Seok-Jun Seo - Academia.edu (original) (raw)

Papers by Seok-Jun Seo

Science of Advanced Materials, 2017

The copper-iron alloy has a number of industrial applications because of its unique characteristi... more The copper-iron alloy has a number of industrial applications because of its unique characteristics that include electromagnetic shielding capability, high electrical conductivity, and good mechanical strength. In order to explore the effect of misch metal addition on the properties of gas-atomized copper-iron alloy, Cu–Fe-Misch metal powders were produced by varying the composition of Iron and misch metal. The lattice strain, mechanical properties, and electrical conductivity of the samples were analyzed after consolidating the powder with spark plasma sintering. Detailed microstructural and lattice strain investigations were performed using scanning electron microscopy, X-ray diffraction, and electron back scattered diffraction. With the addition of misch metal, the Cu grain size decreased, whereas the mechanical properties of the sintered samples increased. On the other hand, the electrical conductivity decreased remarkably. This decreased electrical conductivity with the addition of misch metal is believed to be linked with the Cu grain refinement and formation of ferromagnetic second phase particles.

Science of Advanced Materials, 2017

Ceramics International, 2019

Lactate sensors are increasingly used for applications in sports and clinical medicine, but curre... more Lactate sensors are increasingly used for applications in sports and clinical medicine, but currently have several shortcomings including low sensitivity. We demonstrate a highly sensitive and selective non-enzymatic lactate sensor based on porous nickel oxide by sol-gel based inverse micelle method. The porosity and surface area of nickel oxide depending on the calcination temperature (250, 350, and 450°C) were compared using electron microscopy and a Brunauer-Emmett-Teller (BET) surface area analyzer. Furthermore, we also compared the chemical state of Ni 3+ in porous nickel oxides, which is known to be strongly engaged with electrocatalytic lactate detection, with different calcination temperature. The sensing characteristics were assessed using an amperometric response with a three-electrode system. Owing to a relatively large surface area and high Ni 3+ / Ni 2+ ratio, NiO calcined at 250°C, exhibit maximum sensitivity at 62.35 μA/mM (cm 2), and a minimum detection of limit of 27 μM, although, it has large amount of organic residue because of low calcination temperature. In addition to its sensitivity, a porous nickel oxide electrode also displays good selectivity against other interferents such as L-ascorbic acid, uric acid, and dopamine, further supporting its potential as a non-enzymatic lactate sensor.

Science of Advanced Materials, 2016

ABSTRACT Oxide TFT arrays were fabricated on a low thermal expansion transparent plastic substrat... more ABSTRACT Oxide TFT arrays were fabricated on a low thermal expansion transparent plastic substrate by, so-called GReCoSS process (Glass-fabric Reinforced Coating Films on Surface-treated Substrate). Using this technique, a flexible oxide TFT backplane can be released from a glass carrier plate after the TFT fabrication by a simple de-bonding without using any adhesives, laser release or transfer technique.

Solid State Phenomena, 2013

The fabrication of thin-film transistor devices incorporating active semiconductors based on zinc... more The fabrication of thin-film transistor devices incorporating active semiconductors based on zinc oxynitride (ZnON) compound is presented. It is demonstrated that the addition of appropriate dopant, gallium, in ZnON, suppresses the formation of shallow donor, nitrogen vacancies, and significantly improves electrical characteristics of the resulting TFT. The Ga:ZnON devices with field-effect mobility values exceeding 50 cm2/Vs are achieved, which makes them suitable as switching or driving elements in next-generation flat-panel displays.

