Showing papers by "Ho Won Jang published in 2016"

Organolead Halide Perovskites for Low Operating Voltage Multilevel Resistive Switching.

Abstract: Organolead halide perovskites are used for low-operating-voltage multilevel resistive switching. Ag/CH3 NH3 PbI3 /Pt cells exhibit electroforming-free resistive switching at an electric field of 3.25 × 10(3) V cm(-1) for four distinguishable ON-state resistance levels. The migration of iodine interstitials and vacancies with low activation energies is responsible for the low-electric-field resistive switching via filament formation and annihilation.

Wafer-scale transferable molybdenum disulfide thin-film catalysts for photoelectrochemical hydrogen production

Abstract: We demonstrate that wafer-scale, transferable, and transparent thin-film catalysts based on MoS2, which consists of cheap and earth abundant elements, can provide a low onset potential of 1 mA cm−2 at 0.17 V versus a reversible hydrogen electrode and the high photocurrent density of 24.6 mA cm−2 at 0 V for a p-type Si photocathode. c-Domains with vertically stacked (100) planes in the transferable 2H-MoS2 thin films, which are grown via a thermolysis method, act as active sites for the hydrogen evolution reaction, and photogenerated electrons are efficiently transported through the n-MoS2/p-Si heterojunction.

Size-Dependent Properties of Two-Dimensional MoS2 and WS2

Abstract: The characteristic differences between MoS2 and WS2 nanosheets and nanodots are investigated. The nanosheets were formed by liquid-phase sonication, while the nanodots were formed by breaking the nanosheets through heating the solvent ethylene glycol. The nanosheets and nanodots were approximately 0.7–2 nm thick, with slight deviation. Most of the nanosheets were longer than 100 nm, and most of the nanodots were shorter than 5 nm. As the bulk materials were transformed into nanosheets and/or nanodots, the absorption peaks and Raman peaks shifted to shorter wavelengths. Photoluminescence peaks were observed at 500 and 445 nm in the MoS2 and WS2 samples smaller than 100 nm. In the X-ray diffraction spectra, only the (002) peak was present in the nanosheets, while no peak was detected for the nanodots due to their small size. No detectable differences between the nanosheets and nanodots were observed in the transmission electron micrographs, synchrotron radiation photoemission spectra, or work function measu...

Inhibition of Ion Migration for Reliable Operation of Organolead Halide Perovskite-Based Metal/Semiconductor/Metal Broadband Photodetectors

Abstract: Organolead halide perovskites (OHPs) have attracted extensive attention as light harvesting materials for solar cells recently, because of their high charge carrier mobility, high photoconversion efficiencies, low cost, and simple methodology. Despite these advantages, the OHPs exhibit sweep-dependent hysteresis behavior in current–voltage characteristics films, deteriorating the reliability of devices based on the OHPs. This study demonstrates reliable high on/off ratio (Ion/Ioff = 104) CH3NH3PbI3 broadband photodetectors with buffer layer-free simple metal/semiconductor/metal lateral structure. At high external bias, poor on/off ratios and spikes in dark current and photocurrent are observed due to the migration of charged defect ions. The ion migration can be effectively inhibited at low external bias, and thus the devices show high Ion/Ioff ratios and spike-free dark current and photocurrent. In addition, prevention of the prepoling in the CH3NH3PbI3 films by operating at the low external bias results in pronouncedly enhanced signal-to-noise ratios even under low intensity incident light. These results strongly propose that inhibiting the migration of charged defect ions in CH3NH3PbI3 films is a key in developing reliable high performance CH3NH3PbI3-based devices.

