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Publications (51)
Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs) have attracted extensive interest in various fields owing to their unique electronic properties. However, studies on their transport properties and the modulation of these properties based on their band structure are limited. Herein, we studied the transport phenomena in 2D meta...
For the successful commercialization of Bi2Te3-based thermoelectric generator (TEG) devices, not only highly efficient TE materials, but also reliable bonding materials with high thermal stability are essential. In this study, we investigated the application of Cu nanoparticle paste (CNP) bonding for increasing the operating temperature of Bi2Te3-b...
A soft and stable substrate is an essential component for realizing flexible electronics and displays. We fabricated flexible substrate films by compositing iron oxide nanoparticle-conjugated graphite platelets (mGPs) with polyimide (PI). We controlled the microstructure of the composite film by aligning the mGPs with a low magnetic field in the ve...
We investigated the thermoelectric properties of composite films that consist of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and single-walled carbon nanotubes (SWCNTs). Thin films with 5−10 μm thickness of PEDOT:PSS/SWCNT and PEDOT:PSS/acid-treated SWCNT (AC-SWCNT) were prepared by varying the CNT content to determine thei...
We suggest a way to control the crystal orientation of LiFePO4 using a magnetic field to obtain an advantageous structure for lithium ion conduction. We examined the magnetic properties of LiFePO4 such as magnetism and magnetic susceptibility, which are closely related to the crystal rotation in an external magnetic field, and considered how to use...
We suggested a defect system consisting of Te- and Ag-related defects in n-type Bi2(Te,Se)3. We prepared the Terich
Bi2Te2.88Se0.15 compound, which is expected to have Te antisite defects, via a conventional pulverization
process. We devised a one-pot chemical process in which Ag nanoparticles were synthesized and instantly deposited
onto the Bi2Te...
Enhancement in thermoelectric performance of n-type Bi2(Te,Se)3 was accomplished by forming the dual defect system composed of Te- and Ag-related defects. The Te-rich Bi2(Te,Se)3+y, which should have antisite defects generated by the excessive Te, was prepared via a conventional melting process. We devised the one-pot process, in which Ag nanoparti...
We provided a Bi2Te3-polypyrrole hybrid material, in which energy band junction and phonon scattering effects should appear at the interface of the two components. The hybrid material exhibited increases in electrical resistivity and the Seebeck coefficient due the energy band junction, thus retaining the power factor without loss, whereas showing...
We hybridized n-type Bi2Te3 with an inexpensive and abundantly available conducting polymer, polypyrrole, to obtain a bulk-structured hybrid material in which the interfacial energy band and the phonon scattering effects should occur at the interface of the two components. The obtained hybrid material inevitably exhibited a lower electrical conduct...
Carbon-based fillers for thermal interface materials (TIMs) are attractive due to their advantages such as high thermal conductivity, low thermal expansion, mechanical strength, flexibility, and low weight. In this work, we report a 330% enhancement of the through-plane thermal conductivity (kth) of a graphite-polymer composite TIM film by vertical...
We report significant enhancement in thermoelectric performance of n-type Bi-2(Te,Se)(3) prepared via conventional melting process. We deposited chemically synthesized Ag nanoparticles onto Te-rich Bi-2(Te,Se)(3) and sintered the resulting substance to obtain a bulk product. The Ag nanoparticles and excessive Te elements should be converted to inte...
We report the hyperthermia properties of Fe3O4–Au hybrid nanoparticles (HNPs) under a biocompatible alternating magnetic field (AMF) of 1.5 kA m⁻¹ and 200 kHz. The HNPs were prepared by growing Au nanoparticles (AuNPs) with an average diameter of 3 nm on the surface of Fe3O4 magnetic nanoparticles (MNPs) with an average diameter of 10 nm. The struc...
A polycrystalline WSe2 nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-plane direction with covalent bonds rather than along the through-plane direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structur...
We studied a polycrystalline p-type WSe2 semiconductor for thermoelectric applications. The polycrystalline WSe2 nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological...
Chemical reaction processes for thermoelectric nanomaterials have received a lot of attention because of subsequent small and uniform nanostructures, causing a remarkable reduction in thermal conductivity; however, they typically showed low electrical properties possibly due to contaminations by chemicals resulting in low ZT. We devised a new chemi...
Various chemical reaction processes have been adopted to synthesize Bi2Te3 thermoelectric nanomaterials for achieving remarkably low thermal conductivities, but chemical contaminations were usually pointed out as flaws, severely deteriorating electrical conductivities. We devised a novel water-based chemical reaction process for a Bi2Te2.7Se0.3 nan...
We synthesized ternary n-type bismuth tellurium selenide nanomaterials for thermoelectric applications via a water-based chemical reaction under an atmospheric environment. In this work, bismuth nitrate was employed as a bismuth precursor and was hydrolyzed to form bismuth hydroxide in an aqueous solution. Ascorbic acid was used to dissolve the bis...
We synthesized ternary n-type bismuth tellurium selenide nanomaterials for thermoelectric applications via a water-based chemical reaction under an atmospheric environment. In this work, bismuth nitrate was employed as a bismuth precursor and was hydrolyzed to form bismuth hydroxide in an aqueous solution. Ascorbic acid was used to dissolve the bis...
