• Journal of Powder Materials
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• v.16 no.4
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• pp.243-248
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• 2009

Carbon-coated Cu nanopowders with core/shell structure have been successfully fabricated by pulsed wire evaporation (PWE) method, in which a mixed gas of Ar/$CH_4$ (10 vol.%) was used as an ambient gas. The characterization of the samples was carried out using x-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM). It was found that the nanoparticles show a spherical morphology with the size ranging of 10-40 nm and are covered with graphite layers of 2-4 nm. When oxygen-passivated Cu nanopowders were annealed under flowing argon gas (600 and 800$^{\circ}C$), the crystallinity of $Cu_2O$ phase and the particle size gradually increased. On the other hand, carbon-coated Cu nanopowders remained similar to as-prepared case with no additional oxide or carbide phases even after the annealing, indicating that the metal nanoparticles are well protected by the carbon-coating layers.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.449-455
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• 2010

To enhance the efficiency of dye sensitized solar cells, we proposed crystalline anatase-$TiO_{2}$ by using a low temperature process ($150^{\circ}C{\sim}250^{\circ}C$). We successfully fabricated 30 nm-$TiO_{2}$ at a fixed atomic layer deposition condition of 1.0 sec of TDMAT pulse, 20 sec of TDMAT purge, 0.5 sec of H$_{2}$O pulse, and 20 sec of H$_{2}$O purge. In order to examine the microstructure, phase, and band-gap of the TiO$_{2}$ respectively, we employed a Nano-Spec, transmission electron microscope, high resolution XRD, Auger electron spectroscopy, scanning probe microscope, and UV-VIS-NIR. We were able to fabricate a crystalline anatase-phase of 30 nm-TiO$_{2}$ successfully at temperatures above $180^{\circ}C$. Our results showed that our proposed low temperature ALD process (below $200^{\circ}C$) might be applicable to glass and flexible polymer substrates.

• Journal of Sensor Science and Technology
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• v.28 no.4
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• pp.266-269
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• 2019

In this study, $Ag_2Se$ nanoparticles were synthesized by employing the colloidal method. The synthesized $Ag_2Se$ nanocrystals were spherical in shape with a diameter of approximately 4 nm and had high crystallinity. These attributes of $Ag_2Se$ nanocrystals were determined through images obtained from a high resolution transmission electron microscope. Thin films comprising the synthesized $Ag_2Se$ nanoparticles had an optical band gap of 1.5 eV. Furthermore, fabricated NIR sensors comprising $Ag_2Se$ nanoparticles exhibited a high detectivity of $5.5{\times}10^9$ Jones (above $1{\times}10^9$) at room temperature, leading to low power consumption

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.660-666
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• 2010

30 nm thick Ni layers were deposited on a glass substrate by e-beam evaporation. Subsequently, 30 nm or 60 nm ${\alpha}-Si:H$ layers were grown at low temperatures ($<220^{\circ}C$) on the 30 nm Ni/Glass substrate by catalytic CVD (chemical vapor deposition). The sheet resistance, phase, microstructure, depth profile and surface roughness of the $\alpha-Si:H$ layers were examined using a four-point probe, HRXRD (high resolution Xray diffraction), Raman Spectroscopy, FE-SEM (field emission-scanning electron microscopy), TEM (transmission electron microscope) and AES depth profiler. The Ni layers reacted with Si to form NiSi layers with a low sheet resistance of $10{\Omega}/{\Box}$. The crystallinty of the $\alpha-Si:H$ layers on NiSi was up to 60% according to Raman spectroscopy. These results show that both nano-scale NiSi layers and crystalline Si layers can be formed simultaneously on a Ni deposited glass substrate using the proposed low temperature catalytic CVD process.

• Korean Journal of Materials Research
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• v.25 no.1
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• pp.1-8
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• 2015

This study suggested comprehensive structural characterization methods for the commercial blue light emitting diodes(LEDs). By using the Z-contrast intensity profile of Cs-corrected high-angle annular dark field scanning transmission electron microscope(HAADF-STEM) images from a commercial lateral GaN-based blue light emitting diode, we obtained important structural information on the epilayer structure of the LED, which would have been difficult to obtain by conventional analysis. This method was simple but very powerful to obtain structural and chemical information on epi-structures in a nanometer-scale resolution. One of the examples was that we could determine whether the barrier in the multi-quantum well(MQW) was GaN or InGaN. Plan-view TEM observations were performed from the commercial blue LED to characterize the threading dislocations(TDs) and the related V-pit defects. Each TD observed in the region with the total LED epilayer structure including the MQW showed V-pit defects for almost of TDs independent of the TD types: edge-, screw-, mixed TDs. The total TD density from the region with the total LED epilayer structure including the MQW was about $3.6{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion as 80%: 7%: 13%. However, in the mesa-etched region without the MQW total TD density was about $2.5{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion of 86%: 5%: 9 %. The higher TD density in the total LED epilayer structure implied new generation of TDs mostly from the MQW region.