Transition Metal Disulfide Nanosheets Synthesized by Facile Sonication Method for the Hydrogen Evolution Reaction

Abstract: Two-dimensional transition metal disulfide (TMD) nanosheets, including MoS2, WS2, TaS2, and TiS2, were used to catalyze the hydrogen evolution reaction (HER). The TMDs were exfoliated by sonication to generate nanosheet layers that were approximately a few hundred nanometers in size. X-ray diffraction and transmission electron microscope data indicated that the major plane of the exfoliated nanosheets was the (002) plane and that the hexagonal structure is maintained after exfoliation with lattice constants of 0.32 nm for MoS2 and WS2 and 0.34 nm for TaS2 and TiS2. Exfoliated MoS2, WS2, TaS2, and TiS2 loaded on Au electrodes exhibited good electrocatalytic activity with low onset potentials of ∼100, 150, 175, and 135 mV, respectively, at a current density of −1 mA/cm2. MoS2 and TiS2 exhibited the best HER performance with Tafel slopes of 94.91 and 91 mV/decade. These results indicated that TMD nanosheets have potential applications as HER catalysts for the mass production of hydrogen.

Trimodally porous SnO2 nanospheres with three-dimensional interconnectivity and size tunability: a one-pot synthetic route and potential application as an extremely sensitive ethanol detector

Abstract: The rapid and effective transfer of chemical reactants to solid surfaces through porous structures is essential for enhancing the performance of nanomaterials for various energy and environmental applications. In this paper, we report a facile one-pot spray pyrolysis method for preparing highly reactant-accessible and porous SnO2 spheres, which have three-dimensionally interconnected and size-tunable trimodal (microscale, mesoscale and macroscale) pores. For this synthetic method, macroscale polystyrene spheres and mesoscale-diameter, long carbon nanotubes were used as sacrificial templates. The promising potential of the SnO2 spheres with trimodal pores (sizes ≈3, 20 and 100 nm) was demonstrated by the unprecedentedly high response to several p.p.b. levels of ethanol. Such an ultrahigh response to ethanol is explained with respect to the hierarchical porosity and pore-size-dependent gas diffusion mechanism. Spray pyrolysis has been used to prepare tin dioxide nanospheres that contain size-tunable ‘trimodal’ pores. To enhance the performance of porous nanostructures in various energy and environmental applications involving reactions at surfaces and interfaces, it is desirable to gain precise control of multimodal pores in nanostructures. Jong-Heun Lee at Korea University and co-workers have used a simple ‘one-pot’ spray pyrolysis method to produce tin dioxide nanospheres with three levels of pore sizes. Aqueous droplets containing a metal salt, macroscale polystyrene spheres and mesoscale-diameter carbon nanotubes were subjected to pyrolysis, which decomposed the metal salt and polystyrene. Heat treatment then decomposed the carbon nanotubes. The potential of this method was demonstrated by using tin dioxide spheres containing pores with sizes of 3, 20 and 100 nanometres to detect ethanol at levels of several parts per billion. Trimodally porous SnO2 nanospheres with pore sizes of 3, 20 and 100 nm were prepared with facile one-pot spray pyrolysis and their potential for extremely sensitive ethanol detector was demonstrated. The precise control over, as well as the tuning of, multimodal pores in metal oxide nanostructures provides a new and general strategy for enhancing the performance of nanomaterials for various energy and environmental applications.

Ultrasensitive reversible oxygen sensing by using liquid-exfoliated MoS2 nanoparticles

Abstract: Two-dimensional (2D) molybdenum disulfide (MoS2) has been attracting rapidly increasing interest for application in chemoresistive gas sensors owing to its moderate band gap energy and high specific surface area. However, the mechanism of chemoresistive sensing via the adsorption and desorption of gas molecules and the influence of the shape of 2D materials are not well understood yet. Herein we investigate the oxygen sensing behavior of MoS2 microflakes and nanoparticles prepared by mechanical and liquid exfoliation, respectively. Liquid-exfoliated MoS2 nanoparticles with an increased number of edge sites present high and linear responses to a broad range of oxygen concentrations (1–100%). The energetically favorable oxygen adsorption sites, which are responsible for reversible oxygen sensing, are identified by first-principles calculations based on density functional theory. This study serves as a proof-of-concept for the gas sensing mechanism depending on the surface configuration of 2D materials and broadens the potential of 2D MoS2 in gas sensing applications.

