Showing papers by "Ho Won Jang published in 2012"
TL;DR: This work demonstrates structurally simple but extremely efficient all oxide chemoresistive sensors with ~90% transmittance at visible wavelengths, enabling ultrahigh response to nitrogen dioxide and volatile organic compounds with detection limits down to parts per trillion levels and power consumption less than 0.2 microwatts.
Abstract: One of the top design priorities for semiconductor chemical sensors is developing simple, low-cost, sensitive and reliable sensors to be built in handheld devices However, the need to implement heating elements in sensor devices, and the resulting high power consumption, remains a major obstacle for the realization of miniaturized and integrated chemoresistive thin film sensors based on metal oxides Here we demonstrate structurally simple but extremely efficient all oxide chemoresistive sensors with ~90% transmittance at visible wavelengths Highly effective self-activation in anisotropically self-assembled nanocolumnar tungsten oxide thin films on glass substrate with indium-tin oxide electrodes enables ultrahigh response to nitrogen dioxide and volatile organic compounds with detection limits down to parts per trillion levels and power consumption less than 02 microwatts Beyond the sensing performance, high transparency at visible wavelengths creates opportunities for their use in transparent electronic circuitry and optoelectronic devices with avenues for further functional convergence
113 citations
TL;DR: In this article, four different compositions of indium-selenium compounds, In2Se3, InSe, In4Se3 and Ind4Se2, were prepared by mechanical alloying followed by spark plasma sintering and their thermoelectric properties were measured in the temperature range of 300 K to 673 K.
Abstract: Indium-selenium-based compounds have received much attention as thermoelectric materials since a high thermoelectric figure of merit of 1.48 at 705 K was observed in In4Se2.35. In this study, four different compositions of indium-selenium compounds, In2Se3, InSe, In4Se3, and In4Se2.35, were prepared by mechanical alloying followed by spark plasma sintering. Their thermoelectric properties such as electrical resistivity, Seebeck coefficient, and thermal conductivity were measured in the temperature range of 300 K to 673 K. All the In-Se compounds comprised nanoscaled structures and exhibited n-type conductivity with Seebeck coefficients ranging from −159 μV K−1 to −568 μV K−1 at room temperature.
17 citations
TL;DR: In this article, ordered mesoporous SiO 2 films were synthesized with various amounts of surfactant, and heat treatment at various temperatures was conducted with the synthesized films to confirm their thermal stabilities.
15 citations
TL;DR: In this article, ordered mesoporous SiO 2 films were applied to an interlayer dielectric in PCM as a thermal insulating layer, resulting in one-quarter lower power consumption.
9 citations
Patent•
06 Jul 2012TL;DR: In this article, a high-sensitivity transparent gas sensor and a method for manufacturing the same were presented, which includes a transparent substrate, a transparent electrode formed on the transparent substrate and a transparent gas-sensing layer.
Abstract: Disclosed are a high-sensitivity transparent gas sensor and a method for manufacturing the same. The transparent gas sensor includes a transparent substrate, a transparent electrode formed on the transparent substrate and a transparent gas-sensing layer formed on the transparent electrode. The transparent gas-sensing layer has a nanocolumnar structure having nanocolumns formed on the transparent electrode and gas diffusion pores formed between the nanocolumns.
8 citations
TL;DR: In this paper, the fabrication of organic thin-film transistors (OTFTs) with high-k gate dielectrics of Mn-doped Bi2Ti2O7 (BTO) films was reported.
Abstract: We report the fabrication of organic thin-film transistors (OTFTs) with high-k gate dielectrics of Mn-doped Bi2Ti2O7 (BTO) films. 3% Mn-doped BTO films deposited on polymer substrates by pulsed laser deposition at room temperature exhibit low leakage currents of 2.1 × 10–8 A/cm2 at an applied electric field of 0.3 MV/cm, while undoped BTO films show much higher leakage currents of 4.3 × 10–4 A/cm2. Mn doping effectively reduces the number of oxygen vacancies in the films and improves the electrical properties. Low operation voltage and significantly reduced leakage currents are demonstrated in pentacene-based OTFTs with the Mn-doped BTO gate dielectrics. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
7 citations
Patent•
15 Nov 2012TL;DR: In this paper, a hydrophobic antireflective substrate is described, and a method for manufacturing the same and a solar cell module including the same is presented, provided that the substrate has ultra-hydrophobic property corresponding to a large water droplet contact angle.