A tellurium evaporation annealing method has been investigated to control the carrier concentration of sintered (Bi,Sb)2Te3 compounds. Hot-pressed (Bi,Sb)2Te3 bulk alloys and tellurium powders located in an evacuated ampoule, were heated to 673 K and held for 3, 12 and 48 h. The crystal structure and chemical composition in the annealed specimens w...
A solution-based process was developed for the preparation of a CuInTe2 material that can be used as an absorber in thin-film photovoltaics. We performed a solvothermal synthesis under specific processing conditions to generate the CuInTe2 material. The resulting product showed different diffraction patterns and morphology depending on the reaction...
Single crystalline Bi-Te thermoelectric
materials have a rhombohedral structure with van der Waals bonding along c-axis direction. This structure gives intrinsic anisotropy in thermoelectric
properties like electrical resistivity,
thermal conductivity, Seebeck coefficient, as well as electron/hall mobility. Recent research works report that nano st...
A binary BiTe nanocompound for thermoelectric applications was prepared via a water-based chemical reaction under atmospheric conditions. We attempted to increase the carrier mobility of the nanocompound by adopting a post-thermal treatment consisting of calcination and reduction at different temperatures. We also tried to control the carrier densi...
The synthesized n-type perylene derivative, N,N'-bis-(4-bromophenyl)-1,6,7,12-tetrakis(4-n-butoxy-phenoxy)-3,4,9,10-perylene tetracarboxdiimide (PIBr), was applied as an additive to polymer solar cells (PSCs) with P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl C61-butyric acid methyl ester] blend films. Without post thermal annealing, a considera...
We investigated the thermoelectric properties of sintered Bi0.5Sb1.5Te3 alloys containing grains for their alignment, sizes and shapes. The figure of merit can be improved as the result of lower resistivity by increasing the alignment, which is realized by using the spark plasma sintering method and a strong magnetic field. In addition, making the...
Bismuth telluride nanoparticles for thermoelectric applications were successfully prepared via a water-based chemical reaction. In this process, we used both a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursor (Bi(NO3)3) in water and to favor the reaction with the reduced sour...
A bismuth tellurium selenide (Bi2TeySe3−y) nanocompound for thermoelectric applications was successfully prepared via a water-based chemical reaction in an atmospheric environment. The compound was less that ca. 100nm in size, with a crystalline structure corresponding to the rhombohedral Bi2Te2.7Se0.3. We sintered the compound via a spark plasma s...
We simultaneously investigated the effects of nanostructure and crystal alignment on the thermoelectric performance of polycrystalline Bi0.5Sb1.5Te3. An appropriate experimental procedure was devised for a sequential process of slip-casting under a 6T magnetic field for c-axis alignment and the use of a spark plasma sinter machine for sintering. Fl...
With a view to experimental demonstration for an improved thermoelectric performance, a slip casting method under high magnetic field for uni-directionally aligned crystals has been investigated. The sintered body of Bi2Te3 powder, its size between 300 and 500nm, green-bodied under 6T magnetic field showed a 33% variation in the fraction of the dir...
Bismuth tellurium selenide (Bi2TeySe3−y) nanoparticles for thermoelectric applications are successfully prepared via a water-based chemical reaction under atmospheric conditions. The nanostructured compound is prepared using a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursor...
Antimony telluride (Sb2Te3) nanoparticles for thermoelectric applications were successfully prepared via a water-based chemical reaction under atmospheric conditions. In this process, we tried to prepare the nanostructured compound by employing both a complexing agent (l-tartaric acid) and a reducing agent (NaBH4) to stabilize the Sb precursor (SbC...
The influence of the starting powders’ morphology on the thermoelectric anisotropy of Bi–Te-based thermoelectric materials that are fabricated by spark plasma sintering has been investigated. Starting powders with three types of morphologies are prepared through a chemical reaction method (nano-sized particles with a spherical shape), a conventiona...
This work reports on the preparation of modified TiO2 electrodes, which could be applied to the photoanodes of dye-sensitized solar cells (DSSCs). TiO2 layers were formed on fluorine-doped tin oxide glasses via doctor-blade method followed by heat treatment. Then, the various metal hydroxides were individually incorporated onto the TiO2 layers via...
Three n-type polymers, Ppe01, Ppe02, andPpe03, containing both perylene moieties and fluorine atoms were synthesized. The synthesiszed polymeric perylene derivatives with good compatibility for solution processes were chosen as new acceptor candidates for substitution of C60 derivatives in poly(3-hexylthiophene)-based organic photovoltaic applicati...
This work reports on the preparation of modified TiO2 electrodes, which could be applied to the photoanodes in a dye-sensitized solar cells (DSSCs). TiO2 layer was formed on a FTO (fluorine-doped tin oxide) coated glass via doctor-blade method and post heat treatment. Then, the various metal hydroxides and metal oxides were selectively deposited on...