Black Phosphorus: Critical Review and Potential for Water Splitting Photocatalyst

Abstract: A century after its first synthesis in 1914, black phosphorus has been attracting significant attention as a promising two-dimensional material in recent years due to its unique properties Nowadays, with the development of its exfoliation method, there are extensive applications of black phosphorus in transistors, batteries and optoelectronics Though, because of its hardship in mass production and stability problems, the potential of the black phosphorus in various fields is left unexplored Here, we provide a comprehensive review of crystal structure, electronic, optical properties and synthesis of black phosphorus Recent research works about the applications of black phosphorus is summarized Among them, the possibility of black phosphorous as a solar water splitting photocatalyst is mainly discussed and the feasible novel structure of photocatalysts based on black phosphorous is proposed

A wafer-scale antireflective protection layer of solution-processed TiO2 nanorods for high performance silicon-based water splitting photocathodes

Abstract: Sustainable and efficient conversion of solar energy to transportable green energy and storable fuels, hydrogen, represents a solution to the energy crisis and reduces the consumption of fossil fuels, which are mainly responsible for the rise in global temperature. Solar water splitting using semiconductors, such as silicon, is promising to satisfy the global energy demand by producing hydrogen molecules. However, the solar to hydrogen conversion efficiency of a silicon photoelectrode is suppressed by overpotential, high reflectance and/or instability in liquid electrolytes. Herein, we report the synthesis of multifunctional solution-processed TiO2 nanorods on a 4-inch p-silicon wafer with controllable heights and diameters for highly efficient water splitting photocathodes. The solution-processed passivation layer of TiO2 nanorods reduces the overpotential of the silicon photocathode due to its catalytic properties. The TiO2 NRs also dramatically improves the light absorption of silicon due to the antireflective ability of the nanorods. The reflectance of silicon is decreased from 37.5% to 1.4% and enhances the saturated photocurrent density. The Pt-decorated (1–2.5 nm diameter) TiO2 nanorods/p-Si photocathodes show a short circuit current density of up to 40 mA cm−2, an open circuit voltage ∼440 mV and incident photon to current conversion efficiency of >90% using 0.5 M H2SO4 electrolyte with simulated 1 sun irradiation. The heterostructure photocathodes are stable for more than 52 h without noticeable degradation and an ideal regenerative cell efficiency of 2.5% is achieved.

Monolayer Co3O4 Inverse Opals as Multifunctional Sensors for Volatile Organic Compounds

Abstract: Monolayers of periodic porous Co3O4 inverse opal (IO) thin films for gas-sensor applications were prepared by transferring cobalt-solution-dipped polystyrene (PS) monolayers onto sensor substrates and subsequent removal of the PS template by heat treatment. Monolayer Co3O4 IO thin films having periodic pores (d≈500 nm) showed a high response of 112.9 to 5 ppm C2H5OH at 200 °C with low cross-responses to other interfering gases. Moreover, the selective detection of xylene and methyl benzenes (xylene+toluene) could be achieved simply by tuning the sensor temperature to 250 and 275 °C, respectively, so that multiple gases can be detected with a single chemiresistor. Unprecedentedly high ethanol response and temperature-modulated control of selectivity with respect to ethanol, xylene, and methyl benzenes were attributed to the highly chemiresistive IO nanoarchitecture and to the tuned catalytic promotion of different gas-sensing reactions, respectively. These well-ordered porous nanostructures could have potential in the field of high-performance gas sensors based on p-type oxide semiconductors.

Toward High-Performance Hematite Nanotube Photoanodes: Charge-Transfer Engineering at Heterointerfaces.

