• 한국레이저가공학회지
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• 제5권2호
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• pp.31-38
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• 2002

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 ㎱, fluence 0.8∼2.0 J/㎠). Microparticles of mean diameter 18∼80 ㎛ 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.

• 한국레이저가공학회지
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• 제18권4호
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• pp.17-22
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• 2015

In this paper, ablation rate of $Al_2O_3$ ceramics by femtosecond laser fluence is derived with experimental method. The automatic three axis linear stage makes laser optics to move with high spatial resolution. With 10 times objective lens, minimal pattern width of $Al_2O_3$ is measured in the focal plane. Ablated surface area is shown as linear tendency increasing number of machining times with various laser power conditions. Machining times is most sensitive condition to control $Al_2O_3$ pattern width. Also, the linear increment of pattern width with laser power change is investigated. In high machining speed, the ablation volume rate is more linear with fluence because pulse overlap is minimized in this condition. Thermal effect to surrounding medium can be minimized and clean laser process without melting zone is possible in high machining speed. Ablation volume rate decelerates as increasing machining times and multiple machining times should be considered to achieve proper ablation width and depth.

• Advances in nano research
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• 제1권4호
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• pp.219-228
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• 2013

We report on the preparation of iron pyrite ($FeS_2$) using pulsed electron ablation of two targets, namely, a mixture of sulfur and iron compound target, and a natural iron pyrite target. Thin films of around 50 nm in thickness have been deposited on glass substrates under Argon background gas at 3 mTorr, and at a substrate temperature of up to $450^{\circ}C$. The thin films have been analyzed chemically and examined structurally using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and visible Raman spectroscopy. The morphology and thickness of the films have been assessed using scanning electron microscopy (SEM) and visible spectroscopic reflectance. The preliminary findings, using a synthetic target, show the presence of iron pyrite with increasing proportion as substrate temperature is increased from $150^{\circ}C$ to $250^{\circ}C$. The data have not shown any evidence of pyrite in the deposited films from a natural target.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.103-103
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• 2003

ZnO$_{1-x}$(또는 Zn$_{1+x}$O) 산화아연은 과잉의 아연(또는 oxygen vacancy)이 도우너(donor) 역할을 하는 비화학양론적 n형 산화물 반도체이다. ZnO는 높은 투과율을 가지고 온도나 주변환경에 대해 매우 안정하며, 또한 이미 상용화된 ITO (Indium tin oxide)에 비해 식각 특성이 우수하고, 수소 플라즈마에 대한 저항성이 크다는 장점 때문에 가스센서와 디스플레이용 소자 등 다양한 분야에 응용이 가능하다. ZnO 박막은 CVD, Reactive Magnetron Sputtering, Electron-beam Evaporation 등 여러 가지방법으로 제작할 수 있다. 본 연구에서는 형성된 박막의 구성성분이 타겟의 성분과 유사하고 낯은 기판온도에서도 박막이 형성되어지는 장점을 가지는 Pulsed Laser Deposition 방법을 사용하여 유리 기판위에 ZnO 박막을 형성하였다.다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 춘계학술대회 논문집
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• pp.111-112
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• 2009

Diamond-like carbon (DLC) is a convenient term to indicate the compositions of the various forms of amorphous carbon (a-C), tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon and tetrahedral amorphous carbon (a-C:H and ta-C:H). The a-C film with disordered graphitic ordering, such as soot, chars, glassy carbon, and evaporated a-C, is shown in the lower left hand corner. If the fraction of sp3 bonding reaches a high degree, such an a-C is denoted as tetrahedral amorphous carbon (ta-C), in order to distinguish it from sp2 a-C [2]. Two hydrocarbon polymers, that is, polyethylene (CH2)n and polyacetylene (CH)n, define the limits of the triangle in the right hand corner beyond which interconnecting C-C networks do not form, and only strait-chain molecules are formed. The DLC films, i.e. a-C, ta-C, a-C:H and ta-C:H, have some extreme properties similar to diamond, such as hardness, elastic modulus and chemical inertness. These films are great advantages for many applications. One of the most important applications of the carbon-based films is the coating for magnetic hard disk recording. The second successful application is wear protective and antireflective films for IR windows. The third application is wear protection of bearings and sliding friction parts. The fourth is precision gages for the automotive industry. Recently, exciting ongoing study [1] tries to deposit a carbon-based protective film on engine parts (e.g. engine cylinders and pistons) taking into account not only low friction and wear, but also self lubricating properties. Reduction of the oil consumption is expected. Currently, for an additional application field, the carbon-based films are extensively studied as excellent candidates for biocompatible films on biomedical implants. The carbon-based films consist of carbon, hydrogen and nitrogen, which are biologically harmless as well as the main elements of human body. Some in vitro and limited in vivo studies on the biological effects of carbon-based films have been studied [$2{\sim}5$].The carbon-based films have great potentials in many fields. However, a few technological issues for carbon-based film are still needed to be studied to improve the applicability. Aisenberg and Chabot [3] firstly prepared an amorphous carbon film on substrates remained at room temperature using a beam of carbon ions produced using argon plasma. Spencer et al. [4] had subsequently developed this field. Many deposition techniques for DLC films have been developed to increase the fraction of sp3 bonding in the films. The a-C films have been prepared by a variety of deposition methods such as ion plating, DC or RF sputtering, RF or DC plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance chemical vapor deposition (ECR-CVD), ion implantation, ablation, pulsed laser deposition and cathodic arc deposition, from a variety of carbon target or gaseous sources materials [5]. Sputtering is the most common deposition method for a-C film. Deposited films by these plasma methods, such as plasma enhanced chemical vapor deposition (PECVD) [6], are ranged into the interior of the triangle. Application fields of DLC films investigated from papers. Many papers purposed to apply for tribology due to the carbon-based films of low friction and wear resistance. Figure 1 shows the percentage of DLC research interest for application field. The biggest portion is tribology field. It is occupied 57%. Second, biomedical field hold 14%. Nowadays, biomedical field is took notice in many countries and significantly increased the research papers. DLC films actually applied to many industries in 2005 as shown figure 2. The most applied fields are mold and machinery industries. It took over 50%. The automobile industry is more and more increase application parts. In the near future, automobile industry is expected a big market for DLC coating. Figure 1 Research interests of carbon-based filmsFigure 2 Demand ratio of DLC coating for industry in 2005. In this presentation, I will introduce a trend of carbon-based coating research and applications.