Abstract: Provided are a hydrophobic antireflective substrate, a method for manufacturing the same, and a solar cell module including the same. The hydrophobic antireflective substrate includes: a substrate; a nanostructured layer having nanostructured portions formed on the substrate and nanoporous portions formed between the nanostructured portions; and a hydrophobic coating film formed on the nanostructured portions. The method for manufacturing a hydrophobic antireflective substrate includes: forming a nanostructured layer having nanostructured portions and nanoporous portions formed between the nanostructured portions on a substrate; and forming a hydrophobic coating film on the nanostructured portions. In the hydrophobic antireflective substrate disclosed herein, a porous nanostructured layer is formed on the substrate and a hydrophobic coating film is formed on the nanostructured layer, so that the hydrophobic antireflective substrate has ultra-hydrophobic property corresponding to a large water droplet contact angle.
6 citations
TL;DR: The lattice thermal conductivities in the phase-separated alloys are lower than those in alloys without phase separation, attributable to increased boundary scattering.
Abstract: (Bi2Te3)(1-x)(PbTe)(x) binary systems near eutectic composition were prepared by melting of elemental metals and a sequential water quenching process and their microstructures and thermoelectric properties were investigated. Multiple phases such as Bi2Te3, BiPbTe and PbTe were observed due to phase separation when the composition x was higher than the eutectic point. Also the electrical conduction type of the alloys converted from p-type to n-type in the phase separated alloys. The lattice thermal conductivities in the phase-separated alloys are lower than those in alloys without phase separation, attributable to increased boundary scattering.
4 citations
TL;DR: Embossed TiO2 thin film gas sensors fabricated through highly ordered colloidal templating using O2 plasma exhibit substantially enhanced gas sensing performance as compared to those without surface treatments prior to colloidal Templating.
Abstract: We report a novel process that uses highly ordered colloidal templating to fabricate nanostructured TiO2 thin film gas sensors. An O2 plasma treatment is used to decrease the contact angle of a water droplet on a SiO2/Si substrate from 46 degrees to 3 degrees. The formation of this hydrophilic surface enhances the adhesion of polystyrene microspheres to the substrate during the spin coating of the colloidal solution, leading to a large-area colloid template of closely packed monolayer microspheres on the substrates. Embossed TiO2 thin film gas sensors fabricated through highly ordered colloidal templating using O2 plasma exhibit substantially enhanced gas sensing performance as compared to those without surface treatments prior to colloidal templating.
4 citations
Patent•
04 Sep 2012
TL;DR: In this article, a transparent conductive thin film is provided to have excellent conductivity, low resistance, and optical transmittance by doping with a specific composition ratio, i.e., AlxZn(1-x)O. In the chemical formula, 0.04 <= x <= 0.063.
Abstract: PURPOSE: A transparent conductive composition is provided to have excellent conductivity, low resistance, and optical transmittance by doping with a specific composition ratio. CONSTITUTION: A transparent conductive composition comprises a composition with a chemical formula of AlxZn(1-x)O. In the chemical formula, 0.04 <= x <= 0.063. A target for a transparent conductive thin film comprises the composition with the chemical formula. The transparent thin film comprises a composition with the chemical formula and has a light transmittance of 90% or more and a resistivity of 10^(-3) Ω·cm or less. A manufacturing method of the transparent thin film comprises a step of obtaining the target and a step of evaporating the target by sputtering at room temperature.
1 citations
TL;DR: In this article, the effect of magnetic field that brings the plasma near the substrate was compared with that of substrate heating, and it was found that stronger magnetic field is applied near substrate during sputtering, it can be expected that the ITO thin film with good electrical conductivity and high transparency is obtained at low substrate temperature.