Abstract: Vertically ordered hematite nanotubes are considered to be promising photoactive materials for high-performance water-splitting photoanodes. However, the synthesis of hematite nanotubes directly on conducting substrates such as fluorine-doped tin oxide (FTO)/glass is difficult to be achieved because of the poor adhesion between hematite nanotubes and FTO/glass. Here, we report the synthesis of hematite nanotubes directly on FTO/glass substrate and high-performance photoelectrochemical properties of the nanotubes with NiFe cocatalysts. The hematite nanotubes are synthesized by a simple electrochemical anodization method. The adhesion of the hematite nanotubes to the FTO/glass substrate is drastically improved by dipping them in nonpolar cyclohexane prior to postannealing. Bare hematite nanotubes show a photocurrent density of 1.3 mA/cm2 at 1.23 V vs a reversible hydrogen electrode, while hematite nanotubes with electrodeposited NiFe cocatalysts exhibit 2.1 mA/cm2 at 1.23 V which is the highest photocurrent...

Future Changes in Drought Characteristics under Extreme Climate Change over South Korea

Abstract: This study attempts to analyze several drought features in South Korea from various perspectives using a three-month standard precipitation index. In particular, this study aims to evaluate changes in spatial distribution in terms of frequency and severity of droughts in the future due to climate change, using IPCC (intergovernmental panel on climate change) GCM (general circulation model) simulations. First, the Mann-Kendall method was adopted to identify drought trends at the five major watersheds. The simulated temporal evolution of SPI (standardized precipitation index) during the winter showed significant drying trends in most parts of the watersheds, while the simulated SPI during the spring showed a somewhat different feature in the GCMs. Second, this study explored the low-frequency patterns associated with drought by comparing global wavelet power, with significance test. Future spectra decreased in the fractional variance attributed to a reduction in the interannual band from 2 to 8 years. Finally, the changes in the frequency and the severity under climate change were evaluated through the drought spell analyses. Overall features of drought conditions in the future showed a tendency to increase (about 6%) in frequency and severity of droughts during the dry season (i.e., from October to May) under climate change.

Bottom-Up Synthesis of MeSx Nanodots for Optoelectronic Device Applications

Abstract: WSx and MoSx nanodots are synthesized from (NH4)2WS4 and (NH4)2MoS4 precursors using a solvothermal method, and applied to organic photovoltaic cells (OPVs) and organic light emitting diodes (OLEDs) as hole injection layers (HILs). The optical band gaps of WSx and MoSx nanodots are 3.55 and 3.1 eV, respectively, and these nanodots show their strongest photoluminescence (PL) emission at 438 and 436 nm. The work functions of the nanodots increased from 4.3–4.4 to 5.0–5.1 eV following ultraviolet/ozone (UVO) treatment. By sandwiching thin layers of UVO-treated WSx and MoSx as HILs, the power conversion efficiency of OPVs dramatically increases from 1.51% to 3.0% and 2.95%, comparable to that of poly(3,4 ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) based devices (3.23%). This increased OPV efficiency is believed to come from the increased work function, large band gap, and PL properties of nanodots. The UVO-MoSx based OLED shows a higher maximum luminance efficiency (14.7 cd A−1) compared to PEDOT:PSS based devices (13.1 cd A−1). In addition, this study confirms that the stabilities of the OPV and OLEDs in air can be prolonged by using UVO-treated WSx or MoSx nanodots as HILs. These results demonstrate the great potential of synthesized WSx or MoSx nanodots for use as HILs in optoelectronic devices.

Compositional and Interfacial Modification of Cu2ZnSn(S,Se)4 Thin-Film Solar Cells Prepared by Electrochemical Deposition

Abstract: A highly efficient Cu2ZnSn(S,Se)4 (CZTSSe)-based thin-film solar cell (9.9 %) was prepared using an electrochemical deposition method followed by thermal annealing. The Cu–Zn–Sn alloy films was grown on a Mo-coated glass substrate using a one-pot electrochemical deposition process, and the metallic precursor films was annealed under a mixed atmosphere of S and Se to form CZTSSe thin films with bandgap energies ranging from 1.0 to 1.2 eV. The compositional modification of the S/(S+Se) ratio shows a trade-off effect between the photocurrent and photovoltage, resulting in an optimum bandgap of roughly 1.14 eV. In addition, the increased S content near the p–n junction reduces the dark current and interface recombination, resulting in a further enhancement of the open-circuit voltage. As a result of the compositional and interfacial modification, the best CZTSSe-based thin-film solar cell exhibits a conversion efficiency of 9.9 %, which is among the highest efficiencies reported so far for electrochemically deposited CZTSSe-based thin-film solar cells.

