• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.247-247
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• 2006

Chemical and physical synthesis routes were combined to prepare macroporous thin films of semiconducting metal-oxides such as $CaCu_{3}Ti_{4}O_{12}\;and\;TiO_{2}$ by sputtering onto (PMMA) microsphere templated substrates. Subsequently, the colloidal templates were removed by thermal decomposition. The remaining inorganic films comprised a monolayer of hollow hemispheres with diameter commensurate with that of the microspheres. This unique morphology increases the surface area and reduces the interfacial area between film and substrate. Consequently, the surface activity is markedly enhanced while deleterious interfacial effects between film and substrate are significantly reduced. Both effects are highly advantageous for gas sensing applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.164-164
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• 2013

Among multicomponent nanostructures, hybrid nanocatalysts consisting of metal nanoparticle-semiconductor junctions offer an interesting platform to study the role of metal-oxide interfaces and hot electron flows in heterogeneous catalysis. In this study, we report that hot carriers generated upon photon absorption significantly impact the catalytic activity of CO oxidation. We found that Pt-CdSe-Pt nanodumbbells exhibited a higher turnover frequency by a factor of two during irradiation by light with energy higher than the bandgap of CdSe, while the turnover rate on bare Pt nanoparticles didn't depend on light irradiation. We also found that Pt nanoparticles deposited on a GaN substrate under light irradiation exhibit changes in catalytic activity of CO oxidation that depends on the type of doping of the GaN. We suppose that hot electrons are generated upon the absorption of photons by the semiconducting nanorods or substrates, whereafter the hot electrons are injected into the Pt nanoparticles, resulting in the change in catalytic activity. We discuss the possible mechanism for how hot carrier flows generated during light irradiation affect the catalytic activity of CO oxidation.

• Ceramist
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• v.21 no.2
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• pp.38-48
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• 2018

This paper reports a comprehensive review of the state-of-the-art in research on the enhancement of sensing properties for the detection of gases in exhaled breath. Daily health monitoring and early diagnosis of specific diseases via the analysis of exhaled breath is possible. Because biomarkers in exhaled breath are emitted in a very small amount, it is necessary to develop highly sensitive gas sensors. In recent years, a number of researches have been carried out using various strategies for the enhancement of sensing properties such as doping, catalyst, hollow sphere, heterojunction, size effect. We introduced each strategy and summarized recent progress on sensing properties for detection of biomarkers in exhaled breath.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.64.1-64.1
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• 2012

Next generation displays such as high performance LCD, AMOLED, flexible display and transparent display require specific TFT back-planes. For high performance TFT back-planes, low temperature poly silicon (LTPS), and metal-oxide semiconductors are studied. Flexible TFT backplanes require low temperature processible organic semiconductors. Not only development of active semiconducting materials but also design and synthesis of semiconductor corresponding gate dielectric materials are important issues in those display back-planes. In this study, we investigate the high heat resistant polymeric gate dielectric materials for organic TFT and inorganic TFT with good insulating properties and processing chemical resistance. We also controlled and optimized surface energy and morphology of gate dielectric layers for direct printing process with solution processible organic and inorganic semiconductors.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.407.1-407.1
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• 2016

Electrochromism is defined as a phenomenon which involves persistently repeated change of optical properties between bleached state and colored state by simultaneous injection of electrons and ions, sufficient to induce an electrochemical redox process. Due to this feature, considerable progress has been made in the synthesis of electrochromic (EC) materials, improvements of EC properties in EC devices such as light shutter, smart window and variable reflectance mirrors etc. Among the variable EC materials, solid-state inorganics in particular, metal oxide semiconducting materials such as nickel oxide (NiO) have been investigated extensively. The NiO that is an anodic EC material is of special interest because of high color contrast ratio, large dynamic range and low material cost. The high performance EC devices should present the use of standard industrial production techniques to produce films with high coloration efficiency, rapid switching speed and robust reversibility. Generally, the color contrast and the optical switching speed increase drastically if high surface area is used. The structure of porous thin film provides a specific surface area and can facilitate a very short response time of the reaction between the surface and ions. The large variety of methods has been used to prepare the porous NiO thin films such as sol-gel process, chemical bath deposition and sputtering. Few studies have been reported on NiO thin films made by using sol-gel method. However, compared with dry process, wet processes that have the questions of the durability and the vestige of bleached state color limit the thin films practical use, especially when prepared by sol-gel method. In this study, we synthesis the porous NiO thin films on the fluorine doped tin oxide (FTO) glass by using sputtering and anodizing method. Also we compared electrical and optical properties of NiO thin films prepared by sol gel. The porous structure is promised to be helpful to the properties enhancement of the EC devices.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.80.1-80.1
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• 2010

