrical property. The structures and electrical properties of the synthesized materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and current–voltage measurements. Sensing property is examined using hydrogen gas. Gas sensing mechanism and the advantages of nanowire structure as a sensor are also discussed. The best response and recovery results are observed with the CuO nanowires oxidized at 400 °C at a working temperature of 250 °C.
Full-text · Article · Apr 2010 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: Transparent conductive single-walled carbon nanotube (SWNT) film was fabricated by spraying onto polyethylene terephthalate (PET) substrates coated with a thin polymethyl methacrylate (PMMA) layer. The PMMA layer of a thickness ~1 ¿m was used as an adhesion promoter between the PET substrate and the SWNTs. The electrical conductivity of SWNT film was improved by treatments in nitric acid (HNO3) and thionyl chloride (SOCl2). The SWNT film obtained through this manufacturing method showed a sheet resistance of 150 ¿/sq with a transmittance of 80%. The film also revealed a high adhesion on the substrate, and the resistance change with the bending angle was small.
[Show abstract][Hide abstract] ABSTRACT: Thin films of single-wall carbon nanotubes (SWNT) with various thicknesses were fabricated, and their optical and electrical properties were investigated. The SWNTs of various thicknesses were directly coated in the arc-discharge chamber during the synthesis and then thermally and chemically purified. The crystalline quality of the SWNTs was improved by the purification processes as determined by Raman spectroscopy measurements. The resistance of the film is the lowest for the chemically purified SWNTs. The resistance vs. thickness measurements reveal the percolation thickness of the SWNT film to be 50 nm. Optical absorption coefficient due to Beer-Lambert is estimated to be . The film thickness for 80% transparency is about 32 nm, and the sheet resistance is 242/sq. The authors also confirmed the relation between electrical conductance and optical conductance with very good reliability by measuring the resistance and transparency measurements.
Preview · Article · Sep 2009 · Korean Journal of Materials Research