Highly photoresponsive and wavelength-selective circularly-polarized-light detector based on metal-oxides hetero-chiral thin film.

Abstract: A highly efficient circularly-polarized-light detector with excellent wavelength selectivity is demonstrated with an elegant and simple microelectronics-compatible way. The circularly-polarized-light detector based on a proper combination of the geometry-controlled TiO2-SnO2 hetero-chiral thin film as an effective chiroptical filter and the Si active layer shows excellent chiroptical response with external quantum efficiency as high as 30% and high helicity selectivity of ~15.8% in an intended wavelength range. Furthermore, we demonstrated the ability of manipulating both bandwidth and responsivity of the detector simultaneously in whole visible wavelength range by a precise control over the geometry and materials constituting hetero-chiral thin film. The high efficiency, wavelength selectivity and compatibility with conventional microelectronics processes enabled by the proposed device can result in remarkable developments in highly integrated photonic platforms utilizing chiroptical responses.

Room Temperature Deposition of Crystalline Nanoporous ZnO Nanostructures for Direct Use as Flexible DSSC Photoanode.

Abstract: A facile approach to fabricate dye-sensitized solar cells (DSSCs) is demonstrated by depositing (001) oriented zinc oxide (ZnO) nanostructures on both glass and flexible substrates at room temperature using pulsed laser deposition. Unique crystallographic characteristics of ZnO combined with highly non-equilibrium state of pulsed laser-induced ablated species enabled highly crystalline ZnO nanostructures without aid of any chemically induced additives or organic/inorganic impurities at room temperature. Film morphology as well as internal surface area is tailored by varying ambient oxygen pressure and deposition time. It is revealed that the optimization of these two experimental factors was essential for achieving structure providing large surface area as well as efficient charge collection. The DSSCs with optimized ZnO photoanodes showed overall efficiencies of 3.89 and 3.4 % on glass and polyethylene naphthalate substrates, respectively, under AM 1.5G light illumination. The high conversion efficiencies are attributed to elongated electron lifetime and enhanced electrolyte diffusion in the high crystalline ZnO nanostructures, verified by intensity-modulated voltage spectroscopy and electrochemical impedance measurements.

Comprehensive study on critical role of surface oxygen vacancies for 2DEG formation and annihilation in LaAlO3/SrTiO3 heterointerfaces

Abstract: Here we report comprehensive study of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. We observe that the oxygen deficient environment during the deposition of LAO overlayer is essentially required to create 2DEG at LAO/STO interface regardless of growth temperature from 25°C to 700°C, indicating that the oxygen-poor condition in the system is more important than the crystallinity of LAO layer. The critical thickness (2.6 nm) of 2DEG formation at a-LAO/STO heterostructure is thicker than (1.6 nm) that at c-LAO/STO. Upon ex-situ annealing at 300°C under 300 mTorr of oxygen pressure, 2DEG at a-LAO/STO interface is annihilated, while that in c-LAO/STO interface is still maintained. With combing these findings and scanning transmission electron microscope (STEM) analysis, we suggest that oxygen vacancies at the LAO surface is attributed to the origin of 2DEG formation at the LAO/STO and the crystallinity of the LAO overlayer plays a critical role in the annihilation of 2DEG at a-LAO/STO interface rather than in the formation of 2DEG. This work provides a framework to understand the importance of prohibiting the LAO surface from being oxidized for achieving thermally stable 2DEG at a-LAO/STO interface.

