Beyong Hwan Ryu - Academia.edu (original) (raw)

Papers by Beyong Hwan Ryu

International Journal of Precision Engineering and Manufacturing-Green Technology

Screen printing has been adopted for fabricating a wide variety of electronic devices. However, t... more Screen printing has been adopted for fabricating a wide variety of electronic devices. However, the printing defects and reliability have been an obstacle for industrialization of printed electronics. In this research, the artificial intelligence (AI) model was developed and integrated with the in-house roll-to-roll screen printing system to detect smearing defect, which is one of the main defects of screen printing. The U-Net architecture was adopted, and a total of 19 models were designed with model sizes ranging from 8E + 3 to 3E + 7 number of parameters. Their performances as validation mean Intersection over Union (IoU) were analyzed, and the optimal model was chosen with a validation mean IoU of 95.1% and a number of parameters of 8E + 6. The printed line images were evaluated by the AI model for various printing conditions, such as printed line widths, printing paste premixing, printing speeds, and printed line directions, which showed that the model could effectively detect ...

ECS Meeting Abstracts, 2012

not Available.

ECS Transactions, 2011

not Available.

Chemical Physics Letters, 2004

The atomic structure of amorphous Al 2 O 3 has been determined using a molecular dynamics simulat... more The atomic structure of amorphous Al 2 O 3 has been determined using a molecular dynamics simulation. The local electronic structures of the simulated amorphous structure and of the crystalline structure of Al 2 O 3 were investigated using first principle cluster calculations. The calculated partial densities of states for the two structures are compared with their photoelectron spectra. We find that there is a local oxygen deficiency around Al atoms in amorphous Al 2 O 3 , which results in a different local electronic structure in amorphous Al 2 O 3. We also show with our calculations and photoelectron spectroscopy that Al 2 O 3 thin films have both crystalline and amorphous properties.

ACS Applied Materials & Interfaces, 2013

Nanoparticle-based, solution-processed chalcopyrite photovoltaic devices have drawn tremendous at... more Nanoparticle-based, solution-processed chalcopyrite photovoltaic devices have drawn tremendous attraction for the realization of low-cost, large-area solar cell applications. In particular, it has been recently demonstrated that the CuSe phase plays a critical role in allowing the formation of device-quality, nanoparticle-based chalcopyrite absorber layers. For further in-depth study, with the aim of understanding the thermal behavior of the CuSe phase that triggers the vigorous densification reaction, a requisite for high-performance chalcopyrite absorber layers, both multiphase (CuSe-phase including) and single-phase (CuSe-phase free) CISe nanoparticles are investigated from the viewpoint of compositional variation and crystalline structural evolution. In addition, with CuSe-phase including CISe particulate layers, the basic restrictions in thermal treatment necessary for activating effectively the CuSe-phase induced densification reaction are suggested, in conjunction with consideration on the thermal decomposition of organic additives that are inevitably incorporated in nanoparticle-based absorber layers.

Bulletin of the American Physical Society, 2005

Submitted for the MAR05 Meeting of The American Physical Society Ab initio study of the structure... more Submitted for the MAR05 Meeting of The American Physical Society Ab initio study of the structure of 1,3-butadiene on a Si(001) surface KI-JEONG KONG, BEYONG-HWAN RYU, YOUNG-MIN CHOI, JEONG-O LEE, KISEOK AHN, HYUNJU CHANG-By employing ab initio total-energy calculations we have studied the adsorption of 1,3-butadiene molecule on a dimerreconstructed Si(001) surface. We have found that the [4+2] products are thermodynamically more stable than the [2+2] products. There are basically two kinds of [4+2] products: (i) the well-known on-top di-σ configuration over a single dimer and (ii) end-bridge configurations occupying two successive dimers in the same dimer row. In [EB] configuration at one ML coverage, 1,3-butadiene molecules at opposite end of dimer bond together to form cubane (C 8 H 8)-like square geometry with one hydrogen atom at each apex, which is stabilized by the full compensation of dangling bonds and converting two π-bonds to two σ-bonds. The staggered end-bridge (s-[EB]) is also stable by strain release. By comparing the simulated STM images and experimental ones, we pointed out that the [EB] configuration shows similar feature to that attributed as [2+2] configuration in previous experiments. The calculated core-level shifts(CLS) of C 1s orbital show little difference between peak from interface C atom bonded directly to silicon and that from surface C atom with unsaturated double bond.

