Helmut Fischer Korea

Songpa gu, South Korea

Helmut Fischer Korea

Songpa gu, South Korea
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Choi S.-W.,Korea Institute of Science and Technology | Na H.G.,Inha University | Park S.,Helmut Fischer Korea | Hwang S.J.,Inha University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2017

Two different-sized SiOx nanowires and microtubes were grown from the surface of Si substrate, according to the distribution of Sn nanoparticles on the Si substrate. The numerous Sn nanoparticles obtained from pre-deposited SnO2 films on the tube play two roles simultaneously: the first is to act as a type of catalyst for promoting a rapid nucleation and growth, and the second is to decrease the melting point of the Si substrate. In order to maintain the phase equilibrium, changes at a morphological (nanowire, microtube, and split loops) and elemental compositional (aggregation and dispersion) level are involved in the Sn volume. © 2016 Elsevier B.V.

Park S.,Helmut Fischer Korea | Lee S.,Konkuk University | Jeong H.,Konkuk University | Jin C.,Konkuk University
Bulletin of the Korean Chemical Society | Year: 2016

Four different polymer-coated multi-walled carbon nanotubes (MWCNTs) were prepared under various catalyst-supporter conditions for examining the conductivity of the nanocomposites. The dimensions of the initial Al(OH)3 catalyst supporter, i.e., one of the final ternary catalysts, mainly determined the pristine MWCNT properties. The respective MWCNT-based composites with polycarbonate, high-density polyethylene, polypropylene, and low-density polyethylene generally exhibited remarkable catalyst supportdependent conductivity differences-approximately seven orders of magnitude, from 109.7 to 102.7. The degree of MWCNT dispersion is considered the key factor inducing the significant electrical differences. © 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Park S.,Helmut Fischer Korea | Kim Y.,Samsung | Kim M.,Helmut Fischer Korea | Lee D.,Konkuk University | And 2 more authors.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2015

Catalyst-assisted synthesis of multi-walled carbon nanotube (MWCNT) networks was successfully realized by controlling the catalyst particle size with and without post annealing. The sizes of ternary composite catalyst synthesized from spray pyrolysis method varied with different partial pressures and post-annealing. Various-sized MWCNT networks corresponding to individual catalyst sizes were produced through chemical vapor deposition technique. To investigate the dispersion of MWCNTs with respect to catalyst particle size, particle size analyses, scanning electron microscopy, and transmission electron microscopy were performed. In addition, the sieve shaker with 250 mesh were also used for evaluation of correlation between the MWCNTs networks and catalyst sizes. For electrical properties of the samples, MWCNT sheet resistance values were estimated with a four-point probe. These values were used to establish the optimal dispersion of MWCNTs needed to yield optimal carrier density and mobility. © 2015 Elsevier B.V. All rights reserved.

Jin C.,Konkuk University | Hwang S.J.,Inha University | Cho M.S.,Inha University | Choi S.-W.,Korea Institute of Science and Technology | And 5 more authors.
Nanotechnology | Year: 2016

SiOx structures with different diameters of a few hundreds of nanometers and/or a few micrometers are prepared using applied thermal evaporation. Subsequently, Sn quantum dot-based SiOx architectures are synthesized via the continuous steps of the carbothermal reduction of SnO2, substitution of Sn4+ for In3+, thermal oxidation of Si, Sn sublimation, interfacial reaction, and diffusion reaction consistent with corresponding phase equilibriums. Several crystalline and spherical-shaped Sn quantum dots with diameters between 2 and 7 nm are observed in the amorphous SiOx structures. The morphological evolution, including hollow Sn (or SnOx) sphere and wire-like, worm-like, tube-like, and flower-like SiOx, occurs stepwise on the Si substrate upon increasing the given process energies. The optical characteristics based on confocal measurements reveal the as-synthesized SiOx structures, irrespective of whether crystallinity is formed, which all have visible-range emissions originating from the numerous different-sized and -shaped Sn quantum dots permeating into the SiOx matrix. In addition, photoluminescence emissions ranging between ultraviolet and red regions are in agreement with confocal measurements. The origins of the morphology- and luminescence-controlled amorphous SiOx with Sn quantum dots are also discussed. © 2016 IOP Publishing Ltd.

Na H.G.,Hanyang University | Choi S.-W.,Korea Institute of Science and Technology | Park S.,Helmut Fischer Korea | Hwang S.J.,Inha University | And 5 more authors.
Crystal Growth and Design | Year: 2016

In contrast with conventional thermal evaporation-based semiconducting oxide growth methods, gourd-like SiOx nanotubes (NTs) grown from Si substrates were achieved with incorporated Sn-embedded structures through the precontaminated SnO2 film surroundings. Interestingly, when Sn aggregations assembled as Sn nanoparticles were formed on the surface of the Si substrate, single gourd-like SiOx NTs were grown from the upper local region of the ternary alloy (Si-Sn-O) sphere, maintaining a one-to-one correspondent relationship between the ternary spheres and the Sn-embedded SiOx NTs. Both interfacial reaction-controlled and diffusion-controlled systems occurred stepwise at the smooth and rough surfaces, respectively. In addition, the elemental compositions and sizes of the final Sn-embedded SiOx NTs were influenced by the Sn concentration of the SnO2 film, the rate of In substitution by Sn in the supporting material In2O3, and the degree of carbothermal reduction of additional graphite powders. © 2016 American Chemical Society.

Park S.,Helmut Fischer Korea | Na H.G.,Hanyang University | Choi S.-W.,Korea Institute of Science and Technology | Jin C.,Konkuk University
Synthetic Metals | Year: 2016

Impregnation-dependent nanocomposites, consisting of multi-walled carbon nanotube (MWCNT) and low-density polyethylene (LDPE), were successfully produced by controlling the catalyst-supporter size during catalyst fabrication. The MWCNTs fabricated by the impregnation method with different dimensionalities such as pore density and size were compared with MWCNTs fabricated by the spray drying technique. After mixing MWCNTs with LDPE using an extruder, the individual composite constituents showed different physical and electrical properties related to dispersion and sheet resistance, depending on catalyst-supporter dimensionality. For more detailed dispersion control of the extruded composite, scanning and transmission electron microscopy and sheet-resistance measurement were performed. Furthermore, the electrical properties of MWCNT composites with poly methyl methacrylate (PMMA) instead of LDPE were investigated for comparison. The fabrication of MWCNT composites using the impregnation technique with size-controllable catalyst supporters is regarded as a good synthetic method for realizing optimal MWCNT-based electronic devices. © 2016 Elsevier B.V. All rights reserved.

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