• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.357-363
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• 2019

We investigated a synthesis yield and diameter distribution of single-walled carbon nanotubes (SWNTs) with respect to the growth position in a horizontal chemical vapor deposition (CVD) chamber. Thin films and line-patterned Fe films (0.1 nm thickness) were prepared onto ST-cut quartz substrates as catalyst to compare the growth behavior. The line-patterned samples showed higher growth density and parallel alignment than those of the thin film catalyst samples. In addition, line density of the aligned SWNTs at central region of the chamber was 7.7 tubes/㎛ and increased to 13.9 tubes/㎛ at rear region of the CVD chamber. We expect that the enhanced amount of thermally decomposed feedstock gas may contribute to the growth yield enhancement at the rear region. In addition, the lamina flow in the chamber also contribute to the perfect alignment of the SWNTs based on the value of gas velocity, Reynold number, and Knudsen coefficient we employed.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.138-143
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• 2011

To investigate the electromagnetic interference shielding efficiency (EMI SE) property based on heat treatment effects of carbon fibers in various temperatures, the polyacrilonitrle-based carbon fibers were prepared by electrospinning method and treated at 1073, 1323, 1873 and 2573 K. The surface morphology of carbon fibers was investigated by using FE-SEM and the carbon crystallization was studied by Raman spectroscopy based on effects of reaction temperatures. The electrical conductivity was obtained by measuring the surface resistance with four probe method on carbon crystallization. The permittivity, permeability and EMI SE were investigated by using S-parameter in the range of 800~4500 MHz. In case of carbon fibers treated at 2573 K, the improved carbon crystallization was confirmed by Raman spectrum and the enhanced electrical conductivity showing 54.7 S/cm was also observed. The permittivity was dramatically improved by factor of 4 based on effect of high reaction temperature. Eventually, the highly improved EMI SE value was obtained showing around 41.7 dB.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.441-442
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• 2012

SnNb2O6 nanoplates were prepared by a solvothermal synthesis with water and ethanol mixed solvent. For improvement of their properties, as-prepared SnNb2O6 nanoplates also were calcined. The prepared powder was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Transmission electron microscope (TEM), UV-vis spectroscopy, Raman spectrometer, Brunauer-Emmett-Teller (BET). The calcined nanoplates have a smaller surface area than the as-prepared nanoplates have. Nevertheless, in the case of the optical absorption properties, the calcined nanoplates could absorb more photon energy, due to their smaller band gaps. The Raman analysis revealed that the Nb-O bond length in the calcined nanoplates was longer than that in the as-prepared nanoplate. The higher optical absorption capability of the calcined nanoplates was attributed to the local structure variation within them. Furthermore the high crystallinity of the calcined nanoplates is effective in improving the generation of charge carriers. So, It was found that the calcined nanoplates exhibited superior photocatalytic activity for the evolution of H2 from an aqueous methanol solution than the as-prepared nanoplates under UV and visible irradiation. Therefore, the enhanced photocatalytic activity of the calcined nanoplate powder for H2 evolution was mainly attributed to its high crystallinity and improved optical absorption property resulting from the variation of the crystal structure.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1737-1739
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• 2004

Diamond-like carbon (DLC) films were prepared with RF-PECVD (Plasma Enhanced Chemical Vapor Deposition) method on coming glass and silicon substrates using methane ($CH_4$) and hydrogen ($H_2$) gases. We examined the effects of $CH_4$ to $H_2$ ratios on tribological and optical properties of the DLC films. The structure and surface morphology of the films were examined using Raman spectroscopy and atomic force microscopy (AFM). The hardness of the DLC film was measured with nano-indentor. The optical properties of DLC thin film were investigated by UV/VIS spectrometer and ellipsometry. And also, solar cells were fabricated using DLC as antireflection coating before and after coating DLC on silicon substrate and compared the efficiency.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.294-298
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• 2015

Blocking layers with nano carbon blacks (NCBs) were prepared by adding 0.0 ~ 0.5 wt% NCBs to the $TiO_2$ blocking layer. Then, dye sensitized solar cells (DSSCs) were fabricated with a $0.45cm^2$ active area. TEM and micro-Raman spectroscopy were used to characterize the microstructure and phases of the NCBs, respectively. Optical microscopy and AFM were used to analyze the microstructure of the $TiO_2$ blocking layer with NCBs. UV-VIS-NIS spectroscopy was used to determine the band gap of the $TiO_2$ blocking layer with NCBs. A solar simulator and potentiostat were used to determine the photovoltaic properties and impedance of DSSCs with NCBs. The energy conversion efficiency (ECE) increased from 3.53 to 6.20 % when the NCB content increased from 0.0 to 0.3 wt%. This indicates that the effective surface area and electron mobility increased in the $TiO_2$ blocking layer with NCBs. However, the ECE decreased when the NCB content was increased to over 0.4 wt%. This change occurred because the effective electron transport area decreased with the addition of excessive NCBs to the $TiO_2$ blocking layer. The results of this study suggest that the ECE of DSSCs can be enhanced by adding the appropriate amount of NCBs to the $TiO_2$ blocking layer.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.504-507
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• 2012

