Heon Ham

Fabrication of graphene layers from multiwalled carbon nanotubes using high dc pulse

Graphene layers are fabricated from multiwalled carbon nanotubes (MWCNTs) with a high direct current pulse through a pulsed current sintering process. We confirm the transformation of the structure from MWCNTs to graphene layers. Graphene layers are analyzed by field emission scanning electron microscopy, high resolution transmission electron microscopy, high resolution Raman, and x-ray diffraction.

Evidence of Ostwald ripening during evolution of micro-scale solid carbon spheres

Ostwald ripening is an evolutionary mechanism that results in micro-scale carbon spheres from nano-scale spheres. Vapor-phase carbon elements from small carbon nanoparticles are transported to the surface of submicron-scale carbon spheres, eventually leading to their evolution to micro-scale spheres via well-known growth mechanisms, including the layer-by-layer, island, and mixed growth modes. The results obtained from this work will pave the way to the disclosure of the evolutionary mechanism of micro-scale carbon spheres and open a new avenue for practical applications.

Fabrication of single-phase titanium carbide layers from MWCNTs using high DC pulse

Single-phase layered titanium carbide (TiC) was successfully synthesized by reacting carbon nanotubes (CNTs) and titanium dioxide (TiO2) under a high direct current (DC) pulse. Single-phase TiC layer fabrication is confirmed as the transformation of multi-layered graphene from MWCNTs. Therefore its thickness and width is almost identical to those of transformed graphene layers. This is the first report on the formation of single-phase layered nano-TiC. Scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM) were used for the characteristic analysis of single-phase layered TiC structures.

Synthesis of graphene nano-sheet without catalysts and substrates using fullerene and spark plasma sintering process

*Korea National University of Transportation, Civil. Environmental and Transportation Engineering, Chungju 380-702, Korea**Department of Textile Convergence of Biotechnology & Nanotechnology, Korea Institute of Industrial Technology, Ansan 426-910, Korea***National Nanotechnology Policy Center, Korea Institute of Science and Technology Information (KISTI), Seoul 130-741, Korea****Department of Bio & Environmental Engineering, Semyung University, Jecheon 390-711, Korea*****Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea

Phosphate removing by graphene oxide in aqueous solution

Phosphate has been removed in waste water by chemically synthesized graphene oxide. Removing efficiency of phosphate was investigated using phosphate dispersion aqueous solution, and 70 % of phosphate was removed in phosphate dispersion solution by chemically synthesized graphene oxide solution. Removing efficiency of phosphate was increased from 70 % to 80 % with assistant of iron nano-particle in chemically synthesized graphene oxide solution. Phosphate removing capacity was up to 89.37 mg/g at initial phosphate concentration of 100 mg/l and temperature of 303 K. The Freundlich was applied to describe the equilibrium isotherms and the isotherm constants were determined.

Different morphologies of three dimensional ZnO structures synthesized by thermal evaporation method without a catalyst

ZnO with different morphologies can be used various application depending on their shapes. Different morphologies of ZnO structures were synthesized by a catalysis-free thermal evaporation process. Their morphologies were dependent on the distance from the source to substrate on the same processing condition; in the result were products morphologies of the hollow, cage and star. Their shapes and crystalinity were evaluated by SEM and XRD, respectively. This work demonstrates what kind of growth factors would be involved in the final structure morphologies.

Electrical Properties of Novel Polyolefin Based Thermoplastic Elastomer and Graphene Nanocomposites

Numerous efforts to prepare useful graphene-based nanocomposites have been made and important improvements achieved. In our studies, novel structured polyolefin-based thermoplastic elastomer, poly(ethylene-ter-1-hexene-ter-divinylbenzene) (PEHV) was designed and synthesized. And high quality graphene was manufactured via the exfoliation of graphite. PEHV/graphene nanocomposites were fabricated using solution casting method as the amount of graphene added. The morphologies of nanocomposites were observed using scanning electron microscopy. And density, mechanical properties and electrical properties were also measured. Electrical properties and mechanical properties were improved with the increase of graphene added in nanocomposites. It is expected that PEHV/graphene nanocomposites could be applied to lightweight EMI shielding materials.

High-quality ZnO nanowire arrays directly synthesized from Zn vapor deposition without catalyst

Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on GaN/sapphire and Si substrate from Zn vapor deposition without catalysts. Experimental results showed that the number density, diameter, crystallinity and degree of the alignment of ZnO NWs depended strongly on both the substrate position and kind of the substrates used for the growth. The photoluminescence (PL) characteristics of the grown ZnO NW arrays exhibit a strong and sharp ultraviolet (UV) emission at 379 nm and a broad weak emission in the visible range, indicating that the obtained ZnO NWs have a high crystal quality with excellent optical properties. The as-grown ZnO NWs were characterized by using scanning electron microscopy (SEM), high resolution transmission electronic microscopy (HR-TEM), and X-ray diffraction (XRD).

Fabrication of single-phase tungsten carbide laminae from multi- walled carbon nanotubes using high direct current pulse

Single-phase tungsten carbide (WC) laminae were fabricated by reacting of multi-walled carbon nanotubes (MWCNTs) and tungsten trioxide using high direct current pulses. We confirmed that single-phase WC laminae are transformed from unzipped MWCNTs, and that they have a graphene layer structure. Therefore their thicknesses and widths are almost identical with those of transformed graphene layers from MWCNTs. A variety of characterizing techniques, such as a field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, has been used for the investigation of the characteristics of single-phase WC laminae.