• 대한전기학회논문지
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• 제44권8호
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• pp.1063-1067
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• 1995

The superconducting properties of YBa$_{2}$Cu$_{3}$$O_{7-x}$(YBaCuO) thin films prepared by laser ablation have been investigated. The x-ray diffraction patterns and surface morphology of the films were substantially different from one another. The compositional ratios of YBaCuO films were controlled by the conditions of the target-substrate distance. The YBaCuO films manufactured on MgO(100) substrate were indicated T$_{c}$(zero)=91.2 K, T$_{c}$(onset)=93 K, and J$_{c}$=3.5*10$^{5}$ A/cm$^{2}$(at 77.3K). The optimum conditions were found to be a substrate temperature of 710 .deg. C, a energy density of 2 J/cm$^{2}$, and a target-substrate distance of 60 mm in an oxygen partial pressure of 200 mTorr.0 mTorr.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.484-487
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• 2001

Amorphous carbon thin films were deposited using laser ablation technique on Si(100) substrates at different temperatures. In this study, effects of the substrate temperature on the properties of amorphous carbon films were systematically investigated. The surface morphologic and structural properties of the films were studied by scanning electron microscopy (SEM) and raman spectroscope, respectively. With increasing of the substrate temperature, the surface morphologies were changed singnificantly. Moreover the intensity ratio of D-band and G-band and the full width at half maximum of these bands were dependent on substrate temperatures.

• 한국결정성장학회지
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• 제24권5호
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• pp.219-223
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• 2014

Pulsed laser ablation in liquid medium was successfully employed to synthesize hydroxyapatite colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the hydroxyapatite nanoparticles were investigated in detail. The obtained hydroxyapatite nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. The laser ablation and the nanoparticle forming process were discussed with explosive ejection mechanism by investigating change of surface morphology on target. The analytical results of XPS, FT-IR and Raman spectroscopy confirms that the stoichiometry and bonding properties of the hydroxyapatite nanoparticles are in good agreement with reported bulk hydroxyapatite materials.

• 동력기계공학회지
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• 제9권4호
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• pp.118-123
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• 2005

We have investigated the fabrication of Si nanoparticles and $C_{60}$ thin films by pulsed laser ablation. By atomic force microscopy(AFM), the laser-deposited $C_{60}$ thin film was verified to have surface far smoother than the surfaces of films produced by the conventional evaporation method. The Si deposited at a He atmosphere of 0.2 Torr was with about $60{\AA}$ height of the Si nanoparticles, suggesting that it was uniformly deposited. We observed visible green emissions spectra in the $Si/C_{60}$ multilayer films after laser annealing. It is considered that this green emissions is occurred from SiC particles, which is produced reaction of Si nanoparticles with $C_{60}$ by laser annealing.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2439-2442
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• 2012

In order to explore the effects of the solvent on the formation rate of polyynes, we investigated the absorption spectra of polyynes obtained by laser ablation of a graphite target in different solvents at 1064 nm. Polyynes so produced were confirmed by the Raman band around $2200cm^{-1}$ which corresponds to the carbon triple bonds. The production of polyynes by laser ablation turned out to be significantly affected by the ratio of the hydrogen and carbon atoms in the solvent molecule. No clear correlations were observed in the formation of polyynes for other properties of the solvent such bond dissociation energy, thermal conductivity, and total mass of hydrogen atoms per volume of solvent.

• 한국레이저가공학회지
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• 제10권2호
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• pp.17-24
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• 2007

We have studied a laser direct writing lithography(LDWL). This is more important to apply to micro patterning using UV laser. We demonstrate the possibility of LDWL and construct the fabrication system. We use Galvano scanner to process quickly micro patterns from computer data. And laser beam is focused with $F-{\theta}$ lens. AZ5214 and SU-8 photoresist are chosen as experimental materials and a kind of well-known positive and negative photoresist respectively. Laser ablation mechanism depends on the optical properties of polymer. In this paper, therefore we investigate the phenomenon of laser ablation according to the laser fluence variation and measure the shape profile of micro patterned holes. From these experimental results, we show that LDWL is very useful to process various micro patterns directly.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1289-1294
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• 2018

The present study aims to investigate experimentally and theoretically thermal ablation in soft tissues by using high intensity focused ultrasound (HIFU) to assess tissue damage during HIFU thermotherapy. The HIFU field was calculated by solving the axisymmetric Khokhlov-Zabolotskaya-Kuznetsov equation from the frequency-domain perspective. The temperature field was calculated by solving Pennes' bioheat transfer equation, and the thermal dose required to create a thermal lesion was calculated by using the thermal dose formula based on the thermal dose of a 240-min exposure at $43^{\circ}C$. In order to validate the simulation results, we performed thermal ablation experiments in a tissue-mimicking phantom and ex-vivo porcine liver for two different HIFU source conditions by using a 1.1-MHz, single-element, spherically focused HIFU transducer. The small difference between the measured and the predicted lesion sizes suggests that the implementation of the numerical model used here should be modified to iteratively allow for temperature-dependent changes in the physical properties of tissues.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1572-1577
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• 2003

High-power pulsed laser ablation under atmospheric pressure is studied utilizing numerical and experimental methods with emphasis on recondensation ratio, and the dynamics of the laser induced vapor flow. In the numerical calculation, the temperature pressure, density and vaporization flux on a solid substrate are first obtained by a heat-transfer computation code based on the enthalpy method, and then the plume dynamics is calculated by using a commercial CFD package. To confirm the computation results, the probe beam deflection technique was utilized for measuring the propagation of a laser induced shock wave. Discontinuities of properties and velocity over the Knudsen layer were investigated. Related with the analysis of the jump condition, the effect of the recondesation ratio on the plume dynamics was examined by comparing the pressure, density, and mass fraction of ablated aluminum vapor. To consider the effect of mass transfer between the ablation plume and air, unlike the most previous investigations, the equation of species conservation is simultaneously solved with the Euler equations. Therefore the numerical model computes not only the propagation of the shock front but also the distribution of the aluminum vapor. To our knowledge, this is the first work that employed a commercial CFD code in the calculation of pulsed ablation phenomena.

• 한국재료학회지
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• 제4권3호
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• pp.339-348
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• 1994

탄소/페놀릭 복합재의 삭마 미세구조와 특성에 대하여 설명하였다. 삭마현상은 추진제와 산화제 사이의 반응에 의한 수증기와 탄산가스의 몰분율에 의해 좌우된다. 그러나, 이 연구논문은 삭마현상이 탄소섬유의 직조형태, 직조밀도, tow크기에 의해서도 변화될 수 있음을 주사전자현미경, 밀도, 열전도도. 삭마표면등을 통해 설명했다. 3가지의 직조형태중, 3K8HS 직조구조가 3K twill구조나 12K8HS구조보다 우수한 내삭마성을 보임을 설명했다.

• 한국정밀공학회지
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• 제22권9호
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• pp.60-68
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• 2005

To investigate the effects of beam focusing in the etching of polymers with short pulse Excimer lasers, a polymer etching model of SSB's is combined with a beam focusing model. Through the numerical simulation, it was found that in the high laser fluence region, SSB model considering both photochemical and thermal contribution is considered to be suitable to predict the etched hole shape than a simple photochemical etching model. The average temperature distribution into the substance obtained by assuming 1-D heat transfer is found to be fairly similar to the fluence distribution on the ablated surface. The experimental etching data fur polymers are used to give material properties for ablation model. The fitted etch depth curve gives a nice agreement with the experimental data.