• Nano
• /
• v.13 no.12
• /
• pp.1850142.1-1850142.9
• /
• 2018

Modified titanate nanotubes (TNT) were tested for their adsorption of methylene blue (MB) from water solutions. They were obtained from the $TiO_2$ nanopowder using a standard alkaline hydrothermal method but in the stage of acid washing, when the titanate flakes begin to roll into nanotubes, magnetite nanoparticles were added. The $Fe_3O_4$ magnetic nanoparticles with diameter of around 2 nm and 12 nm were used in the tests. Significantly stronger adsorption of MB was observed when smaller nanoparticles were used compared to using larger nanoparticles and compared to the case of unmodified nanotubes. It was shown that the increased adsorption of MB is associated with a more negative value of ${\zeta}$-potential for titanates modified by the ultra-small nanoparticles. In the adsorption experiment, pH 7 was selected. These results may prove to be of great importance in the case of potential applications corresponding to the use of such material for wastewater purification.

• Applied Science and Convergence Technology
• /
• v.24 no.4
• /
• pp.117-124
• /
• 2015

A direct growth method of graphene on insulating substrate without catalyst etching and transfer process was developed using Au/Ni/a-C catalyst system. During the growth process, behavior of the Au/Ni catalyst was investigated using EDX, XPS, SEM, and Raman spectroscopy. The Au/Ni catalyst layer was evaporated during growth process of graphene. The graphene film was composed mono-layer flakes. The transmittance of the graphene film was ~80.6%.

• Korean Journal of Materials Research
• /
• v.14 no.9
• /
• pp.664-669
• /
• 2004

Anodic aluminum oxide (AAO) with pores of various diameter, density, and thickness values was obtained through control of the anodization parameters including voltage, temperature, pore widening time, anodization time, etc. The pore diameter was controlled by a pore widening in an etchant, and alumina templates having stepped nano-channels were fabricated by repetition of anodization and pore widening processes. Stepped carbon nanotubes (CNTs) were then grown on the stepped AAO templates by pyrolysis of acetylene without using the catalyst. High-resolution transmission electron microscopy images revealed that CNTs have a multi-wall structure made of graphite flakes of several nm sizes. The current-voltage characteristic of the sloped and linear CNTs were also examined.

• Journal of the Microelectronics and Packaging Society
• /
• v.25 no.4
• /
• pp.95-99
• /
• 2018

High thermal conductivity films with electrically insulating properties have a great potential for the effective heat transfer as substrate and thermal interface materials in high density and high power electronic packages. There have been lots of studies to achieve high thermal conductivity composites using high thermal conductivity fillers such alumina, aluminum nitride, boron nitride, CNT and graphene, recently. Among them, hexagonal-boron nitride (h-BN) nano-sheet is a promising candidate for high thermal conductivity with electrically insulating filler material. This work presents an enhanced heat transfer properties of ceramic/polymer composite films using h-BN nano-sheets and PVA polymer resins. The h-BN nano-sheets were prepared by a mechanical exfoliation of h-BN flakes using organic media and subsequent ultrasonic treatment. High thermal conductivities over $2.8W/m{\cdot}K$ for transverse and $10W/m{\cdot}K$ for in-plane direction of the cast films were achieved for casted h-BN/PVA composite films. Further improvement of thermal conductivity up to $13.5W/m{\cdot}K$ at in-plane mode was achieved by applying uniaxial compression at the temperature above glass transition of PVA to enhance the alignment of the h-BN nano-sheets.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.9
• /
• pp.576-580
• /
• 2016

Single-layered transition metal dichalcogenides (TMDs) exhibit more interesting physical properties than those of bulk TMDs owing to the indirect to direct bandgap transition occurring due to quantum confinement. In this research, we demonstrate that layer-by-layer laser etching of molybdenum diselenide ($MoSe_2$) flakes could be controlled by varying the parameters employed in laser irradiation (time, intensity, interval, etc.). We observed a dramatic increase in the photoluminescence (PL) intensity (1.54 eV peak) after etching the samples, indicating that the removal of several layers of $MoSe_2$ led to a change from indirect to direct bandgap. The laser-etched $MoSe_2$ exhibited the single $MoSe_2$ Raman vibration modes at ${\sim}239.4cm^{-1}$ and ${\sim}295cm^{-1}$, associated to out-of-plane $A_{1g}$ and in-plane ${E^1}_{2g}$ Raman modes, respectively. These results indicate that controlling the number of $MoSe_2$ layers by laser etching method could be employed for optimizing the performance of nano-electronic devices.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.26 no.5
• /
• pp.175-180
• /
• 2016

ZnO nanoparticles were synthesized by aqueous preparation routes of a precipitation and a hydrothermal process. In the processes, the powders were formed by mixing aqueous solutions of Zn-nitrate hexahydrate ($Zn(NO_3)_2{\cdot}6H_2O$) with NaOH aqueous solution under controlled reaction conditions such as Zn precursor concentration, reaction pH and temperature. Single ZnO phase has been obtained under low Zn precursor concentration, high reaction pH and high temperature. The synthesized particles exhibited flakes (plates), multipods or rods morphologies and the crystallite sizes and shapes would be efficiently controllable by changing the processing parameters. The hydrothermal method showed advantageous features over the precipitation process, allowing the precipitates of single ZnO phase with higher crystallinity at relatively low temperatures below $100^{\circ}C$ under a wider pH range for the Zn precursor concentration of 0.1~1 M.

• Journal of Adhesion and Interface
• /
• v.20 no.3
• /
• pp.102-109
• /
• 2019

The material constitution of multi-layered thin film coated on the PET base film was analyzed using ATR FT-IR and pyro GC/MS combination. The cross section of the film was acquired by cracking the film after dipping in liquid nitrogen and was observed using optical microscope. Total thickness of the coated film was $70{\mu}m$ and three layers were observed. Since each layers were too thin to analyze directly except the surface layer, analyzable area of each layers were exposed by using a proper solvent and were investigated using ATR FT-IR and pyro GC/MS. Results shows that three layers were commonly consisted of urethane-acrylate copolymers. Also, inorganic and/or metal inclusions detected by XPS and SEM-EDAX were exhibited by nano size $SiO_2$ particles in layer(1) and aluminum flakes in layer(2).