Chemistry of Materials, 2016

The conductive nanomaterials applicable to unconventional printing techniques have attracted the ... more The conductive nanomaterials applicable to unconventional printing techniques have attracted the tremendous attention, and in particular, cost-effective copper-based electrode materials have been recognized a viable candidate to replace the expensive silver counterpart. In this study, we synthesize newly-designed Cu core/Cu 10 Sn 3 shell nanoparticles, as an additive material for overcoming the critical drawbacks in Cu nanoparticle-based electrodes, in combination with a large-area processable, continuous photonic sintering process in a time scale of 10-3 sec. By virtue of a low melting-point nature of Cu 10 Sn 3 phase, the facile electrode fabrication process is easily triggered, evolving the resistivities of 27.8 and 12.2 µΩ•cm under energy dose conditions of 0.97 and 1.1 J/cm 2 , respectively, at which highly conductive electrodes are not obtainable from phase-pure Cu nanoparticles. The mixture suspension of Cu and Cu/Cu 10 Sn 3 nanoparticles enables for roll-to-roll processable, highly uniform Cu-based electrodes (with a sheet resistance and a standard deviation of 1.21 and 0.29 Ω/square, respectively) even on vulnerable polyethylene naphthalate (PEN) substrate, while the electrodes derived from Cu 10 Sn 3 phase-free Cu nanoparticles suffer from non-uniform characteristics and even a partially insulating nature. The practical applicability of Cu/Cu 10 Sn 3 core/shell nanoparticles is demonstrated with the fabrication of a touch screen panel and an antenna for wireless power transmission.

J. Mater. Chem. C, 2014

Highly flexible, rollable, printable Ag conductive features are generated on PET and paper substr... more Highly flexible, rollable, printable Ag conductive features are generated on PET and paper substrates through instant continuous photonic sintering for olate-terminated Ag nanoparticles.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry C, 2013

Multiphase CuInSe 2 (CISe) nanoparticles including the secondary CuSe phase are synthesized by a ... more Multiphase CuInSe 2 (CISe) nanoparticles including the secondary CuSe phase are synthesized by a polyol-based, microwave-assisted solvothermal method. It is demonstrated that the reaction chemistry involving the formation of the CISe phase is adjusted depending on the heretofore unrecognized chemical nature of polyol solvent, allowing for the formation of secondary CuSe phaseincorporated multiphase CISe nanoparticles. The critical role of CuSe phase in generating the pore-free, dense CISe absorber layer for a high performance thin-film photovoltaic device is investigated through the comparative study on CISe absorber layers derived from both multiphase and single phase CISe nanoparticles.

The Journal of Physical Chemistry B, 2005

First principles calculations are used to predict the stability and electronic structures of SnS ... more First principles calculations are used to predict the stability and electronic structures of SnS 2 nanotubes. Optimization of several structures and their corresponding strain energies confirm the stability of SnS 2 nanotube structures. Band structure calculations show that SnS 2 nanotubes could have moderate band gaps regardless of their chirality. It suggests that SnS 2 nanotubes would be well-suited to use as semiconductor wires in nanoelectronic devices if they are synthesized. Adsorption of NH 3 onto SnS 2 is also investigated and discussed with regard to potential sensor application.

Journal of the American Chemical Society, 2005

Journal of Materials Chemistry, 2011

Precursor Solution Synthesis. All reagents, zinc acetate dihydrate (Zn(C 2 H 3 O 2) 2 •2H 2 O, 98... more Precursor Solution Synthesis. All reagents, zinc acetate dihydrate (Zn(C 2 H 3 O 2) 2 •2H 2 O, 98%), indium nitrate hydrate (In(NO 3) 3 •H 2 O, 99.9%), and gallium nitrate hydrate (Ga(NO 3) 3 •H 2 O, 99.9%), ethylene glycol (HOCH 2 CH 2 OH, anhydrous 99.8%), monoethanolamine (NH 2 CH 2 CH 2 OH, 99%), and 2-methoxyethanol (CH 3 OCH 2 CH 2 OH, anhydrous 99.8%) were purchased from Aldrich and used without additional purification. 0.375 M metal precursor solutions were prepared in 2-methoxyethanol including the different amount of ethylene glycol. The composition of ethylene glycol was varied from 0 to 30 vol%, and chemical composition ratio of IGZO precursor solution was In:Ga:Zn = 63:10:27. Monoethanolamine and DI-water were additionally incorporated as a stabilizer and a reactant for hydrolysis reaction, respectively. The prepared clear solutions were stirred for 3 hr at room temperature prior to spin coating. Transistor Fabrication and Electrical Performance Characterization. Doped silicon substrate with a 100 nm-thick thermal SiO 2 layer, used as a gate dielectric, was sonicated with absolute ethanol and dried with an N 2 stream, followed by UV/O 3 treatment for 5 min.