Three emitting materials containing a biphenyl core connected at both ends with phenoxazine or anthracene groups, 10-(3-(10H-phenoxazin-10-yl)-6-phenylphenanthridin-8-yl)-10H-phenoxazine (DPoPP), 8-(anthracen-10-yl)-3-(anthracen-9-yl)-6-phenylphenanthridine (DAnPP), and 2-(anthracen-10-yl)-7-(anthracen-9-yl)-4,5,9,10-tetrahydropyrene (DAnTP) were s...
We reported the development of new nanoscale drug carriers, chitosan-based nanoparticles (CNPs) that can be used for photodynamic therapy. These carriers could encapsulate a photosensitizer, protophorphyrin IX (PpIX), and deliver it to tumor tissue. We already reported that CNPs presented the enhanced tumor target specificity in cancer therapy and...
We have developed photocatalytic TiO2 nanofibers for the treatment of organic pollutants by using electrospinning method. We found that the optimized electrospinning conditions (electric field and flow rate) were 0.9 kV cm(-1) and 50 microL min(-1). After annealing at 550 degrees C for 30 min, we fabricated TiO2 nanofibers (average 236 nm thick) wi...
Nanoscale materials can be rationally designed to exhibit significantly changed physical, chemical, and biological properties because of the extremely small dimensions. Therefore, atactic poly(vinyl alcohol) (a-PVA) nanowebs by an electrospinning technique have very high water solubility because of their nanoscale in comparison with microscale mate...
A dopant, 4,4′-bis(dimethyl[4-(2-phenyl-buta-1,3-dienyl)phenyl]amine) biphenyl (BPAB), was synthesized, and single layered polymer light emitting diode (PLED)s, ITO/Host:Dopant/Al, were fabricated with blends of poly(vinyl carbazole) (PVK) as host and BPAB as dopant. The electroluminescence (EL) was observed in doped PLEDs. From the EL and photolum...
Poly(1,1′-biphenyl-4,4′-ylene vinylene-alt-2,5-bis(2-ethylhexyl)-1,4-phenylene vinylene] [poly(BPV-alt-BEHPV)] as a polymeric dopant, was synthesized by Honer-Emmons condensation from corresponding dialdehyde and diphosphonate monomers. Synthesized alternating polymer was used to fabricate single layer (ITO/Host:Dopant/Al) PLEDs with poly(vinyl car...
Electroluminescent properties of polymer light-emitting diode (PLED)s fabricated from heterocyclic conjugated random copolymers, poly(PZV-ran-CZV), containing (N-2-ethylhexyl)-3,6-phenothiazinylene vinylene (PZV), (N-2-ethylhexyl)-3,6-carbazolylene vinylene (CZV) and phenylene vinylene (PV) unit as a light emitting layer were investigated. PLEDs ma...
In this work, silver nanoparticles were embedded in electrospun organic/inorganic composite nanofibers consisting of PAN and TiO 2 through photocatalytic reduction of the silver ions in silver nitrate solutions under UV irradiation. The morphology and diameter of PAN/TiO 2 composite nanofibers could be controlled by varying the initial contents of...
Back Cover: The picture on the cover shows the schematic representation of a simple preparation method for organic‐inorganic composite nanofibers containing functional noble metal nanoparticles. TEM images shows that the surface of TiO 2 in the composite nanofibers has been decorated with Ag nanoparticles (diameter ca. 2 nm) with the type of polka...
A level measuring system has been investigated to work with the electromagnetic continuous casting of steel billet, based on the principle of electromagnetic induction. The basic idea of the development is the distinction of the magnetic field measured in the mold into the effect of the applied one and the effect of the level variation. Several can...
The electromagnetic continuous casting technology has been investigated in commercial scale casting experiments at a billet caster of POSCO works. A set of facility composed of coil & mold with a specially devised molten metal level meter, and software for casting monitoring were well suited to No. 2 billet caster of POSCO. The devised EMC facility...
In order to develop the high frequency electromagnetic continuous casting technology for applying to steel, numerical analysis of the magnetic field and casting experiments using various parameters have been conducted. The method of using cold inserts was well established to lead to a reliable numerical model. According to this numerical model, it...
The objective of this study is to improve the surface quality of the billet by applying high-frequency magnetic field electromagnetic casting technology to the continuous casting of steel. In this study, the effect of the mold shape on the steel billet surface quality was examined by a continuous casting experiment. It also researched the effects o...
A three dimensional model for simulating the semi-continuous solidification process accompanying mass-transfer in electromagnetic casting (EMC) of aluminum alloys was described in this paper. The electromagnetic skin-effect and the Joule heating were incorporated into the computation equation by a proposed formula. Numerical and experimental result...
In order to increase the casting speed of semi-continuous casting of aluminum billet, a mold with slits and external cooling water channels was designed. This cooling system can supply enough cooling strength and keep the cooling rate readily. By imposing a high frequency magnetic field, the surface quality and microstructure of the billets are imp...
The vortex formation in draining the melt in ladle can be suppressed by the reduction of the tangential flow velocity of the melt. Two magnetic devices were designed in order to reduce the tangential flow velocity and tested with wood metal melt. One consists of 4 permanent magnets (PM device) and the other consists of an electromagnet (EM device)....