Synthesis of RGO (reduced graphene oxide)-CdS composite material was performed through CBD (chemical bath deposition) method in which graphene oxide served as the support and Cadmium Sulfate Hydrate as the starting material. Graphene-based semiconductor photocatalysts have attracted extensive attention due to their usefulness for environmental and energy applications. The band gap (2.4 eV) of CdS corresponds well with the spectrum of sunlight because the crystalline phase, size, morphology, specic surface area and defects, etc., of CdS can affect its photocatalytic activity. The specific surface structure (morphology) of the photocatalyst can be effective for the suppression of recombination between photogenerated electrons and holes. Graphene (GN) has unique properties such as a high value of Young's modulus, large theoretical specific surface area, excellent thermal conductivity, high mobility of charge carriers, and good optical transmittance. These excellent properties make GN an ideal building block in nanocomposites. It can act as an excellent electron-acceptor/transport material. Therefore, the morphology, structural characterization and crystal structure were observed using various analytical tools, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. From this analysis, it is shown that CdS particles were well dispersed uniformly in the RGO sheet. Furthermore, the photocatalytic property of the resulting RGO-CdS composite is also discussed in relation to environmental applications such as the photocatalytic degradation of pollutants. It was found that the prepared RGO-CdS nanocomposites exhibited enhanced photocatalytic activity as compared with that of CdS nanoparticles. Therefore, better efficiency of photodegradation was found for water purification applications using RGO-CdS composite.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.351-355
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• 2014

Graphite electrodes are used for secondary batteries, fuel cells, and super capacitors. Research is underway to increased the reaction area of graphite electrodes used carbon nanotube (CNT) and porous carbon. CNT is limited to device utilization in order to used a metal catalyst by lack of surface area to improve. In contrast carbon nanowall (CNW) is chemically very stable. So this paper, microwave plasma enhanced chemical vapor deposition (PECVD) system was used to grow carbon nanowall (CNW) on Si substrate with methane ($CH_4$) and hydrogen ($H_2$) gases. To find the growth properties of CNW according to the reaction gas ratio, we have changed the methane to hydrogen gas ratios (4:1, 2:1, 1:2, and 1:4). The vertical and surficial conditions of the grown CNW according to the gas ratios were characterized by a field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy measurements showed structure variations.

• Applied Chemistry for Engineering
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• v.32 no.2
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• pp.143-148
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• 2021

A thermally conductive 200 ㎛ thick polyimide-based film was made from a polyamic acid (PAA) precursor containing graphene prepared from graphite rod using an electrostatic discharge method in order to improve the thermal conductivity and expand the applicability of polyimide (PI) film. Properties of graphene produced by electrostatic discharge were measured by Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). As a result of Raman spectrum and XPS analyses of as-prepared graphene, the ID/IG ratio was 0.138 and C/O value was 24.91 which are excellent structural and surface chemical properties. Moreover, thermal conductivities of polyimide films increased exponentially according to graphene contents but when the graphene content exceeded 40%, the polyimide film could not maintain its shape. The thermal conductivity of carbonized PI film made from PAA containing 40 wt% of graphene was 51 W/mK which is greatly enhanced from the pristine carbonized PI film (1.9 W/mK). This result could be originated from superior properties of graphene prepared from the electrostatic discharge method.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.393-393
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• 2012

Optically active nanostructures such as subwavelength moth-eye antireflective structures or surface enhanced Raman spectroscopy (SERS) active structures have been demonstrated to provide the effective suppression of unwanted reflections as in subwavelength structure (SWS) or effective enhancement of selective signals as in SERS. While various nanopatterning techniques such as photolithography, electron-beam lithography, wafer level nanoimprinting lithography, and interference lithography can be employed to fabricate these nanostructures, roll-to-roll (R2R) nanoimprinting is gaining interests due to its low cost, continuous, and scalable process. R2R nanoimprinting requires a master to produce a stamp that can be wrapped around a quartz roller for repeated nanoimprinting process. Among many possibilities, two different types of mask can be employed to fabricate optically active nanostructures. One is self-assembled Au nanoparticles on Si substrate by depositing Au film with sputtering followed by annealing process. The other is monolayer silica particles dissolved in ethanol spread on the wafer by spin-coating method. The process is optimized by considering the density of Au and silica nano particles, depth and shape of the patterns. The depth of the pattern can be controlled with dry etch process using reactive ion etching (RIE) with the mixture of SF6 and CHF3. The resultant nanostructures are characterized for their reflectance using UV-Vis-NIR spectrophotometer (Agilent technology, Cary 5000) and for surface morphology using scanning electron microscope (SEM, JEOL JSM-7100F). Once optimized, these optically active nanostructures can be used to replicate with roll-to-roll process or soft lithography for various applications including displays, solar cells, and biosensors.

• Journal of the Korean Vacuum Society
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• v.12 no.1
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• pp.35-39
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• 2003

Using RF plasma enhanced chemical vapor deposition, amorphous carbon films were grown in pure methane plasma. Field electron emission of these films were examined at a function of deposition temperature. It was found that the electron emission current of the sample prepared at deposition temperature above $600^{\circ}C$ was considerably improved. The film grown at deposition temperature of $800^{\circ}C$ had the best threshold field of 8 V/$\mu\textrm{m}$ in this experiment. According to the results of Raman spectroscopy. growth of graphite crystallites was promoted with higher deposition temperatures. Moreover the surface morphology was abruptly changed at deposition temperature above $600^{\circ}C$. We discuss the field electron emission characteristics of amorphous carbon films with regard to the structural feature and surface morphology.