Journal of Colloid and Interface Science, 1996

Effects of Organic Solvents in the Intercalation of Octylamine into H-magadiite Biddy (5). Materi... more Effects of Organic Solvents in the Intercalation of Octylamine into H-magadiite Biddy (5). Materials used were silica gel (Wakogel Q-63) and analytical reagent grades of NaOH and Na 2 CO 3. The reaction was carried out at The intercalation of octylamine into H-magadiite was investi-150ЊC for 72 h in a stainless steel autoclave under autogenous pressure gated in n-hexane, hexadecane, 2,2,4-TMP, and mesitylene at without stirring using molar ratios of SiO 2 :NaOH:Na 2 CO 3 :H 2 O Å room temperature. Equilibrium of uptake is reached after 48 hr 15:1:2:300. The reaction product was separated from the mother liquid for all solvents. Uptake increased with increased of concentraby filtration, washed with deionized water, and then dried in air at 40ЊC. tion of octylamine and also exhibited the influence of the specific H-magadiite was prepared by titration of Na-magadiite with 0.1 N HCl solvent used. The basal spacings of organic solvent / octylammby the method of Lagaly et al. (13). A suspension of 40 g of Naonium-magadiite gels were shown to increase by 2-8 Å commagadiite per 500 ml of deionized water was stirred for 1 hr. The suspenpared with those of octylammonium magadiite gel prepared sion was then titrated with 0.1 N HCl to a final pH of 2.0, and then with no solvent. The results suggest that gallery height can be maintained at the same value for additional 24 h. The H-magadiite was affected by the solvation of intercalated octylamine as well recovered by filtering, washed with deionized water until Cl-free, and then dried in air at 40ЊC. as by the steric effect of solvated molecules.

Japanese Journal of Applied Physics, 2003

IEEE Transactions on Magnetics, 2009

Applied Physics Letters, 2005

We investigated the effect of humidity on the electrical transport properties of single-walled ca... more We investigated the effect of humidity on the electrical transport properties of single-walled carbon nanotube field effect transistors (SWNT-FETs). Water molecules are found to behave as electron donors to the nanotube: Current through the p-type carbon nanotube device is found to decrease under a modest humidity, and starts to increase as the humidity increases over 65%, which is believed to be due to the opening of electron channels. Through first principles calculations based on the density functional theory, we found that water molecules can donate electrons to the carbon nanotube. Moreover, a hydrogen-bonded water monolayer will be formed around the nanotube at fully covered conditions. We suggest that this result could provide a systematic understanding of the humidity effect on SWNT-FETs, which has been believed to be essential in the development of nanotube-based sensors.

Nanoscale, Jan 5, 2017

The recent development of strain sensor devices which can actively monitor human body motion has ... more The recent development of strain sensor devices which can actively monitor human body motion has attracted tremendous attention, for application in various wearable electronics and human-machine interfaces. In this study, as materials for strain sensor devices, we exploit the low-cost, carbon-based, 3-dimensional (3D) printable composite dough. The dough is prepared via a chemical method based on the formation of electrostatic assemblies between 1-dimensional, amine-functionalized, multi-walled carbon nanotubes and 2-dimensional graphene oxides. The resulting composite dough has an extremely high storage modulus, which allows a vertically-stackable, 3D printing process for fabricating strain sensor devices on various dense, porous and structured substrates. The device performance parameters, including gauge factor, hysteresis, linearity, and overshooting behavior are found to be adjustable by controlling the printing process parameters. The fabricated strain sensor devices demonstra...