Materials Chemistry and Physics, 2012

ABSTRACT Mesophase silica thin film doped with in-situ formed binary terbium (Tb) complex was syn... more ABSTRACT Mesophase silica thin film doped with in-situ formed binary terbium (Tb) complex was synthesized through a simple one-step evaporation-induced self-assembly method. In this process, the precursors of rare earth complex and surfactant were added into hydrolyzed tetramethoxy-silane (TMOS) together and the inorganic/organic mesophase thin film was formed after spin coating. The mesophase structure was characterized as a 2D-hexagonal structure by X-ray diffraction (XRD) analysis. The excitation spectra (lambda(em) = 544 nm) and emission spectra (lambda(ex) = 315 nm) indicated that the binary complex. Tb(SA)(3), formed in-situ during the formation of the film. Under the UV excitation, the mesophase silica thin film showed bright and consistent green luminescence. The luminescence quantum efficiency of the hybrid thin film was confirmed to be 35.2%. (C) 2012 Elsevier B.V. All rights reserved.

Electrochemical and Solid-State Letters, 2011

ABSTRACT We fabricated solution-processed zinc tin oxide (ZTO) TFTs with sol-gel organic-inorgani... more ABSTRACT We fabricated solution-processed zinc tin oxide (ZTO) TFTs with sol-gel organic-inorganic hybrid passivation layers owing to their solution-processibility and good water and oxygen barrier property. The sol-gel organic-inorganic hybrid passivation layers reduce hysteresis of the TFTs without deterioration of performance. The gate bias stability and the environmental stability under high temperature and relative humidity are also improved compared to unpassivated and poly(methyl methacrylate) (PMMA) passivated TFTs.

Electrochemical and Solid-State Letters, 2012

ABSTRACT Sol-gel zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated at a low tempe... more ABSTRACT Sol-gel zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated at a low temperature of 250◦C using an ultraviolet (UV) photo-annealing process. A stable ZTO sol-gel solution was produced and showed considerable absorption in UV due to the incorporation of a chelating agent, acetylacetone, which also acts as a UV-activator. The UV photo-annealing and vacuum annealing improve the electrical performance of the ZTO TFT with mobility of 2 cm2/ V· s by effective dissociation of organic groups and promotion of metal-oxide-metal bonds formation, confirmed by X-ray photoelectron spectroscopy of the ZTO films.

Applied Physics Letters, 2013

The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-i... more The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-induced negative bias stability of the resulting thin film transistors were studied. As the indium ratio increases, optical absorption via sub-gap states increases, and the threshold voltage degradation under negative bias temperature stress (NBTS) with light illumination becomes more severe. By applying high pressure anneal treatments in oxygen ambient, the density of sub-gap states is reduced by an order of magnitude compared to air-annealed devices. Consequently, significant improvements are observed in the threshold voltage shifts and the stretched exponential parameters under NBTS with light illumination.

Microporous and Mesoporous Materials, 2007

Mesoporous fluorinated organosilicate films were synthesized from tetramethoxysilane and perfluor... more Mesoporous fluorinated organosilicate films were synthesized from tetramethoxysilane and perfluoroalkylsilanes (RO) 3 Si-R 0 under acidic conditions in the presence of cationic surfactant or triblock copolymer by sol-gel spin-coating. The mesoporous fluorinated organosilicate films made from perfluoroalkylsilanes (PFASs) with long perfluoroalkyl chains, which acted as a template, displayed a hexagonal mesostructure with very low concentration of surfactants, regardless of the kind of surfactants. Although most of the surfactants and organic moieties were decomposed above 550°C, the mesostructure of mesoporous fluorinated organosilicate films was maintained up to 650°C. After calcination at 550°C, their composition was similar to that of mesoporous silica films, and the cylindrical mesostructure was changed to less ordered and broken mesostructure when PFASs with long perfluoroalkyl chains were used. However, the cylindrical mesostructure was maintained when PFASs with short perfluoroalkyl chains were used. Therefore, PFASs with long perfluoroalkyl chains acted as a structure directing agent, and the chain length of PFASs affected the formation of mesostructure and thermal-induced mesostructural change. Also, the increase of calcination temperature caused the change of the composition, mesostructure, and optical property in the mesoporous fluorinated organosilicate films.