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.362-366
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• 2008

The precipitation behavior in Mg-6 wt%Zn-1 wt%Y alloy annealed at different temperatures of $200^{\circ}C$ and $400^{\circ}C$ has been characterized by high resolution transmission electron microscope. When the alloy is annealed at $200^{\circ}C$ for 6 hr, the plate- and the rod-shaped ${\beta}_2'$ phases are precipitated in the matrix. The orientation relationship of plate-shaped precipitates with the matrix exhibits a [$11{\bar{2}}0]{\beta}_2$ || [$10{\bar{1}}0$]Mg, $(0001){\beta}_2'$ || (0001)Mg. While the rod-shaped precipitates have two kinds of the orientation relationships with the matrix, i.e. $[11{\bar{2}}0]{\beta}_2'$||[0001] Mg, $(0001){\beta}_2'||(11{\bar{2}}0)$ Mg and $[11{\bar{2}}0]{\beta}_2'$||[0001] Mg, $({\bar{1}}106){\beta}_2'||(10{\bar{1}}0)$ Mg. With increasing annealing time at $200^{\circ}C$ the ${\beta}_1'$ phases are also precipitated in the matrix and the orientation relationship exhibits a $[010]{\beta}_1'$ || [0001]Mg, $(603){\beta}_1'$ || ($01{\bar{1}}0$)Mg between the ${\beta}_1'$ precipitate and the matrix. The icosahedral phases are precipitated in the alloy annealed at $400^{\circ}C$ and exhibit a $[I2]_I$ || [0001]Mg relationship with the matrix.

• Journal of the Korean Society of Visualization
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• v.2 no.1
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• pp.12-17
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• 2004

The physical characteristics of soot near the soot inception point were investigated with various measurements. In-situ measurements of particle size and volume fraction were introduced based on time resolved laser-induced incandescence (TIRE-LII) and laser-induced ion mobility (LIIM). The one has more convenience and accuracy than conventional LII technique and the other works best for particle sizes of a few nanometers at high concentrations in a uniform concentration field. A complementary ex-situ measurement of particle size is nano differential mobility analyzer (Nano-DMA), which recently developed for measuring particle sizes between 2nm and 100nm and provides high-resolution size information for early soot. Particles will be also collected on transmission electron microscope (TEM) grids using rapid thermophoretic sampling and analyzed for morphology. These measurements will allow fresh and original insight into the characterizing soot inception process. The measured physical properties of incipient soot will clarify the controlling growth mechanism combined with chemical ones, and the dominant mechanism for soot modeling can be deduced from the information.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.79-83
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• 2003

The microstructure of bulk electrolytic MnO₂ (EMD) was studied using x-ray diffraction and transmission electron microscopy (TEM). The bulk sample showed a typical powder x-ray diffraction pattern of EMD materials. TEM study showed that the structure of EMD is present at two length scales;grains, ∼0.2 ㎛ in diameter, and ∼10 nm crystallites within the grain. The electron beam microdiffraction study revealed that each grain is an assemblage of multiphase with a common crystallographic orientation, and_that ∼50% of the crystallites are Ramsdellite, ∼30% are ε-MnO₂, and ∼15% are Pyrolusite. The ｛1120｝peak located at about 67° in powder XRD pattern as well as a high-resolution electron microscope (HREM) image of (0001) plane support the existence of ε-MnO₂ phase.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.51-57
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• 2008

we have demonstrated structural evolution and optical properties of Si-nanowires (NWs) synthesized on Si (111) substrates with nanoscale Au-Si islands by rapid thermal chemical vapor deposition (RTCVD). The Au-Si nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. The Si-NWs were grown by a mixture gas of SiH4 and H2 at a pressure of 1.0 Torr and temperatures of $500{\sim}600^{\circ}C$. Scanning electron microscopy measurements showed that the Si-NWs are uniformly sized and vertically well-aligned along <111> direction on Si (111) surfaces. The resulting NWs are ${\sim}60nm$ in average diameter and ${\sim}5um$ in average length. High resolution transmission microscopy measurements indicated that the NWs are single crystals covered with amorphous SiOx layers of ${\sim}3nm$ thickness. In addition, the optical properties of the NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si main optical phonon peak were observed in Raman spectra of Si-NWs, which indicates a minute stress effects on Raman spectra due to a slight lattice distortion led by lattice expansion of Si-NW structures.

• Particle and aerosol research
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• v.9 no.4
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• pp.209-219
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• 2013

We have used the modified diffusion flame burner to synthesize silica coated iron oxide nanoparticles having enhanced superparamagnetic property. Silica-encapsulated iron oxide particles were directly observed using a high resolution transmission electron microscope. From the energy dispersive X-ray spectroscopy (EDS) and zeta potential measurements, the iron oxide particles were found to be completely covered by a silica coating layer. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements revealed that the iron oxide core consists of ${\gamma}-Fe_2O_3$ rather than ${\alpha}-Fe_2O_3$. Our magnetization measurements support this conclusion. Biocompatibility test of the silica-coated iron oxide nanoparticles is also conducted using the protein adsorption onto the coated particle.