• Proceedings of the KSME Conference
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• 2003.04a
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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.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.738-744
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• 2011

The reliability of blade root fixing section is required to endure the centrifugal force and vibration stress for the last stage blade of steam turbine in thermal power plant. Most of the domestic steam turbine last stage blades have finger type roots. The finger type blade is very complex, so the inspection had been performed only on the exposed fixing pin cross-section area due to the difficulty of inspection. But the centrifugal force and vibration stress are also applied at the blade root finger and the crack generates, so the inspection method for finger section is necessary. For the inspection of root finger, inspection points were decided by simulating ultra-sonic path with 3D modeling, curve-shape probe and fixing jig were invented, and the characteristics analysis method of ultrasonic reflection signal and defect signal disposition method were invented. This invented method was actually executed at site and prevented the blade liberation failure by detecting the cracks at the fingers. Also, the same type blades of the other turbines were inspected periodically and the reliability of the turbine increased.

• Journal of the Korean Institute of Telematics and Electronics
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• v.4 no.2
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• pp.3-15
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• 1967

In the design of a portable Gamma-ray transistorized steel pipe thickness gauge, a pulse height discriminator and an anti-coincidence circuit could be eliminated by using a thin, less than 1/2inch, NaI(Tl) scintillation crystal in the detecting probe. This method could provide an economic design and fabrication of a gamma-ray back-scattering gauge allowing allmost the same accuracy and stability compared with the exsisting method. A gauge had been designed and fabricated with the above method and its accuracy was experimentall tested for the 200$^{\circ}C$ high temperature steel pipes. The result showed that the thermal drift was less than y percent which was acceptabel in the practical applications.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.4
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• pp.23-28
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• 2004

In this paper, the properties of Mo as PMOS gate electrodes were studied. The work-function of Mo extracted from C-V characteristic curves was appropriate for PMOS. To identify the electrical and chemical stability of Mo metal gate, the changes of work-function and EOT(Effective Oxide Thickness) values were investigated after 600, 700, 800 and 90$0^{\circ}C$ RTA(Rapid Thermal Annealing). Also it was found that Mo metal gate was stable up to 90$0^{\circ}C$ with underlying SiO$_2$through X-ray diffraction measurement. Sheet resistances of Mo metal gate obtained from 4-point probe were less than 10$\Omega$/$\square$ that was much lower than those of polysilicon.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.234-239
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• 2007

This paper describes the TiW ohmic contact characteristics under the surface treatment of the polycrystalline 3C-SiC thin film grown on $SiO_2/Si(100)$ wafers by APCVD. The poly 3C-SiC surface was polished by using CMP(chemical mechanical polishing) process and then oxidized by wet-oxidation process, and finally removed SiC oxide layers. A TiW thin film as a metalization process was deposited on the surface treated poly 3C-SiC layer and was annealed through a RTA(rapid thermal annealing) process. TiW/poly 3C-SiC was investigated to get mechanical, physical, and electrical characteristics using SEM, XRD, XPS, AFM, optical microscope, I-V characteristic, and four-point probe, respectively. Contact resistivity of the surface treated 3C-SiC was measured as the lowest $1.2{\times}10^{-5}{\Omega}cm^2$ at $900^{\circ}C$ for 45 sec. Therefore, the surface treatments of poly 3C-SiC are necessary to get better contact resistance for extreme environment MEMS applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.401-401
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• 2014

In this study, graphene, the most attractive material today, has been applied to the wavelength-modulated surface plasmon resonance (SPR) sensor. The optical fiber sensor technology is the most fascinating topic because of its several benefits. In addition to this, the SPR phenomenon enables the detection of biomaterials to be label-free, highly sensitive, and accurate. Therefore, the optical fiber SPR sensor has powerful advantages to detect biomaterials. Meanwhile, Graphene shows superior mechanical, electrical, and optical characteristics, so that it has tremendous potential to be applied to any applications. Especially, grapheme has tighter confinement plasmon and relatively long propagation distances, so that it can enhance the light-matter interactions (F. H. L. Koppens, et al., Nano Lett., 2011). Accordingly, we coated graphene on the optical fiber probe which we fabricated to compose the wavelength-modulated SPR sensor (Figure 1.). The graphene film was synthesized via thermal chemical vapor deposition (CVD) process. Synthesized graphene was transferred on the core exposed region of fiber optic by lift-off method. Detected analytes were biotinylated double cross-over DNA structure (DXB) and Streptavidin (SA) as the ligand-receptor binding model. The preliminary results showed the SPR signal shifts for the DXB and SA binding rather than the concentration change.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.206.1-206.1
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• 2014