Applied Physics Letters, 2006

Single-phase Er 2 SiO 5 nanocrystal aggregates were produced on a large scale using Si nanowire ͑... more Single-phase Er 2 SiO 5 nanocrystal aggregates were produced on a large scale using Si nanowire ͑Si-NW͒ arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si ͑111͒ substrate. Afterwards, ErCl 3 ·6H 2 O dissolved ethanol solution was spin coated and annealed first at 900°C for 4 min in a flowing N 2 /O 2 environment and then at 1200°C in a flowing Ar environment for 3 min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er 2 SiO 5 oxyorthosilicate nanocrystals. The crystalline nature of Er 2 SiO 5 film and the loose nature of the aggregate result in an atomlike Er 3+ spectrum with a very narrow luminescence linewidth at 1.53 m, which together with a complete lack of temperature quenching of Er 3+ luminescence and a high Er concentration indicate a viability of this method to fabricate efficient, high-gain Si-based optical material for Si photonics.

Applied Physics Letters, 2008

Er3+ luminescence and cooperative upconversion in ErxY2-xSiO5 nanocrystal aggregates fabricated u... more Er3+ luminescence and cooperative upconversion in ErxY2-xSiO5 nanocrystal aggregates fabricated using Si nanowires is investigated. X-ray diffraction and photoluminescence spectroscopy indicate that the composition of the final nanocrystals can be varied continuously from pure Y2SiO5 to pure Er2SiO5 while keeping the crystal structure the same. Analysis of concentration and pump-power dependence of the Er3+ photoluminescence intensity and decay time shows that while cooperative upconversion occurs at high Er concentrations, the cooperative upconversion coefficient is only (2.2+/-1.1)×10-18 cm3/s at a Er concentration of 1.2×1021 cm-3. This is nearly ten times lower at more than ten times higher Er concentration than that reported from Er-doped silica and demonstrates the viability of using such silicates for compact, high-gain Si-based optical material for Si photonics.

Journal of Luminescence, 2008

Mesophase silica thin film doped with in-situ formed ternary Eu complex was synthesized by adding... more Mesophase silica thin film doped with in-situ formed ternary Eu complex was synthesized by adding ligands (DBM ¼ dibenzoylmethane, phen ¼ 1,10-phenanthroline), Eu ions (EuCl 3 Á 6H 2 O), and Pluronic P123 triblock copolymer into hydrolyzed tetramethoxysilane (TMOS). The structure of this inorganic/organic film was characterized as a 2d-hexagonal structure by X-ray diffraction (XRD) and TEM analysis. The excitation spectra (l em ¼ 612 nm) and emission spectra (l ex ¼ 325 nm) indicated that the ternary complex, Eu-DBM-phen, was formed in-situ during the formation of the film. The mesophase silica thin film doped with the in-situ formed Eu complex showed a higher quantum efficiency compared to a pure Eu(DBM) 3 phen complex and a mesophase silica thin film doped with in-situ formed binary Eu-phen complex. r

Journal of Materials Research, 2010

Thin-film transistors (TFTs) with zinc oxide channel layers were fabricated through a simple and ... more Thin-film transistors (TFTs) with zinc oxide channel layers were fabricated through a simple and low-cost solution process. Precursor solution concentration, annealing temperature, and the process were controlled for the purpose of improving the electrical properties of ZnO TFTs and analyzed in terms of microstructural scope. The fabricated ZnO films show preferential orientation of the (002) plane, which contributes to enhanced electron conduction and a dense surface. The results show that the TFT characteristics of the film are clearly affected by the microstructure. The optimized TFT operates in a depletion mode, shows n-type semiconductor behavior, and is highly transparent (>90%) within the visible light range. It exhibits a channel mobility of 9.4 cm 2 /VÁs, a subthreshold slope of 3.3 V/decade, and an on-to-off current ratio greater than 10 5 . In addition, the result of N 2 annealing shows the possibility of improvement in electrical property of the ZnO TFTs.

