• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1365-1368
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• 2004

A scheme to control the laser power and the exposure time was studied to fabricate precise microstructures using the nanostereolithography (nSL) process. Some recent works have shown that a three-dimensional (3D) microstructure can be fabricated by the photopolymerizing process which is induced by two-photon absorption (TPA) with a femtosecond pulse laser. TPA provides the ability to confine photochemical and physical reactions within the order of laser wavelength, so neardiffraction limit features can be produced. In the nSL process, voxels are continuously generated to form a layer and then another layer is stacked in the normal direction of a plane to construct a 3D structure. Thus, fabrication of a voxel with low aspect ratio and small diameter is one of the most important parameters for fabricating precise 3D microstructures. In this work, the mechanism of a voxel formation is studied and a scheme on the control of laser power and exposure for minimizing aspect ratio of a voxel is proposed.

• Journal of Sensor Science and Technology
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• v.24 no.1
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• pp.41-46
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• 2015

In this work, pure hierarchical ZnO structure was prepared using a simple hydrothermal method, and Ag nanoparticles doped hierarchical ZnO structure was synthesized uniformly through photochemical route. The reduced graphene oxide (rGO) has been synthesized by typical Hummer's method and reduced by hydrazine. Prepared Ag/ZnO nanostructures are uniformly dispersed on the surface of rGO sheets using ultrasonication process. The synthesized samples were characterized by SEM, TEM, EDS, XRD and PL spectra. The average size of prepared ZnO microspheres was around $2{\sim}3{\mu}m$ and showed highly uniform. The average size of doped-Ag nanoparticles was 50 nm and decorated into ZnO/rGO network. The $C_2H_2$ gas sensing properties of as-prepared products were investigated using resistivity-type gas sensor. Ag/ZnO-rGO based sensors exhibited good performances for $C_2H_2$ gas in comparison with the Ag/ZnO. The $C_2H_2$ sensor based on Ag/ZnO-rGO had linear response property from 3~1000 ppm of $C_2H_2$ concentration at working temperature of $200^{\circ}C$. The response values with 100 ppm $C_2H_2$ at $200^{\circ}C$ were 22% and 78% for Ag/ZnO and Ag/ZnO-rGO, respectively. In additions, the sensor still shows high sensitivity and quick response/recovery to $C_2H_2$ under high relative humidity conditions. Moreover, the device shows excellent selectivity towards to $C_2H_2$ gas at optimal working temperature of $200^{\circ}C$.

• Korean Chemical Engineering Research
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• v.55 no.6
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• pp.731-744
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• 2017

Triplet-triplet annihilation upconversion (TTA-UC) is a special photochemical process that converts low energy photons to higher energy photon via combination of organic chemicals which fulfill specific energetic criteria. TTA-UC has been known as attractive technology that is able to enhance energy conversion efficiency of the photonic devices based on sunlight, which is achieved by conversion of wasted low energy photons in solar spectrum into higher energy photon. In the present paper, we introduced the photochemical mechanism and characteristics of TTA-UC phenomenon, which is yet unfamiliar to the domestic academia, and investigated recent research status, application, and future research directions of TTA-UC technology.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.513-517
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• 2010

There have been many efforts to modify and improve the properties of functional thin films by hybridization with nano-sized materials. For the fabrication of electronic circuits, micro-patterning is a commonly used process. For photochemical metal-organic deposition, photoresist and dry etching are not necessary for microscale patterning. We obtained direct-patternable $SnO_2$ thin films using a photosensitive solution containing Ag nanoparticles and/or multi-wall carbon nanotubes (MWNTs). The optical transmittance of direct-patternable $SnO_2$ thin films decreased with introduction of nanomaterials due to optical absorption and optical scattering by Ag nanoparticles and MWNTs, respectively. The crystallinity of the $SnO_2$ thin films was not much affected by an incorporation of Ag nanoparticles and MWNTs. In the case of mixed incorporation with Ag nanoparticles and MWNTs, the sheet resistance of $SnO_2$ thin films decreased relative to incorporation of either single component. Valence band spectral analyses of the nano-hybridized $SnO_2$ thin films showed a relation between band structural change and electrical resistance. Direct-patterning of $SnO_2$ hybrid films with a line-width of 30 ${\mu}m$ was successfully performed without photoresist or dry etching. These results suggest that a micro-patterned system can be simply fabricated, and the electrical properties of $SnO_2$ films can be improved by incorporating Ag nanoparticles and MWNTs.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.179-183
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• 2011

In this study, photochemical effects (OH radical formation) in the photoreactor was investigated to analyze UV-C intensity distribution. In addition, The influence radius of the UV-C lamp was measured at various dose of $TiO_2$ (Degussa P-25). The photoreactor used in this study was bath type reactor which is made by acrylic and the UV-C lamp (SANKYO DENKI, wavelength : 254 nm, Diameter : 2.2 cm, Length : 18.5 cm) was used as photo source. The maximum electric power consumption of the UV lamp was 10.5 W. The OH radical formation by UV-C was measured by KI dosimetry methods. From the results, the effective OH radical formation was occurred under the following condition. The reasonable distance of UV-C lamp is within 13 cm and the intensity of UV-C lamp should be more than 0.367 mW/$cm^2$. Moreover, the concentration of catalyst affects on the influence radius of the UV lamp.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.369-369
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• 2007