최근 전자 장비의 금속 전도성 패턴 제작에 있어서 직접적인 프린트가 가능한 프린팅 기술이 기존의 복잡한 photolithography 를 대체할 기술로 주목 받고 있다. 이와 함께 금속 전도성 패턴 제작에 사용되는 고가의 전도성 물질인 Ag ink 및 paste 를 저가의 Cu ink 및 paste 로 대체하기 위한 연구가 진행되고 있다. 하지만 일반적으로 copper 는 대기 중 에서 쉽게 산화되어 높은 저항을 야기시킨다. 따라서 Cu ink 또는 paste 를 제작할 때 copper nanoparticles 을 유기 용매에 분산하여 inert atmosphere에서 합성하거나 [1] copper ink 또는 paste 를 substrate 에 프린트하여 reduction atmosphere 에서 소성시킨다 [2]. 이번 연구에서 Cu paste 를 유리 기판에 screen printing 하여 혼합가스(질소 95%, 수소 5%)와 질소 가스 분위기에서 소성하여 Cu 전극의 소성 거동과 전기적 특성을 분석하였다. 4-point probe를 통해 소성된 Cu 전극의 저항을 측정하여 전도도를 조사하였으며 Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared(FTIR)를 통해 소성된 Cu 전극의 유기물 분해가 전도도에 미치는 영향을 분석하고 Field Emission Scanning Electron Microscopy (FESEM)과 High Resolution Transmission Electron Microscopy (HRTEM)을 통해 Cu nanoparticles 의 grain growth가 전도도에 미치는 영향을 조사하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.55.1-55.1
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• 2010

차세대 디스플레이용 전극 재료는 투명하면서도 낮은 저항값을 가져야 하는 투명 전극 재료로 금속, 금속산화물, 전도성 고분자, 탄소재료 등을 들 수 있다. 금속재료는 전도도는 우수하지만, 낮은 투과도로 투명전극 재료로 적절하지 않고, 대표적인 금속산화물 재료인 indium tin oxide (ITO)의 경우, 우수한 투과성과 낮은 면저항을 기반으로 차세대 디스플레이용 전극으로 현재 사용되고 있다. 하지만 ITO 박막은 휘거나 접을 때 기계적 안정성이 취약한 문제점을 나타내고 있다. 이러한 문제점을 극복하기 위해 전도성과 탄성계수가 높고, 저온에서 대면적 공정이 가능한 CNT을 투명 박막 전극 연구가 활발히 진행되고 있다. 하지만 투명전극 제조시, 탄소 나노튜브 간의 van der waals 인력에 의한 응집 현상으로 인한 분산의 불안정성과 분산제 사용으로 인하여 탄소 나노튜브 박막전극의 전기적, 광학적 특성이 저하를 야기한다. 이에 본 실험에서는 아크 방전 공정으로 합성한 SWCNT 분산액을 사용하여 spray coating 방법으로 glass 위에 박막을 형성하였다. SWCNT 투명 박막 전극 위에 DC sputtering을 이용하여 얇은Ni를 도포한 후, $450{\sim}500^{\circ}C$, ethylene gas 분위기의 thermal CVD방법으로 Carbon NanoFibers (CNFs)를 생성시킴과 동시에 분산제를 burning out하였다. CNF 성장 전후의 투명 박막의 전기적 특성은 four point probe를 이용하여 면저항과 UV-vis 장비를 이용하여 가시광선 영역에서의 광학적 투과도를 측정 비교하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.149-150
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• 2006

We describe a novel method of scanning probe nanofabrication using a AFM(atomic force microscopy) tip with assistance of Femtosecond laser pulses to enhance fabrication capability. Illumination of the AFM tip with ultra-short light pulses induces a strong electric field between the tip and the metal surface, which allows removing metal atoms from the surface by means of field evaporation. Quantum simulation reveals that the field evaporation is triggered even en air when the induced electric field reaches the level of a few volts per angstrom, which is low enough to avoid unwanted thermal damages on most metal surfaces. For experimental validation, a Ti: sapphire Femtosecond pulse laser with 10 fs pulse duration at 800 nm center wavelength was used with a tip coated with gold to fabricate nanostructures on a thin film gold surface. Experimental results demonstrate that fine structures with critical dimensions less than ${\sim}10nm$ can be successfully made with precise control of the repetition rate of Femtosecond laser pulses.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.389-389
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• 2011

Transparent conductive oxide (TCO) 박막은 디스플레이 및 태양전지 등 광범위한 분야에서 적용되고 있으며, 특히 indium tin oxide (ITO)는 낮은 전기적 저항과 우수한 광투과도를 가지고 있어서 이미 많은 분야에 적용되고 있다. 본 연구는 RF와 DC를 혼용한 마그네트론 스퍼터링 공정을 활용하여 ITO 박막 특성 및 이를 활용한 유기태양전지 적용에 관한 것이다. UV-O3 처리된 glass 기판위에 thermal evaporation 방식으로 밀착력을 높이기 위하여 Cr을 5 nm 두께로 증착한 후 Al을 95 nm 증착하였다. 그 위에 스퍼터링 공정으로 ITO 박막을 In2O3:SnO2 target (10wt% SnO2)을 사용하여 1.0 mTorr의 공정압력(Ar:O2=30:1), 50W의 RF power 및 0.11kW의 DC power에서 50~250 nm의 두께로 증착하였다. ITO 박막의 결정구조 및 표면 형상은 x-ray diffraction (XRD) 및 scanning electron microscope (SEM)을 사용하여 분석하였으며, 전기적 특성은 four-point probe법으로 비저항값을 측정하였다. 또한 높은 광변환효율을 가지는 태양전지 제작을 위하여, 다양한 두께의 ITO 박막을 사용하여 ITO/ZnO/P3HT:PCBM/PEDOT/Ag 구조의 유기태양전지를 제작하여 소자 특성을 최적화 하였다.