Journal of Materials Chemistry, 2011

Synthesis of Cu/CuO core-shell Nanoparticles. Cu nanoparticles were synthesized via chemical redu... more Synthesis of Cu/CuO core-shell Nanoparticles. Cu nanoparticles were synthesized via chemical reduction of Cu ions in toluene (C 6 H 5 CH 3 , Aldrich, anhydrous 99.8%) under inert atmosphere. To prevent the interparticular agglomeration and surface oxidation, oleic acid (C 18 H 34 O 2 , Aldrich, 99%) was incorporated as a surface capping molecule and hydrazine (NH 2 NH 2 , Junsei, 98%) was used as a reducing agent. 16.6 g of Cu acetate (Cu(CO 2 CH 3) 2 , Aldrich, 98%), 10 g of oleic acid, and 16.6 g of hydrazine were added into a three-neck round-bottomed flask containing 100 mL of toluene. The flask was fitted with a reflux condenser and mechanical stirrer. The solution was purged with nitrogen for at least 30 min and then heated to 100 o C. Reaction was continued for 120 min and then cooled to room temperature. Then, the synthesized Cu nanoparticles were separated by centrifugation and washed with ethanol. The resulting Cu nanoparticles were well-dispersed in toluene, but not in aqueous medium. To endow the water-compatibility, we modified the surface of synthesized Cu nanoparticles by dipping Cu nanoparticles in methanol-based solution in which 6 wt% of carboxyl-terminated anionic polyelectrolyte, 16 wt% of mixture of polyoxylethylene oleylamine ether (Wako, M w = 1,000) and oxalic acid (C 2 H 2 O 4 , Aldrich, 99%) are dissolved. After reaction for 30 min under nitrogen atmosphere, the surface

Langmuir, 2011

With the aim of inkjet printing highly conductive and well-defined Cu features on plastic substra... more With the aim of inkjet printing highly conductive and well-defined Cu features on plastic substrates, aqueous based Cu ink is prepared for the first time using water-soluble Cu nanoparticles with a very thin surface oxide layer. Owing to the specific properties, high surface tension and low boiling point, of water, the aqueous based Cu ink endows a variety of advantages over conventional Cu inks based on organic solvents in printing narrow conductive patterns without irregular morphologies. It is demonstrated how the design of aqueous based ink affects the basic properties of printed conductive features such as surface morphology, microstructure, conductivity, and line width. The long-term stability of aqueous based Cu ink against oxidation is analyzed through an X-ray photoelectron spectroscopy (XPS) based investigation on the evolution of the surface oxide layer in the aqueous based ink.

International Journal of Precision Engineering and Manufacturing-Green Technology

Screen printing has been adopted for fabricating a wide variety of electronic devices. However, t... more Screen printing has been adopted for fabricating a wide variety of electronic devices. However, the printing defects and reliability have been an obstacle for industrialization of printed electronics. In this research, the artificial intelligence (AI) model was developed and integrated with the in-house roll-to-roll screen printing system to detect smearing defect, which is one of the main defects of screen printing. The U-Net architecture was adopted, and a total of 19 models were designed with model sizes ranging from 8E + 3 to 3E + 7 number of parameters. Their performances as validation mean Intersection over Union (IoU) were analyzed, and the optimal model was chosen with a validation mean IoU of 95.1% and a number of parameters of 8E + 6. The printed line images were evaluated by the AI model for various printing conditions, such as printed line widths, printing paste premixing, printing speeds, and printed line directions, which showed that the model could effectively detect ...

ECS Meeting Abstracts, 2012

not Available.

ECS Transactions, 2011

not Available.

Chemical Physics Letters, 2004

The atomic structure of amorphous Al 2 O 3 has been determined using a molecular dynamics simulat... more The atomic structure of amorphous Al 2 O 3 has been determined using a molecular dynamics simulation. The local electronic structures of the simulated amorphous structure and of the crystalline structure of Al 2 O 3 were investigated using first principle cluster calculations. The calculated partial densities of states for the two structures are compared with their photoelectron spectra. We find that there is a local oxygen deficiency around Al atoms in amorphous Al 2 O 3 , which results in a different local electronic structure in amorphous Al 2 O 3. We also show with our calculations and photoelectron spectroscopy that Al 2 O 3 thin films have both crystalline and amorphous properties.