Abstract: Korea Institute of Science and Technology, Electronic Materials Center, Seoul 136-791, Korea(Received June 15, 2012; Revised June 21, 2012; Accepted June 24, 2012)Abstract: Indium tin oxide (ITO) films were prepared using radio frequency (RF) magnetron sputtering method. magnets were equipped near the target in the sputter to bring the plasma near the target. The effect of magnetic field that brings the plasma near the substrate was compared with that of substrate heating. The effect of substrate heating on the grain size of the ITO thin film was larger than that of the magnetic field. However, the grain size of the ITO thin film was larger when the magnetic field was applied near the substrate during the sputtering process than when the substrate was not heated and the magnetic field was not applied. If stronger magnetic field is applied near the substrate during sputtering, it can be expected that the ITO thin film with good electrical conductivity and high transparency is obtained at low substrate temperature. When magnetic field of 90 Gauss was applied near the substrate during sputtering, the mobility of the ITO thin film increased from 15.2
TL;DR: In this article, the authors observed that the currentvoltage characteristics exhibit thickness dependence of electrical conductivity in -terminated heterostructures, and they found that the layers with a thickness of up 3 unit cells, result in highly insulating interfaces, whereas those with thickness of 4 unit cells and above result in conducting interfaces.
Abstract: Oxides possess several interesting properties, such as ferroelectricity, magnetism, superconductivity, and multiferroic behavior, which can effectively be used oxide electronics based on epitaxially grown heterostructures. The microscopic properties of oxide interfaces may have a strong impact on the electrical transport properties of these heterostructures. It was recently demonstrated that high electrical conductivity and mobility can be achieved in the system of an ultrathin film deposited on a -terminated substrate, which was a remarkable result because the conducting layer was at the interface between two insulators. In this study, we observe that the current-voltage characteristics exhibit thickness dependence of electrical conductivity in -terminated . We find that the layers with a thickness of up 3 unit cells, result in highly insulating interfaces, whereas those with thickness of 4 unit cells and above result in conducting interfaces.
22 May 2012
TL;DR: In this article, the authors presented a TiO2 nanohelix gas sensors with top-and-bottom electrodes configuration fabricated by oblique angle deposition (OAD) that is very simple, easy, and compatible with conventional microfabrication processes.
Abstract: We present TiO2 nanohelix gas sensors with top-and-bottom electrodes configuration fabricated by oblique angle deposition (OAD) that is very simple, easy, and compatible with conventional microfabrication processes. The combination of large surface-to-volume ratio, extremely small size (~ 22 nm) with near single crystallinity of TiO2 nanohelices, together with the top-and-bottom electrodes configuration results in a huge enhancement in gas sensing performances including ~10 times higher sensitivity, ~5 times lower detection limit, and much faster response time than the conventional thin film device. By employing this simple, cheap, and easy method, e-nose, consisting of each sensor devices with various nanostructures and metal-oxides, can be realized, having the large freedom of tuning the sensitivity of each device.
TL;DR: In this paper, the form of links between the beads in the templates is controlled by varying the plasma etching time on the templates, resulting in various templates with close-linked, nano-linked and isolated beads.
Abstract: Embossed thin films with high surface areas are achieved using soft-templates composed of monolayer polystyrene beads. The form of links between the beads in the templates is controlled by varying the plasma etching time on the templates, resulting in various templates with close-linked, nano-linked, and isolated beads. Room-temperature deposition of on the plasma-treated templates and calcination at result in embossed films with tailored links between anatase hollow hemispheres. Although all the embossed films have similar surface areas, the sensitivity of films with nano-linked hollow hemispheres to 500 ppm CO and ethanol gases are much higher than that of films with close-linked and isolated hollow hemispheres, and the detection limits of them are as low as 0.6 ppm for CO and 0.1 ppm for ethanol. The strong correlation of sensitivity with the form of links between hollow hemispheres reveals the critical role of potential barriers formed at the links. The facile, large-scale, and on-chip fabrication of embossed films with nano-linked hollow hemispheres on Si substrate and the high sensitivity without the aid of additives give us a sustainable competitive advantage over various methods for the fabrication of highly sensitive -based sensors.
TL;DR: In this article, the authors fabricated a multifunctional ceramic sensor composed of temperature and gas sensors and investigated the CO sensing properties of three dimensional nanostuctured thin film gas sensors fabricated with silica.
Abstract: Multifunctional structures with two kinds of materials have been intensively investigated in order to improve their electrical characteristic with two functions simultaneously. However, the research regarding of multifunctional ceramic sensor is still in a preliminary stage and how to integrate them with low-cost and high-yield mass production process remains a challenge issue. In this study, we fabricated the multifunctional ceramic sensor composed of temperature and gas sensors. Moreover, we investigated the CO sensing properties of three dimensional nanostuctured thin film gas sensors fabricated with silica ( nanosphere (