• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.267.2-267.2
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• 2016

Semiconductor photo-catalysis offers the potential for complete removal of toxic chemicals through its effective and broad potential applications. Various new compounds and materials for chemical catalysts were synthesized in the past few decades. As one of the most important II-VI group semiconductors, zinc sulfide (ZnS) with a wide direct band gap of 3.8 eV has been extensively investigated and used as a catalyst in photochemistry, environmental protection and in optoelectronic devices. In this work, the ZnS films and nanostructures have been successfully prepared by wet chemical method. We show that the agglomerates with four successive scales are always observed in the case of the homogeneous precipitation of zinc sulfide. Hydrodynamics plays a crucial role to determine the size of the largest agglomerates; however, other factors should be invoked to interpret the complete structure. In addition, studies of the photocatalytic properties by exposure to UV light irradiation demonstrated that ZnS nanocrystals (NCs) are good photo-catalysts as a result of the rapid generation of electron-hole pairs by photo-excitation and the highly negative reduction potentials of excited electrons. A combination of their unique features of high surface-to volume ratios, carrier dynamics and rich photo-catalytic suggests that these ZnS NCs will find many interesting applications in semiconductor photo-catalysis, solar cells, environmental remediation, and nano-devices.

• Advances in nano research
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• v.8 no.3
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• pp.191-202
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• 2020

The article brings the study of nonlocal, surface and the couple stress together to apparent the frequency retaliation of FG nanobeams (Functionally graded). For the examination of frequency retaliation, the article considers the accurate spot of neutral axis. This article aims to enhance the coherence of proposed model to accurately encapsulate the significant effects of the nonlocal stress field, size effects together with material length scale parameters. These considered parameters are assimilated through what are referred to as modified couple stress as well as nonlocal elasticity theories, which encompasses the stiffness-hardening and softening influence on the nanobeams frequency characteristics. Power-law distribution is followed by the functional gradation of the material across the beam width in the considered structure of the article. Following the well-known Hamilton's principle, fundamental basic equations alongside their correlated boundary conditions are solved analytically. Validation of the study is also done with published result. Distinct parameters (such as surface energy, slenderness ratio, as nonlocal material length scale and power-law exponent) influence is depicted graphically following the boundary conditions on non-dimensional FG nanobeams frequency.

• Journal of information and communication convergence engineering
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• v.14 no.1
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• pp.35-39
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• 2016

In this paper, we develop a 94-GHz single balanced mixer with low conversion loss using planar Schottky diodes on a GaAs substrate. The GaAs Schottky diode has a nanoscale anode with a T-shaped disk that can yield high cutoff frequency characteristics. The fabricated Schottky diode with an anode diameter of 500 nm has a series resistance of 21 Ω, an ideality factor of 1.32, a junction capacitance of 8.03 fF, and a cutoff frequency of 944 GHz. Based on this technology, a 94-GHz single balanced mixer was constructed. The fabricated mixer shows an average conversion loss of -7.58 dB at an RF frequency of 92.5 GHz to 95 GHz and an IF frequency of 500 MHz with an LO power of 7 dBm. The RF-to-LO isolation characteristics were greater than -32 dB. These values are considered to be attributed to superior Schottky diode characteristics.

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.85-89
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• 2009

Nano-crystalline hydroxyapatite (HAp) films were formed at the Ti surface by a single-step microarc oxidation (MAO), and HAp-zirconia composite (HZC) films were obtained by subsequent chemical vapor deposition (CVD) of zirconia onto the HAp. Through the CVD process, zero- and one-dimensional zirconia nanostructures having tetragonal crystallinity (t-ZrO2) were uniformly distributed and well incorporated into the HAp crystal matrix to form nanoscale composites. In particular, (t-$ZrO_2$) was synthesized at a very low temperature. The HZC films did not show secondary phases such as tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP) at relatively high temperatures. The most likely mechanism for the formation of the t-$ZrO_2$ and the pure HAp at the low processing temperature was proposed to be the diffusion of $Ca^{2+}$ ions. The HZC films showed increasing micro-Vickers hardness values with increases in the t-$ZrO_2$ content. The morphological features and phase compositions of the HZC films showed strong dependence on the time and temperature of the CVD process. Furthermore, they showed enhanced cell proliferation compared to the $TiO_2$ and HAp films most likely due to the surface structure change.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.185-185
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• 2009