A strontium titanate ($SrTiO_3$)-based material with a perovskite structure is considered to be one of the promising alternatives to $LaCrO_3$-based materials since $SrTiO_3$ perovskite shows a high chemical stability under both oxidizing and reducing atmospheres at high temperatures. $SrTiO_3$ materials exhibit an n-type semiconducting behavior when it is donor-doped and/or exposed to a reducing atmosphere. In this work, $Sr_{1-x}La_xTi_{1-y}M_yO_3$ materials doped with $La^{3+}$ in A-sites and aliovalent transition metal ions ($M^{n+}$) in B-sites were synthesized by the modified Pechini method. The X-ray diffraction analysis indicated that the materials synthesized by the Pechini process exhibited a single curbic perovskite-type structure without any impurity phases, and are tolerant, to some extent, to cation doping. The sintering behaviors of $Sr_{1-x}La_xTi_{1-y}M_yO_3$ in $H_2/N_2$ and air were characterized by dilatometry and microstructural observations. The electrical conduction mechanism and the dopant effect are discussed based on the defect structures and the electrical conductivities measured at various oxygen partial pressures and temperatures.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.142.2-142.2
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• 2018

One-dimensional metal oxide nanostructures have attracted considerable research activities owing to their strong application potential as components for nanosize electronic or optoelectronic devices utilizing superior optical and electrical properties. In which, semiconducting $SnO_2$ material with wide-bandgap Eg = 3.6 eV at room temperature, is one of the attractive candidates for optoelectronic devices operating at room temperature [1, 2], gas sensor [3, 4], and transparent conducting electrodes [5]. The synthesis and gas sensing properties of semiconducting $SnO_2$ nanomaterials have become one of important research issues since the first synthesis of SnO2 nanowires. In this study, $SnO_2$ nanowire networks were synthesized on a basis of a two-step process. In step 1, Sn spheres (30-800 nm in diameter) embedded in $SiO_2$ on a Si substrate was synthesized by a chemical vapor deposition method at $700^{\circ}C$. In step 2, using the source of these Sn spheres, $SnO_2$ nanowire (20-40 nm in diameter; $1-10{\mu}m$ in length) networks on a spherical Sn surface were synthesized by a thermal oxidation method at $800^{\circ}C$. The Au layers were pre-deposited on the surface of Sn spherical and subsequently oxidized Sn surface of Sn spherical formed SnO2 nanowires networks. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that $SnO_2$ nanowires are single crystalline. In addition, the $SnO_2$ nanowire is also a tetragonal rutile, with the preferred growth directions along [100] and a lattice spacing of 0.237 nm. Subsequently, the $NO_2$ sensing properties of the $SnO_2$ network nanowires sensor at an operating temperature of $50-250^{\circ}C$ were examined, and showed a reversible response to $NO_2$ at various $NO_2$ concentrations. Finally, details of the growth mechanism and formation of Sn spheres and $SnO_2$ nanowire networks are also discussed.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.181-185
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• 2005

We have investigated the effects of Al codoping on the structural, electrical transport, and magnetic properties of oxide diluted magnetic semiconductor $Zn_{1-x}Cr_xO$ thin films prepared by reactive sputtering. Nondoped $Zn_{0.99}Cr_{0.01}O$ thin films show semiconducting transport behavior and weak ferromagnetic characteristic. The Al doping increases the carrier concentration and results in an decrease of resistivity and metal-insulator transition behavior. With increasing carrier concentration, the magnetic properties drastically change, exhibiting a remarkable increase of the saturation magnetization. These results show carrier-enhanced ferromagnetic order in Cr-doped ZnO.

• Journal of Sensor Science and Technology
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• v.23 no.1
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• pp.15-18
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• 2014

We present gas sensing performance based on $2{\times}2$ sensor array with four different elements ($TiO_2$, $SnO_2$, $WO_3$ and $In_2O_3$ thin films) fabricated by rf sputter. Each thin film was deposited onto the selected $SiO_2$/Si substrate with Pt interdigitated electrodes (IDEs) of $5{\mu}m$ spacing which were fabricated on a $SiO_2$/Si substrate using photolithography and dry etching. For 5 ppm $NO_2$ and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, $2{\times}2$ sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multifunctional smart sensors for environmental monitoring.