• Journal of the Korean Electrochemical Society
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• v.25 no.4
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• pp.125-133
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• 2022

Along with the increasing need for point-of-care diagnostics, development of portable, user-friendly, as well as sensitive sensors have gained intensive attention. Among various strategies, electrochromic sensors, which are electrochemically operated colorimetric sensors, have been actively studied. With their ability to report the presence and concentration of analytes by optical signals, electrochromic sensors utilize the advantages of both electrochemical and colorimetric sensors, enabling the simplification of device composition as well as convenient interpretation of results. Up to date, electrochromic sensors have been applied for a wide range of analytes, and further developments such as the introduction of flexible platforms or self-powered systems have been reported, providing a path towards the development of wearable sensor devices. In this review, various types of electrochromic sensors, according to the main strategy in which the electrochemical signals are converted to colorimetric signals, are introduced.

• Journal of Hydrogen and New Energy
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• v.16 no.1
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• pp.9-16
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• 2005

We studied the electrochromic properties of hydrated amorphous ruthenium oxide ($RuO_2{\cdot}xH_2O$) thin films using in-situ Raman spectroscopy during electrochemical charging/discharging cycles. We have found that the principal effect of hydrogen insertion into $RuO_2{\cdot}xH_2O$ is reduction of $Ru^{4+}\;to\;Ru^{3+}$, and not formation of new bonds involving hydrogen. We compared the changes in the Raman spectrum of a gasochromic $Pd/RuO_2{\cdot}xH_2O$ film as it is exposed to hydrogen gas with that of electrochemical hydrogen insertion. We tested the changes in the optical transmission of the $Pd/RuO_2{\cdot}xH_2O$ film when exposed to hydrogen gas.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.1-7
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• 2024

With the increasing demand for wearable sensors that are capable of point-of-care testing, paper-based sensors have been extensively studied. Paper is not only extremely cost-effective but also lightweight and flexible, and it is easy to apply conductive materials such as carbon and hydrophobic substances like wax to its surface. Moreover, the capillary action caused by cellulose fibers in paper allows the flow of liquid without help from external forces, making paper a particularly promising platform for wearable electrochemical sensors. Accordingly, paper-based sensors for detecting various analytes through electrochemical methods have been actively developed. Recently, paper-based electrochemical sensors that utilize electrochemiluminescence (ECL) or electrochromic materials for the optical read-out have been reported. This review introduces the basic fabrication methods and various application strategies of paper-based electrochemical sensors.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.121-121
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• 2003

NiO thin films are very attractive for use as an antiferromagnetic layer, p-type transparent conducting films, in electrochromic devices and functional sensor layer for chemical sensors, due to their excellent chemical stability, as well as optical, electrical and magnetic properties. In addition, (100)- and (111)-oriented NiO films can be used as buffer layers on which to deposit other oriented oxide films, such as c-axis-oriented perovskite-type ferromagnetic films and superconducting films, because of the similarity in symmetry of oxygen ion lattice and lattice constants between the NiO films and the oriented oxide films. Thus, controlling the crystallographic orientation and surface roughness of the NiO films for a buffer layer are very important.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.365.1-365.1
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• 2014

Cobalt oxide has excellent various properties such as high catalytic activity, antiferromagnetism, and electrochromism. So cobalt oxides offer a great potential for their applications in the various areas such as optical gas sensor, catalysts for oxidation reaction, electrochromic devices, high temperature solar selective absorbers, magnetic materials, pigment for glasses and ceramics, and negative electrodes for lithium-ion batteries. We have synthesized novel cobalt complexes by simple reaction of cobalt bistrimethylsilylamide as a starting material with a lot of conventional ligands as potential cobalt oxide precursors. The studies include the facile preparation, structural characterization, and spectroscopic analysis of the new precursors. We are making efforts to grow cobalt oxide thin films using cobalt complexes newly synthesized in this study using deposition techniques.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.33.1-33.1
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• 2009