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. Using the flexural vibration mode of PZT bar, a piezopump is successfully made. The PZT bar is polarized with thickness direction. The proposed structure for the piezo-pump consists of an input and an output port, piezoelectric ceramic actuator, actuator support, diaphragm. The traveling flexural wave along the bar is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. Fluid is drawn into a forming chamber, eventually the forming chamber closes trapping the fluid therein. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump the highest pressure level of 83.4kHz.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.3
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• pp.125-129
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• 2009

The preparation and characterization of niobium carbide crystallites were investigated in this study, and in particular, the effect of preparation conditions were studied on the synthesis of niobium carbides crystallites. For this purpose, various characterization techniques including x-ray diffraction, BET surface area, and oxygen uptake measurements were employed to characterize the synthesized niobium carbide crystallites. The niobium carbide crystallites were prepared using niobium oxide and methane gas or methane-hydrogen mixture. Using x-ray diffraction a lattice parameter of $4.45{\AA}$ and a crystallite size ranging from $52{\AA}$ to $580{\AA}$ was found. BET surface areas ranged from $3.2\;m^2/g$ to $16.6\;m^2/g$ and oxygen uptake values varied from $0.5{\mu}mol/g$ to $6.1{\mu}mol/g$. It was observed that niobium carbide crystallites were active for ammonia decomposition reaction. While the BET surface area increased with increasing the oxygen uptake, the conversion of ammonia decomposition reaction decreased. These results indicated that the ammonia decomposition over these materials was considered to be structure-sensitive.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.162-168
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• 2007

Silica wet gels were prepared ken water glass ($29\;wt%\;SiO_{2}$) by using Amberlite as a ion exchange resin. After washing in distilled water, the wet gels were further aged in a solution of TEOS/EtOH to strengthen of 3-dimensional network structure. As increase TEOS content in aging solution, BET surface area and porosity of the ambient dried silica aerogels were significantly decreased, and average pore diameter was also decreased 30 nm to -10 nm. Also, higher density and compressive strength were obtained in case of higher TEOS content. This is due to precipitation of $SiO_{2}$ nano particles by TEOS. Hence, TEOS addition plays an important role of both strengthening and stiffness of silica wet gel network. By adding over 30 vol% TEOS, a crack-free monolithic silica aerogel tiles were obtained and its density, compressive strength, and thermal conductivity were shown $0.232g/cm^{3}$, 7.3 MPa, and 0.029 W/mk, respectivly.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1172-1177
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the change of soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth region). These results provide a clear picture of a transition to mature soot from precursor materials.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3
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• pp.372-379
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• 2013

In this study, we investigated the traits of the clad metals used in hot-rolled clad steel plates. We examined the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516) under the specific circumstances of post heat treatment and whether a weld was multilayered and thick or repeated because of repairs. The test conditions were as follows. The clad steel plates were butt-welded using FCAW/SAW, and the heat treatment was conducted at $625^{\circ}C$, for 80, 160, 320, 640, or 1280 min. The change in the corrosion resistance was evaluated in these specimens. In the case of the carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro- hardness gradually increased and then decreased after 640 min. The elongation and contraction of the area increased gradually. An oxalic acid etch test and EPR test on STS316, a clad metal, showed a STEP structure and no sensitization. From the test results for the multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. In summary, the purpose of this study was to suggest some considerations when developing on-site techniques and evaluate the sensitization of stainless steels.

• Textile Coloration and Finishing
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• v.23 no.3
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• pp.155-162
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• 2011

para-Aramid has limited dyeability because of its highly crystalline structure and compactness. To improve the dyeability of the para-aramid to reactive dyes of bright color in deep shade, the fabrics were photografted under continuous UV irradiation with dimethylaminopropyl methacrylamide and 4-benzoyl benzoic acid as a monomer and a hydrogen -abstractable photoinitiator respectively. A UV energy of 35J/$cm^2$ and a photoinitiator concentration of ten percent or more with respect to the monomer in the formulation was required for optimal photografting. Grafting yield increased with higher monomer application level. Surface analysis indicated significant alterations in the atomic composition of the photografted fabric surface and the fabric surface was covered with the grafted polymers. While the pristine para-aramid fabrics showed no appreciable dyeability to the ${\alpha}$-bromoacrylamide reactive dyes, the grafted para-aramid fabrics enhanced the dyeability to the reactive dyes substantially. In case of C.I. Reactive Blue 50, a K/S value of 8.7 can be obtained with the grafted para-aramid fabrics with a grafting yield of 2.3 %. Also the color fastness properties of the dyed fabrics was excellent in the conditions of washing, rubbing and light irradiation.