ACS Applied Materials & Interfaces, 2013

Nanoparticle-based, solution-processed chalcopyrite photovoltaic devices have drawn tremendous at... more Nanoparticle-based, solution-processed chalcopyrite photovoltaic devices have drawn tremendous attraction for the realization of low-cost, large-area solar cell applications. In particular, it has been recently demonstrated that the CuSe phase plays a critical role in allowing the formation of device-quality, nanoparticle-based chalcopyrite absorber layers. For further in-depth study, with the aim of understanding the thermal behavior of the CuSe phase that triggers the vigorous densification reaction, a requisite for high-performance chalcopyrite absorber layers, both multiphase (CuSe-phase including) and single-phase (CuSe-phase free) CISe nanoparticles are investigated from the viewpoint of compositional variation and crystalline structural evolution. In addition, with CuSe-phase including CISe particulate layers, the basic restrictions in thermal treatment necessary for activating effectively the CuSe-phase induced densification reaction are suggested, in conjunction with consideration on the thermal decomposition of organic additives that are inevitably incorporated in nanoparticle-based absorber layers.

Bulletin of the American Physical Society, 2005

Submitted for the MAR05 Meeting of The American Physical Society Ab initio study of the structure... more Submitted for the MAR05 Meeting of The American Physical Society Ab initio study of the structure of 1,3-butadiene on a Si(001) surface KI-JEONG KONG, BEYONG-HWAN RYU, YOUNG-MIN CHOI, JEONG-O LEE, KISEOK AHN, HYUNJU CHANG-By employing ab initio total-energy calculations we have studied the adsorption of 1,3-butadiene molecule on a dimerreconstructed Si(001) surface. We have found that the [4+2] products are thermodynamically more stable than the [2+2] products. There are basically two kinds of [4+2] products: (i) the well-known on-top di-σ configuration over a single dimer and (ii) end-bridge configurations occupying two successive dimers in the same dimer row. In [EB] configuration at one ML coverage, 1,3-butadiene molecules at opposite end of dimer bond together to form cubane (C 8 H 8)-like square geometry with one hydrogen atom at each apex, which is stabilized by the full compensation of dangling bonds and converting two π-bonds to two σ-bonds. The staggered end-bridge (s-[EB]) is also stable by strain release. By comparing the simulated STM images and experimental ones, we pointed out that the [EB] configuration shows similar feature to that attributed as [2+2] configuration in previous experiments. The calculated core-level shifts(CLS) of C 1s orbital show little difference between peak from interface C atom bonded directly to silicon and that from surface C atom with unsaturated double bond.

Chemistry of Materials, 2016

The conductive nanomaterials applicable to unconventional printing techniques have attracted the ... more The conductive nanomaterials applicable to unconventional printing techniques have attracted the tremendous attention, and in particular, cost-effective copper-based electrode materials have been recognized a viable candidate to replace the expensive silver counterpart. In this study, we synthesize newly-designed Cu core/Cu 10 Sn 3 shell nanoparticles, as an additive material for overcoming the critical drawbacks in Cu nanoparticle-based electrodes, in combination with a large-area processable, continuous photonic sintering process in a time scale of 10-3 sec. By virtue of a low melting-point nature of Cu 10 Sn 3 phase, the facile electrode fabrication process is easily triggered, evolving the resistivities of 27.8 and 12.2 µΩ•cm under energy dose conditions of 0.97 and 1.1 J/cm 2 , respectively, at which highly conductive electrodes are not obtainable from phase-pure Cu nanoparticles. The mixture suspension of Cu and Cu/Cu 10 Sn 3 nanoparticles enables for roll-to-roll processable, highly uniform Cu-based electrodes (with a sheet resistance and a standard deviation of 1.21 and 0.29 Ω/square, respectively) even on vulnerable polyethylene naphthalate (PEN) substrate, while the electrodes derived from Cu 10 Sn 3 phase-free Cu nanoparticles suffer from non-uniform characteristics and even a partially insulating nature. The practical applicability of Cu/Cu 10 Sn 3 core/shell nanoparticles is demonstrated with the fabrication of a touch screen panel and an antenna for wireless power transmission.

J. Mater. Chem. C, 2014

Highly flexible, rollable, printable Ag conductive features are generated on PET and paper substr... more Highly flexible, rollable, printable Ag conductive features are generated on PET and paper substrates through instant continuous photonic sintering for olate-terminated Ag nanoparticles.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry C, 2013

Multiphase CuInSe 2 (CISe) nanoparticles including the secondary CuSe phase are synthesized by a ... more Multiphase CuInSe 2 (CISe) nanoparticles including the secondary CuSe phase are synthesized by a polyol-based, microwave-assisted solvothermal method. It is demonstrated that the reaction chemistry involving the formation of the CISe phase is adjusted depending on the heretofore unrecognized chemical nature of polyol solvent, allowing for the formation of secondary CuSe phaseincorporated multiphase CISe nanoparticles. The critical role of CuSe phase in generating the pore-free, dense CISe absorber layer for a high performance thin-film photovoltaic device is investigated through the comparative study on CISe absorber layers derived from both multiphase and single phase CISe nanoparticles.