Sid Symposium Digest of Technical Papers, 2008

Science of Advanced Materials, 2017

The copper-iron alloy has a number of industrial applications because of its unique characteristi... more The copper-iron alloy has a number of industrial applications because of its unique characteristics that include electromagnetic shielding capability, high electrical conductivity, and good mechanical strength. In order to explore the effect of misch metal addition on the properties of gas-atomized copper-iron alloy, Cu–Fe-Misch metal powders were produced by varying the composition of Iron and misch metal. The lattice strain, mechanical properties, and electrical conductivity of the samples were analyzed after consolidating the powder with spark plasma sintering. Detailed microstructural and lattice strain investigations were performed using scanning electron microscopy, X-ray diffraction, and electron back scattered diffraction. With the addition of misch metal, the Cu grain size decreased, whereas the mechanical properties of the sintered samples increased. On the other hand, the electrical conductivity decreased remarkably. This decreased electrical conductivity with the addition of misch metal is believed to be linked with the Cu grain refinement and formation of ferromagnetic second phase particles.

Science of Advanced Materials, 2017

Ceramics International, 2019

Lactate sensors are increasingly used for applications in sports and clinical medicine, but curre... more Lactate sensors are increasingly used for applications in sports and clinical medicine, but currently have several shortcomings including low sensitivity. We demonstrate a highly sensitive and selective non-enzymatic lactate sensor based on porous nickel oxide by sol-gel based inverse micelle method. The porosity and surface area of nickel oxide depending on the calcination temperature (250, 350, and 450°C) were compared using electron microscopy and a Brunauer-Emmett-Teller (BET) surface area analyzer. Furthermore, we also compared the chemical state of Ni 3+ in porous nickel oxides, which is known to be strongly engaged with electrocatalytic lactate detection, with different calcination temperature. The sensing characteristics were assessed using an amperometric response with a three-electrode system. Owing to a relatively large surface area and high Ni 3+ / Ni 2+ ratio, NiO calcined at 250°C, exhibit maximum sensitivity at 62.35 μA/mM (cm 2), and a minimum detection of limit of 27 μM, although, it has large amount of organic residue because of low calcination temperature. In addition to its sensitivity, a porous nickel oxide electrode also displays good selectivity against other interferents such as L-ascorbic acid, uric acid, and dopamine, further supporting its potential as a non-enzymatic lactate sensor.

Science of Advanced Materials, 2016

ABSTRACT Oxide TFT arrays were fabricated on a low thermal expansion transparent plastic substrat... more ABSTRACT Oxide TFT arrays were fabricated on a low thermal expansion transparent plastic substrate by, so-called GReCoSS process (Glass-fabric Reinforced Coating Films on Surface-treated Substrate). Using this technique, a flexible oxide TFT backplane can be released from a glass carrier plate after the TFT fabrication by a simple de-bonding without using any adhesives, laser release or transfer technique.

Solid State Phenomena, 2013

The fabrication of thin-film transistor devices incorporating active semiconductors based on zinc... more The fabrication of thin-film transistor devices incorporating active semiconductors based on zinc oxynitride (ZnON) compound is presented. It is demonstrated that the addition of appropriate dopant, gallium, in ZnON, suppresses the formation of shallow donor, nitrogen vacancies, and significantly improves electrical characteristics of the resulting TFT. The Ga:ZnON devices with field-effect mobility values exceeding 50 cm2/Vs are achieved, which makes them suitable as switching or driving elements in next-generation flat-panel displays.