To date, nanostructured tungsten oxides with a variety of stoichiometries, such as WO3, WO2.9, W18O49, and WO2, have been prepared, because they are promising candidates for applications such as gas sensors, photocatalysts, electrochromic devices, and field emission devices. Among them, W18O49 and WO2 have been widely studied due to their outstanding chemical sensing, catalytic, and electron emissive properties. Here we report, for the first time, a one-pot solution-phase route to synthesizing a novel composite hierarchical hollow structure without adding catalysts, surfactants, or templates. The products, consisting of a WO2 hollow core sphere surrounded by a W18O49 nanorod shell (yielding a sea urchin-like structure), were generated as discrete structures via Ostwald ripening. To our knowledge, this type of composite hierarchical core/shell structure has not been reported previously. The morphological evolution and the detailed growth mechanism were carefully studied. We also demonstrate that the size of the hollow urchins is readily tunable by controlling the reactant concentrations.Interestingly, although bulk tungsten oxides are weakly paramagnetic or diamagnetic, the as-prepared products show unusual ferromagnetic behavior atroom temperature. The urchin structures also show a very high Brunauer-Emmet-Teller (BET) surface area, suggesting that they may potentially be applied to chemical sensor or effective catalyst technologies.

• Journal of Surface Science and Engineering
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• v.29 no.6
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• pp.739-744
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• 1996

Lanthanide diphthalocyanines have interesting properties on electrochemical and chemical redox reactions. It is however, difficult to use because of thier short device life. Plasma-polymerization attends to improvement thier device life. Yb-diphthalocyanine ($YbPc_2$) polymer film was deposited in a parallel plate electrodes-type RF plasma reactor. $YbPc_2$ was sublimed into the argon plasma, and polymer film was obtained on a substrate. Radio frequency was constant of 13.56MHz. Pressure of argon gas, sublimation rate of $YbPc_2$ and RF power were variable parameters depending on film quality. Surface of polymer films include a lot of sub-micron order lumps. It was indicated that size of lumps depends on polymerization degree controled by parameters. Size of lumps and polymerization degree are increased with RF power. However, by the high RF power over 40W, polymerization degree is decreased with RF power and surface of film is rough. In condition of RF power is high, polymerization will compete with etching of film. We obtained good films for electrochromic display with RF power of 20W, argon gas pressure of 8.0 Pa and sublimationrate of $1.2 \times 10$ mol/min, and good films for gas sensor with RF power of 30W, argon gas pressure of 10.6Pa and sublimation rate of $1.2 \times 10$ mol/min.

• Journal of Sensor Science and Technology
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• v.6 no.1
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• pp.24-34
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• 1997

In this study, two different types of complementary electrochromic devices using amorphous $WO_{3}$ films as a working electrode, $V_{2}O_{5}$ film and NiO film as counter electrodes respectively were investigated. For the devices using amorphous and crystalline $V_{2}O_{5}$ films of $100{\sim}150nm$ thickness with $ITO/WO_{3}/LiClO_{4}-PC/V_{2}O_{5}/ITO$ structure, an optical modulation of $50{\sim}60%$ were obtained at a potential range of $1{\sim}2V$. It has been shown that transmittance and reflectance of light could be electrically controlled by low applied voltage. For the devices with $ITO/WO_{3}/LiClO_{4}-PC/NiO/ITO$ structure in which NiO film was deposited by a RF reactive sputtering, the optical modulation in visible light region (${\lambda}=550nm$) and in near infrared light region (${\lambda}=850nm$) were 25% and 30%, respectively.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.562-568
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• 2012

Metal nanowires can be coated on various substrates to create transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these metal nanowire based transparent conductive films is that the resistance between the nanowires is still high because of their low aspect ratio. Here, we demonstrate high-performance transparent conductive films with silver nanofiber networks synthesized by a low-cost and scalable electrospinning process followed by two-step sequential thermal treatments. First, the PVP/$AgNO_3$ precursor nanofibers, which have an average diameter of 208 nm and are several thousands of micrometers in length, were synthesized by the electrospinning process. The thermal behavior and the phase and morphology evolution in the thermal treatment processes were systematically investigated to determine the thermal treatment atmosphere and temperature. PVP/$AgNO_3$ nanofibers were transformed stepwise into PVP/Ag and Ag nanofibers by two-step sequential thermal treatments (i.e., $150^{\circ}C$ in $H_2$ for 0.5 h and $300^{\circ}C$ in Ar for 3 h); however, the fibrous shape was perfectly maintained. The silver nanofibers have ultrahigh aspect ratios of up to 10000 and a small average diameter of 142 nm; they also have fused crossing points with ultra-low junction resistances, which result in high transmittance at low sheet resistance.