Effect of Amine-Based Organic Compounds on the Work-Function Decrease of Graphene

Abstract: We have demonstrated that amine and alkyl groups, applied by a simple spin-coating method, can provide an n-type doping effect on graphene sheets. The organic compounds used in this work are based on amine, phenyl amine, butylphenyl amine, benzoylphenyl amine, and tolylvinylphenyl amine groups. The increases in sheet resistance, decreases in transmittance and work function, and shifts of the G peak to higher wavenumbers and the 2D peak to lower wavenumbers in the Raman spectra indicate that graphene was doped to n-type after the graphene sheets were spin-coated by the amine-based compounds. In particular, graphene doped with butylphenyl amine showed the strongest n-type effect among all of the samples because butylphenyl amine has the strongest binding energy with graphene sheets and disperses in nonpolar solvents, suggesting that the binding energy with graphene sheets and the degree of dispersion in solvents are important factors in the doping process. Molecular calculations based on density functional ...

Thermal stability of 2DEG at amorphous LaAlO 3 /crystalline SrTiO 3 heterointerfaces

Abstract: At present, the generation of heterostructures with two dimensional electron gas (2DEG) in amorphous LaAlO3 (a-LAO)/SrTiO3 (STO) has been achieved. Herein, we analysed thermal stability of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. To create 2DEG at LAO/STO interface, regardless of growing temperature from 25 to 700 °C, we found that environment with oxygen deficient during the deposition of LAO overlayer is essentially required. That indicates that the oxygen-poor condition in the system is more essential than the crystalline nature of LAO layer. 2DEG at a-LAO/STO interface is depleted upon ex situ annealing at 300 °C under 300 Torr of oxygen pressure, while that in c-LAO/STO interface is still maintained. Our result suggests that the LAO overlayer crystallinity critically affects the thermal-annealing-induced depletion of 2DEG at a-LAO/STO interface rather than the generation of 2DEG. We clearly provide that amorphous TiOx can efficiently prevent the thermal degradation of 2DEG at the a-LAO/STO interface, which gives a cornerstone for achieving thermal-stable 2DEG at a-LAO/STO interface.

Photoactivities of Nanostructured α-Fe 2 O 3 Anodes Prepared by Pulsed Electrodeposition

Abstract: Ferric oxide (α-Fe₂O₃, hematite) is an n-type semiconductor; due to its narrow band gap (Eg = 2.1 eV), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with Fe₂O₃ is considerably lower than the theoretical values because the considerably short diffusion length (2–4 nm) of holes in Fe₂O₃ induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of α-Fe2O3 photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of α-Fe₂O₃-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of α-Fe₂O₃ anodes. It is revealed that the photocurrent density of a bare α-Fe₂O₃ anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of TiCl₃. Under optimum conditions, a modified α-Fe₂O₃ anode exhibits a maximum photocurrent density of 0.4 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified α-Fe₂O₃ anodes.

Design of Metal Oxide Hollow Structures Using Soft-templating Method for High-Performance Gas Sensors