The Journal of Physical Chemistry B, 2005

First principles calculations are used to predict the stability and electronic structures of SnS ... more First principles calculations are used to predict the stability and electronic structures of SnS 2 nanotubes. Optimization of several structures and their corresponding strain energies confirm the stability of SnS 2 nanotube structures. Band structure calculations show that SnS 2 nanotubes could have moderate band gaps regardless of their chirality. It suggests that SnS 2 nanotubes would be well-suited to use as semiconductor wires in nanoelectronic devices if they are synthesized. Adsorption of NH 3 onto SnS 2 is also investigated and discussed with regard to potential sensor application.

Journal of the American Chemical Society, 2005

Journal of Materials Chemistry, 2011

Precursor Solution Synthesis. All reagents, zinc acetate dihydrate (Zn(C 2 H 3 O 2) 2 •2H 2 O, 98... more Precursor Solution Synthesis. All reagents, zinc acetate dihydrate (Zn(C 2 H 3 O 2) 2 •2H 2 O, 98%), indium nitrate hydrate (In(NO 3) 3 •H 2 O, 99.9%), and gallium nitrate hydrate (Ga(NO 3) 3 •H 2 O, 99.9%), ethylene glycol (HOCH 2 CH 2 OH, anhydrous 99.8%), monoethanolamine (NH 2 CH 2 CH 2 OH, 99%), and 2-methoxyethanol (CH 3 OCH 2 CH 2 OH, anhydrous 99.8%) were purchased from Aldrich and used without additional purification. 0.375 M metal precursor solutions were prepared in 2-methoxyethanol including the different amount of ethylene glycol. The composition of ethylene glycol was varied from 0 to 30 vol%, and chemical composition ratio of IGZO precursor solution was In:Ga:Zn = 63:10:27. Monoethanolamine and DI-water were additionally incorporated as a stabilizer and a reactant for hydrolysis reaction, respectively. The prepared clear solutions were stirred for 3 hr at room temperature prior to spin coating. Transistor Fabrication and Electrical Performance Characterization. Doped silicon substrate with a 100 nm-thick thermal SiO 2 layer, used as a gate dielectric, was sonicated with absolute ethanol and dried with an N 2 stream, followed by UV/O 3 treatment for 5 min.

Journal of Colloid and Interface Science, 1996

Effects of Organic Solvents in the Intercalation of Octylamine into H-magadiite Biddy (5). Materi... more Effects of Organic Solvents in the Intercalation of Octylamine into H-magadiite Biddy (5). Materials used were silica gel (Wakogel Q-63) and analytical reagent grades of NaOH and Na 2 CO 3. The reaction was carried out at The intercalation of octylamine into H-magadiite was investi-150ЊC for 72 h in a stainless steel autoclave under autogenous pressure gated in n-hexane, hexadecane, 2,2,4-TMP, and mesitylene at without stirring using molar ratios of SiO 2 :NaOH:Na 2 CO 3 :H 2 O Å room temperature. Equilibrium of uptake is reached after 48 hr 15:1:2:300. The reaction product was separated from the mother liquid for all solvents. Uptake increased with increased of concentraby filtration, washed with deionized water, and then dried in air at 40ЊC. tion of octylamine and also exhibited the influence of the specific H-magadiite was prepared by titration of Na-magadiite with 0.1 N HCl solvent used. The basal spacings of organic solvent / octylammby the method of Lagaly et al. (13). A suspension of 40 g of Naonium-magadiite gels were shown to increase by 2-8 Å commagadiite per 500 ml of deionized water was stirred for 1 hr. The suspenpared with those of octylammonium magadiite gel prepared sion was then titrated with 0.1 N HCl to a final pH of 2.0, and then with no solvent. The results suggest that gallery height can be maintained at the same value for additional 24 h. The H-magadiite was affected by the solvation of intercalated octylamine as well recovered by filtering, washed with deionized water until Cl-free, and then dried in air at 40ЊC. as by the steric effect of solvated molecules.