Materials Chemistry and Physics, 2012

ABSTRACT Mesophase silica thin film doped with in-situ formed binary terbium (Tb) complex was syn... more ABSTRACT Mesophase silica thin film doped with in-situ formed binary terbium (Tb) complex was synthesized through a simple one-step evaporation-induced self-assembly method. In this process, the precursors of rare earth complex and surfactant were added into hydrolyzed tetramethoxy-silane (TMOS) together and the inorganic/organic mesophase thin film was formed after spin coating. The mesophase structure was characterized as a 2D-hexagonal structure by X-ray diffraction (XRD) analysis. The excitation spectra (lambda(em) = 544 nm) and emission spectra (lambda(ex) = 315 nm) indicated that the binary complex. Tb(SA)(3), formed in-situ during the formation of the film. Under the UV excitation, the mesophase silica thin film showed bright and consistent green luminescence. The luminescence quantum efficiency of the hybrid thin film was confirmed to be 35.2%. (C) 2012 Elsevier B.V. All rights reserved.

Electrochemical and Solid-State Letters, 2011

ABSTRACT We fabricated solution-processed zinc tin oxide (ZTO) TFTs with sol-gel organic-inorgani... more ABSTRACT We fabricated solution-processed zinc tin oxide (ZTO) TFTs with sol-gel organic-inorganic hybrid passivation layers owing to their solution-processibility and good water and oxygen barrier property. The sol-gel organic-inorganic hybrid passivation layers reduce hysteresis of the TFTs without deterioration of performance. The gate bias stability and the environmental stability under high temperature and relative humidity are also improved compared to unpassivated and poly(methyl methacrylate) (PMMA) passivated TFTs.

Electrochemical and Solid-State Letters, 2012

ABSTRACT Sol-gel zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated at a low tempe... more ABSTRACT Sol-gel zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated at a low temperature of 250◦C using an ultraviolet (UV) photo-annealing process. A stable ZTO sol-gel solution was produced and showed considerable absorption in UV due to the incorporation of a chelating agent, acetylacetone, which also acts as a UV-activator. The UV photo-annealing and vacuum annealing improve the electrical performance of the ZTO TFT with mobility of 2 cm2/ V· s by effective dissociation of organic groups and promotion of metal-oxide-metal bonds formation, confirmed by X-ray photoelectron spectroscopy of the ZTO films.

Applied Physics Letters, 2013

The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-i... more The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-induced negative bias stability of the resulting thin film transistors were studied. As the indium ratio increases, optical absorption via sub-gap states increases, and the threshold voltage degradation under negative bias temperature stress (NBTS) with light illumination becomes more severe. By applying high pressure anneal treatments in oxygen ambient, the density of sub-gap states is reduced by an order of magnitude compared to air-annealed devices. Consequently, significant improvements are observed in the threshold voltage shifts and the stretched exponential parameters under NBTS with light illumination.

Microporous and Mesoporous Materials, 2007

Mesoporous fluorinated organosilicate films were synthesized from tetramethoxysilane and perfluor... more Mesoporous fluorinated organosilicate films were synthesized from tetramethoxysilane and perfluoroalkylsilanes (RO) 3 Si-R 0 under acidic conditions in the presence of cationic surfactant or triblock copolymer by sol-gel spin-coating. The mesoporous fluorinated organosilicate films made from perfluoroalkylsilanes (PFASs) with long perfluoroalkyl chains, which acted as a template, displayed a hexagonal mesostructure with very low concentration of surfactants, regardless of the kind of surfactants. Although most of the surfactants and organic moieties were decomposed above 550°C, the mesostructure of mesoporous fluorinated organosilicate films was maintained up to 650°C. After calcination at 550°C, their composition was similar to that of mesoporous silica films, and the cylindrical mesostructure was changed to less ordered and broken mesostructure when PFASs with long perfluoroalkyl chains were used. However, the cylindrical mesostructure was maintained when PFASs with short perfluoroalkyl chains were used. Therefore, PFASs with long perfluoroalkyl chains acted as a structure directing agent, and the chain length of PFASs affected the formation of mesostructure and thermal-induced mesostructural change. Also, the increase of calcination temperature caused the change of the composition, mesostructure, and optical property in the mesoporous fluorinated organosilicate films.

