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금속 마이크로입자의 레이저 어블레이션(ablation)에 의한 나노입자 합성
장덕석,김동식 한국레이저가공학회 2002 학술발표대회 Vol.2002 No.2
Al, Cu, Ag 마이크로 입자를 자외선 파장의 펄스레이저로 공기 중에서 어블레이션 시켜 20-40 nm 크기의 v-Al_2O_3, CuO, Ag의 나노입자를 제조하였다. 생성된 나노입자의 평균 크기는 레이저 플루언스와 마이크로입자의 압축 시의 압력이 증가함에 따라 커졌고, 부착대 위치와의 관계는 어떤 특정한 지점에서 최소의 크기를 가짐을 알 수 있었다. LAN 기법을 통하여 마이크로입자의 어블레이션 시킬 때 발생하는 충격파는 벌크시편 및 압밀 시편을 이용하였을 때와 비교하여 매우 약하였고, 이는 레이저 에너지의 효율이 매우 낮음을 보여주는 증거이다. 광굴절법과 레이저 섬광사진법을 통해 펄스레이저에 의해 발생한 충격파는 약 800-2000 m/s의 값을 가지고 전파되며, 시편 근처에서 형성된 어블레이션 플룸은 약 40m/s의 매우 작은 속도로 충격파의 뒤를 따라 전파됨을 알 수 있었다.
장덕석,김동식 한국레이저가공학회 2008 한국레이저가공학회지 Vol.11 No.1
Laser micromachining is a promising technique to fabricate the micro-scale devices. However, there remains important challenges to reducethe redeposition of ablated materials around the laser irradiated zone and to get a smooth surface, especially for metal and semiconductor materials. To achieve the high-quality micromachined devices, various methods have been developed. Liquid-assisted micromachining can be a good solution to overcome the previously mentioned problems. During the laser ablation process, the liquid around the solid sample dramatically changes the ablation characteristics, such as ablation rate, surface profile, formation of debris, and so on. In this investigation, we conducted the laser micromachining of Si in various liquid environmental conditions, such as liquid types, liquid thickness. In addition, using nanoscale time-resolved shadowgraphy technique, we observed the ablation process in liquid environments to understand the mechanism of liquid-assisted laser micromachining.
압밀 금속 마이크로 입자의 펄스 레이저 ABLATION에 의한 나노입자 합성
장덕석,오부국,김동식 한국레이저가공학회 2002 한국레이저가공학회지 Vol.5 No.2
This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ns, fluence 0.8∼2.0 J㎠). Microparticles of mean diameter 18-80 μm are ablated in the ambient air. The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.
장덕석,오준호,이종명,김동식 한국레이저가공학회 2008 한국레이저가공학회 학술대회 논문집 Vol.2008 No.-
It has been shown that the laser shock cleaning (LSC) method is effective to eliminate submicron-scale particulates from solid surfaces. In the LSC process, a high-power laser pulse induces optical breakdown of the ambient gas above the solid surface covered with contaminant particles. The subsuquently created shock wave followed by a high-speed flow stream detaches the particles. In this work, the amplification of shock wave pressure using a Shock wave reflector is introduced and demonstrated, numerically and experimentally. Shock wave reflector increases the shock wave pressure and can remove smaller particle compared with conventional LSC method. According to the numerical calculation, the shock wave pressure is amplified about double times by shock wave reflector. The experimental results conforms that the cleaning force and cleaning efficiency are increased by this method.
액체의 레이저 유기 절연파괴를 이용한 신개념 표면 세정 공정
장덕석(Deoksuk Jang),이종명(Jong-Myoung Lee),김동식(Dongsik Kim) 한국레이저가공학회 2009 한국레이저가공학회지 Vol.12 No.4
The surface cleaning method based on the laser-induced breakdown (LIB) of gas and subsequent plasma and shock wave generation can remove small particles from solid surfaces. In the laser shock cleaning (LSC) process, a high-power laser pulse induces optical breakdown of the ambient gas above the solid surface covered with contaminant particles. The subsequently created shock wave followed by a high-speed flow stream detaches the particles. In this work, a novel surface cleaning process using laser-induced breakdown of liquid is introduced and demonstrated. LIB of a micro liquid jet increases the shock wave intensity and this removes smaller particle than the conventional LSC method. Experiments demonstrate that the cleaning force and cleaning efficiency are also increased significantly by this method.
장덕석(D. Jang),김동식(D. Kim) 한국레이저가공학회 2007 한국레이저가공학회 학술대회 논문집 Vol.2007 No.-
Laser micromachining is promising technique to fabricate the micro-scale device, however, it remains an important challenge that reducing the redeposition of ablated materials around the laser irradiated zone and smoothing the irregular ablated surface, especially in metal and semiconductor processing. To achieve the high-quality micromachined devices, various methods have been developed. Liquid-assisted process can be a good solution to overcome the problems. During the laser ablation process, the liquid around the solid sample dramatically changes the ablation characteristics, such as ablation rate, surface profile, formation of debris, and so on. In this investigation, we conducted the laser micromachining of Si in various liquid environmental conditions, such as liquid types, liquid thickness. In addition, using nanoscale time-resolved shadowgraphy technique, we observed the ablation process in liquid environments to understand the mechanism of liquid-assisted laser processing.
액체 보조 방식의 Excimer 레이저 폴리머 미세가공
장덕석(Deoksuk Jang),김동식(Dongsik Kim) 한국레이저가공학회 2007 한국레이저가공학회지 Vol.10 No.1
Previous studies demonstrated that laser ablation under transparent liquid can result in ablation enhancement and particle removal from the surface. Although the ablation enhancement by liquid is already known for semiconductor and metal, the phenomena of polymer ablation have not been studied. In this work, the liquid-assisted excimer laser ablation process is examined for polymer materials, such as polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) with emphasis on ablation enhancement and surface topography. In the case of PET and PMMA, the effect of liquid is analyzed both for thin water film and bulk water. The results show that application of liquid increases the ablation rate of PMMA while that of PET remains unchanged even in the liquid-assisted process. However, the surface roughness is generally deteriorated in the liquid-assisted process. The surface topography is found to be strongly dependent on the method of liquid application, i.e., thin film or bulk liquid.