Abstract: Semiconductor gas sensors based on metal oxide are widely used in a number of applications, from health and safety to energy effi-ciency and emission control. Nanomaterials including nanowires, nanorods, and nanoparticles have dominated the research focus in thisfield owing to their large number of surface sites that facilitate surface reactions. Recently, metal oxide hollow structures using soft tem-plates have been developed owing to their high sensing properties with large-area uniformity. Here, we provide a brief overview of metaloxide hollow structures and their gas-sensing properties from the aspects of template size, morphology, and additives. In addition, a gas-sensing mechanism and perspectives are presented. Keywords: Gas sensor, Soft-template method, Nanostructure, Hollow hemisphere, Metal decoration 1. INTRODUCTION The functional convergence of the Internet with radio frequencyidentification, sensors, and smart objects led to the era of theInternet of Things (IoT), which supplies and accesses all real-world information [1]. Sensor technology is the most importantfactor in IoT because sensors offer enormous amounts ofinformation for many types of environment. Accordingly, varioussensors such as gas, pressure, illumination, tilt, temperature, andmotion sensors have been heavily studied to more preciselymeasure and monitor changes in environments [2]. In particular,diverse applications of the gas sensor in broad fields including thedetection of air pollutants and gaseous hazards, homeland security,medical diagnosis, and fuel combustion control have acceleratedstudies for high-performance gas sensors [3-7]. Gas sensors for applications in the IoT should meet specialrequirements such as low cost, miniaturized size, ease ofintegration with electronic circuits, and high sensing performance[8]. Various gas sensors including optical, electrochemical, surfaceacoustic wave, and semiconductor metal oxide sensors have beenextensively studied to fulfill the needs of the IoT [9]. In particular,owing to their simplicity in operation, low cost, flexibility inproduction, small size, and easy integration with electroniccircuits, semiconductor gas sensors based on metal oxides arevery promising as sensing elements for IoT [10-12]. Generally, the gas-sensing properties of metal oxide aredetermined by three basic factors: utility factor, transducerfunction, and receptor function [13]. The first factor is related togas diffusion (porous structure), and the second factor is related tothe mechanism of electron transport between adjacent crystals(neck control). The receptor function is related to the ability of theoxide surface to interact with target gases (metal additives anddecoration). Over the past decade, metal oxide nanostructuressuch as nanoparticles, nanowires, nanotubes, and nanofibers withmetal catalysts have significantly improved the three basic factors,leading to high-performance gas sensors [14]. However, sincethese nanostructures are commonly synthesized using wetchemical methods or transfer methods, developing versatile andreproducible fabrication processes has remained a challenge [15]. An alternative method for achieving highly sensitive metaloxide gas sensors is a soft-template method consisting of polymermicrospheres, which is effective in fabricating long-range orderedsubmicron hollow structures of various metal oxides [16,17]. Inspite of their potential advantages, no review focused on the gas-sensing properties of metal oxide nanostructures fabricated by thesoft-template method has been published to the best of the

Gas sensor operable at room temperature and preparation method thereof

Abstract: The present invention relates to a gas sensor operable at room temperature and a preparation method thereof, and, more specifically, to a gas sensor operable at room temperature, which comprises: an interdigitated electrode (IDE) where multiple electrodes are placed in turn; a metal disulfide formed on the electrode; and, a metal nano particle formed on the metal disulfide, and a preparation method thereof.

Gas sensor comprising nanoparticles and manufacturing method of the same

Abstract: The present invention relates to a gas sensor including nanoparticles and a manufacturing method of the same. More specifically, the gas sensor includes: a substrate onto which a silicon oxide film is layered; and an electrode of metal deposited onto the silicon oxide film, wherein the electrode assumes an interdigitated electrode (IDE) pattern and includes molybdenum disulfide (MoS_2) nanoparticles in the upper portion. Meanwhile, the manufacturing method includes: a step of irradiating ultrasonic waves onto a polar organic solvent that contains the molybdenum disulfide nanoparticles; a step of obtaining a solution having the molybdenum disulfide nanoparticles dispersed inside after centrifuging then cleansing the ultrasonic wave irradiated solution; and a step of making the nanoparticles adhere to the IDE electrode by dripping the nanoparticle dispersed solution onto the IDE electrode.

Gas sensor comprising fluorinated graphene oxide and manufacturing method thereof

Abstract: The present invention relates to a gas sensor comprising graphene oxide bonded with a fluorine atom and a manufacturing method thereof and, more specifically, to a gas sensor comprising graphene oxide bonded with a fluorine atom, including substrate deposited with a silicon oxide film; an electrode formed in an interdigitated electrode (IDE) pattern in which multiple electrodes are alternately arranged on the upper part of the silicon oxide film; and graphene oxide bonded with a fluorine atom formed on the upper part of the electrode, and to a manufacturing method thereof. The present invention has the purpose of providing a gas sensor comprising graphene oxide bonded with a fluorine atom, having excellent sensitivity in gas measurement, and capable of repeating gas measurement, and the method for manufacturing the same.

Flexible graphene transparent gas sensor and manufacturing method thereof

Abstract: The present invention relates to a flexible graphene transparent gas sensor, and a method for manufacturing the same. A pair of bar-shaped graphene are provided in parallel to each other, and the graphene is formed in a center portion of the long axis of the graphene to connect the graphene provided in parallel to each other.