Applied Physics Letters, 2006

Single-phase Er 2 SiO 5 nanocrystal aggregates were produced on a large scale using Si nanowire ͑... more Single-phase Er 2 SiO 5 nanocrystal aggregates were produced on a large scale using Si nanowire ͑Si-NW͒ arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si ͑111͒ substrate. Afterwards, ErCl 3 ·6H 2 O dissolved ethanol solution was spin coated and annealed first at 900°C for 4 min in a flowing N 2 /O 2 environment and then at 1200°C in a flowing Ar environment for 3 min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er 2 SiO 5 oxyorthosilicate nanocrystals. The crystalline nature of Er 2 SiO 5 film and the loose nature of the aggregate result in an atomlike Er 3+ spectrum with a very narrow luminescence linewidth at 1.53 m, which together with a complete lack of temperature quenching of Er 3+ luminescence and a high Er concentration indicate a viability of this method to fabricate efficient, high-gain Si-based optical material for Si photonics.

Applied Physics Letters, 2008

Er3+ luminescence and cooperative upconversion in ErxY2-xSiO5 nanocrystal aggregates fabricated u... more Er3+ luminescence and cooperative upconversion in ErxY2-xSiO5 nanocrystal aggregates fabricated using Si nanowires is investigated. X-ray diffraction and photoluminescence spectroscopy indicate that the composition of the final nanocrystals can be varied continuously from pure Y2SiO5 to pure Er2SiO5 while keeping the crystal structure the same. Analysis of concentration and pump-power dependence of the Er3+ photoluminescence intensity and decay time shows that while cooperative upconversion occurs at high Er concentrations, the cooperative upconversion coefficient is only (2.2+/-1.1)×10-18 cm3/s at a Er concentration of 1.2×1021 cm-3. This is nearly ten times lower at more than ten times higher Er concentration than that reported from Er-doped silica and demonstrates the viability of using such silicates for compact, high-gain Si-based optical material for Si photonics.

Journal of Luminescence, 2008

Mesophase silica thin film doped with in-situ formed ternary Eu complex was synthesized by adding... more Mesophase silica thin film doped with in-situ formed ternary Eu complex was synthesized by adding ligands (DBM ¼ dibenzoylmethane, phen ¼ 1,10-phenanthroline), Eu ions (EuCl 3 Á 6H 2 O), and Pluronic P123 triblock copolymer into hydrolyzed tetramethoxysilane (TMOS). The structure of this inorganic/organic film was characterized as a 2d-hexagonal structure by X-ray diffraction (XRD) and TEM analysis. The excitation spectra (l em ¼ 612 nm) and emission spectra (l ex ¼ 325 nm) indicated that the ternary complex, Eu-DBM-phen, was formed in-situ during the formation of the film. The mesophase silica thin film doped with the in-situ formed Eu complex showed a higher quantum efficiency compared to a pure Eu(DBM) 3 phen complex and a mesophase silica thin film doped with in-situ formed binary Eu-phen complex. r

Journal of Materials Research, 2010

Thin-film transistors (TFTs) with zinc oxide channel layers were fabricated through a simple and ... more Thin-film transistors (TFTs) with zinc oxide channel layers were fabricated through a simple and low-cost solution process. Precursor solution concentration, annealing temperature, and the process were controlled for the purpose of improving the electrical properties of ZnO TFTs and analyzed in terms of microstructural scope. The fabricated ZnO films show preferential orientation of the (002) plane, which contributes to enhanced electron conduction and a dense surface. The results show that the TFT characteristics of the film are clearly affected by the microstructure. The optimized TFT operates in a depletion mode, shows n-type semiconductor behavior, and is highly transparent (>90%) within the visible light range. It exhibits a channel mobility of 9.4 cm 2 /VÁs, a subthreshold slope of 3.3 V/decade, and an on-to-off current ratio greater than 10 5 . In addition, the result of N 2 annealing shows the possibility of improvement in electrical property of the ZnO TFTs.

Sid Symposium Digest of Technical Papers, 2008