ZnO film has been investigated during several decades because it has excellent optical property like a transmittance among the range of visible light for using transparent conducting oxide (TCO) films. But ZnO film has not enough conductivity for applying to TCO devices. Therefore we synthesized platinum nanoparticles and they incorporated into ZnO due to improve the electrical property of ZnO film by sol-gel synthesis method. Also, we fabricated photosensitive ZnO thin film containing Pt nanoparticles by sol-gel process and spin-coating for using photochemical solution deposition. Photosensitive ZnO film could carry out the direct-pattern which allow the etching process to be convenient. The optical and electrical properties of ZnO film with or without various atomic percent of Pt nanoparticles annealed at various temperatures were investigated by using UV-Vis spectroscopy and 4-point probe method, respectively. We characterized the ZnO thin film containing Pt nanoparticles using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy.

• Journal of Korean Society on Water Environment
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• v.21 no.3
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• pp.284-288
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• 2005

In this study, photochemical advanced oxidation processes (AOPs) utilizing the Photo Fenton reaction ($Fe^{2+}+H_2O_2+UV$) were investigated in lab-scale experiments for the treatment of livestock wastewater. For the experimets, the livestock wastewater was pretreated by coagulation with $3,000mg/L\;FeCl_3$. The optimal conditions for Photo-Fenton processes were determined: pH was 5, the concentration of ferrous ion (Fe II) was 0.01 M. The concentration of hydrogen peroxide was 0.1 M, and molar ratio ($Fe^{2+}/H_2O_2$) was 0.1. The optimal reaction time was 80 min. Under the optimal condition of Photo-Fenton process, chemical oxygen demand (COD), color and fecal coliform removal efficiencies were about 79, 70, and 99.4%, respectively and sludge production was 7.5 mL from 100 mL of solution.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.312-320
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• 2003

The basic mechanistic aspects of the interaction and practical considerations related to polymer ablation were briefly reviewed. Photochemical and photothermal effects, which highly depend on laser wavelength have close correlation with each other. In this study, multi-scanning laser ablation processing of polymer with a DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO$_4$ laser (355 nm) was developed to fabricate a three-dimensional micro shape. Polymer fabrication using DPSSL has some advantages compared with the conventional polymer ablation process using KrF and ArF laser with 248 nm and 193 nm wavelength. These advantages include pumping efficiency and low maintenance cost. And this method also makes it possible to fabricate 2D patterns or 3D shapes rapidly and cheaply because CAD/CAM software and precision stages are used without complex projection mask techniques. Photomachinability of polymer is highly influenced by laser wavelength and by the polymer's own chemical structure. So the optical characteristics of polymers for a 355 nm laser source is investigated experimentally and theoretically. The photophysical and photochemical parameters such as laser fluence, focusing position, and ambient gas were considered to reduce the plume effect which re-deposits debris on the surface of substrate. These phenomena affect the surface roughness and even induce delamination around the ablation site. Thus, the process parameters were tuned to optimize for gaining precision surface shape and quality. This maskless direct photomachining technology using DPSSL could be expected to manufacture tile prototype of micro devices and molds for the laser-LIGA process.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.05b
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• pp.345-346
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• 2003

도시의 대기오염 문제는 다양한 배출원으로부터 다량 및 다종의 오염물질 배출과 그 지역의 도시화에 따른 기후특성과 관련된다. 대기오염물질의 분포 양상은 대기오염물질의 배출량과 난류 확산 및 수송, 화학 반응, 침적 현상 등에 의해 결정되므로 이들을 지배하는 기상인자들에 대한 이해는 대기오염현상을 파악하는 필수 요소라고 할 수 있다(Lalas et al., 1982 ; Liu et al., 1994). 도시규모의 기후 특징은 도시내에 형성된 고유의 기상장이 대기오염물질을 정체시킨다는 것이다(Noto, 1996). (중략)

• Journal of Environmental Science International
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• v.12 no.7
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• pp.825-833
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• 2003

The emission of volatile organic compounds (VOCs) generated from painting and coating processes is a worldwide problem as contributing factors to the development of photochemical smog and other environmental problems. Common methods of reducing VOC emissions are adsorption on activated carbon, membrane separation, absorption, incineration, or catalytic oxidation. In this article, the environmental issues caused by VOC emissions and the trend of legislation against such emissions will be surveyed first. Several conventional control technologies will then be summarized and the characteristics of each process will be introduced. Lastly, some examples will be described to show the hybrid processes which have been industrially applied for the recovery of VOC.