Japanese Journal of Applied Physics, 2003

IEEE Transactions on Magnetics, 2009

Applied Physics Letters, 2005

We investigated the effect of humidity on the electrical transport properties of single-walled ca... more We investigated the effect of humidity on the electrical transport properties of single-walled carbon nanotube field effect transistors (SWNT-FETs). Water molecules are found to behave as electron donors to the nanotube: Current through the p-type carbon nanotube device is found to decrease under a modest humidity, and starts to increase as the humidity increases over 65%, which is believed to be due to the opening of electron channels. Through first principles calculations based on the density functional theory, we found that water molecules can donate electrons to the carbon nanotube. Moreover, a hydrogen-bonded water monolayer will be formed around the nanotube at fully covered conditions. We suggest that this result could provide a systematic understanding of the humidity effect on SWNT-FETs, which has been believed to be essential in the development of nanotube-based sensors.

Nanoscale, Jan 5, 2017

The recent development of strain sensor devices which can actively monitor human body motion has ... more The recent development of strain sensor devices which can actively monitor human body motion has attracted tremendous attention, for application in various wearable electronics and human-machine interfaces. In this study, as materials for strain sensor devices, we exploit the low-cost, carbon-based, 3-dimensional (3D) printable composite dough. The dough is prepared via a chemical method based on the formation of electrostatic assemblies between 1-dimensional, amine-functionalized, multi-walled carbon nanotubes and 2-dimensional graphene oxides. The resulting composite dough has an extremely high storage modulus, which allows a vertically-stackable, 3D printing process for fabricating strain sensor devices on various dense, porous and structured substrates. The device performance parameters, including gauge factor, hysteresis, linearity, and overshooting behavior are found to be adjustable by controlling the printing process parameters. The fabricated strain sensor devices demonstra...

Journal of Materials Chemistry, 2011

Synthesis of Cu/CuO core-shell Nanoparticles. Cu nanoparticles were synthesized via chemical redu... more Synthesis of Cu/CuO core-shell Nanoparticles. Cu nanoparticles were synthesized via chemical reduction of Cu ions in toluene (C 6 H 5 CH 3 , Aldrich, anhydrous 99.8%) under inert atmosphere. To prevent the interparticular agglomeration and surface oxidation, oleic acid (C 18 H 34 O 2 , Aldrich, 99%) was incorporated as a surface capping molecule and hydrazine (NH 2 NH 2 , Junsei, 98%) was used as a reducing agent. 16.6 g of Cu acetate (Cu(CO 2 CH 3) 2 , Aldrich, 98%), 10 g of oleic acid, and 16.6 g of hydrazine were added into a three-neck round-bottomed flask containing 100 mL of toluene. The flask was fitted with a reflux condenser and mechanical stirrer. The solution was purged with nitrogen for at least 30 min and then heated to 100 o C. Reaction was continued for 120 min and then cooled to room temperature. Then, the synthesized Cu nanoparticles were separated by centrifugation and washed with ethanol. The resulting Cu nanoparticles were well-dispersed in toluene, but not in aqueous medium. To endow the water-compatibility, we modified the surface of synthesized Cu nanoparticles by dipping Cu nanoparticles in methanol-based solution in which 6 wt% of carboxyl-terminated anionic polyelectrolyte, 16 wt% of mixture of polyoxylethylene oleylamine ether (Wako, M w = 1,000) and oxalic acid (C 2 H 2 O 4 , Aldrich, 99%) are dissolved. After reaction for 30 min under nitrogen atmosphere, the surface

Langmuir, 2011

With the aim of inkjet printing highly conductive and well-defined Cu features on plastic substra... more With the aim of inkjet printing highly conductive and well-defined Cu features on plastic substrates, aqueous based Cu ink is prepared for the first time using water-soluble Cu nanoparticles with a very thin surface oxide layer. Owing to the specific properties, high surface tension and low boiling point, of water, the aqueous based Cu ink endows a variety of advantages over conventional Cu inks based on organic solvents in printing narrow conductive patterns without irregular morphologies. It is demonstrated how the design of aqueous based ink affects the basic properties of printed conductive features such as surface morphology, microstructure, conductivity, and line width. The long-term stability of aqueous based Cu ink against oxidation is analyzed through an X-ray photoelectron spectroscopy (XPS) based investigation on the evolution of the surface oxide layer in the aqueous based ink.