• Korean Journal of Materials Research
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• v.9 no.9
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• pp.861-864
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• 1999

A new plasma source using the multi-cathode electron beam has been designed and manufactured. A multi-cathode was adopted to produce bulk plasmas in a large volume. Multi-cathode electron beam plasma source(MCEBPS) was found to generate stable plasmas over the wafer diameter of 300 mm or above. W(tungsten) filament was used as a cathode. Over a 320 mm diameter, both the plasma potential $V_p$ and floating potential $V_f$ were uniformly maintained and the difference between $V_p and V_f$ was measured to be small. The plasma density was around $10^{10} cm^{-3}$ and its variation along the radial distance was small.

• Vacuum Magazine
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• v.2 no.2
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• pp.24-28
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• 2015

The brightness of an electron source, along with the aberrations of an objective lens, determines the image resolution and beam current on samples, which are two important parameters for evaluating the performance of an electron microscope. Here we introduce thermal electron source, Schottky emitter and cold field electron emitter. Thermal electron source is the cheapest and stable electron source but it has the lowest brightness. Schottky emitter is 10000 times brighter than tungsten thermal electron source, but requires ultrahigh vacuum operating condition. Cold field electron emitter is 10 times brighter than Schottky emitters, but it is rather unstable and its operation requires most stringent vacuum condition, hindering its widespread use.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.403-408
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• 2011

To develop the MFX (Micro-Focus X-ray) tube, the trajectories of electrons emitted from the field emission cathode was simulated using SIMION program. Regardless of starting position of the electron in emitter, we found out the fact that there is the optimum extractor voltage Ve, which can focus the electron beam on one place. Extractor voltage Ve varies depending on the source voltage Vs, but the ratio of two voltages (Ve/Vs) is always constant, its value was 99.4%. When the ratio of two voltages (Ve/Vs) was 99.4%, the beam diameter in the cross-over point was $1.2{\mu}m$. Because the focal spot size in MFXG (Micro-Focus X-ray Generator) can not be less than the cross-over diameter within MFX tube, it is important to find out the conditions that can make a smaller beam diameter. Therefore, the above results is considered to be a very important ones in the development of the MFXG.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.171.1-171.1
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• 2015

Carbon nanotube emitters is very promising electron emitter for electron beam applications. We introduced the carbon nanotube electron beam (C-beam) exposure technic using triode structure. As a source, the electron beam emit from CNT emitters placed at the cathode by high electric field. Through the gate mesh, with high accelerating energy, the electron can be extracted easily and impact at the anode plate. For thin film modification, after the C-beam exposure on the amorphous silicon thin film, we found phase changes and it showed a high crystallinity from the Raman measurement. We expect that this crystallized film will be a good candidate as a new active layer of TFT.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.49-54
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• 2017

In this study, the volumetric heat source in electron beam welding (EBW) is modeled through finite element method taking advantage of ABAQUS software package. Since this welding method is being applied in plates with different thicknesses and also considering that residual stresses reduce the strength of these weldments, the effect of thickness in the distribution and magnitude of residual stresses after welding is studied. Regarding the vast application of Inconel 706 super-alloy in aerospace industries, this material was selected in the current research. In order to validate the finite element model, the obtained results were compared to those of other researchers in this area, and good agreement was observed. The simulation results revealed that increase in the plate thickness leads to increase in the residual stresses. In addition heat treatment in the base metal (before welding) increases the residual stresses significantly.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.9
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• pp.1281-1285
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• 2014

Recently, as the wide spread of smart phone, pico projector which is used at the smart phone is appeared as a portable display device. In this paper, among several pico projectors, laser beam scanner module is dealt with in which laser is used as light source, and mems-mirror is used as optical panel. In this device, screen image quality is a special issue, and blur effect is a typical adverse effect to the quality of this device. So the enhancement of this blur effect has an important factor of the quality of the device. The definition of the blur and the main source of the blur are studied and the simulation results and way of improvement are also suggested.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.190-193
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• 2003

The DOA(Direction Of Arrival) estimation to select a best beam for receiving a particular signal in switched beam antenna systems, and to shape the optimal beam in adaptive array antenna systems, is typically performed under the assumption that the target user motion is almost negligible. In this paper, we model the user as the time-varying source and adopt the LPA(Local Polynomial Approximation) tracking algorithm, proposed by Katkovnik, to solve the time-varying DOA estimation problem. Then, we compare the power spectrum functions between the LPA beamformer and the conventional beamformer, also, the normalized SNRs of each beamformer. The results show that the LPA beamformer is robuster than the conventional beamformer in tine-varying environments. In addition, in case of the conventional beamformer, more array elements give rise to more degradation in the aspect of SNR.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.515-518
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• 1994

Holographic interferometry is a useful whole-field nondestructive testing for measuring deformations and vibrations of engineering structure. A diverging beam is used as a light source int the most of holographic interferometer practically. For a relatively small object the optical arrangement using a collimated light source has no difficulty in use technically, but for a large object it is difficult to use a collimated beam. In this study we calculate the error of measured displacement from the sensitivity vector dominated by the geometry of optical arrangement for holographic interferometer and show the result obtained with 2-D plots. A Plane surface and a cylindrical surface were chosen as objects to be calculated and computer analysis was carried out for the cases of a diverging beam and a collimated one.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.242-247
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• 2009

The ability of time reversal techniques to focus ultrasonic beams on the source location is important in many aspects of ultrasonic nondestructive evaluation. In this paper, we investigate the time reversal beam focusing of ultrasonic array sensors on a defect in layered media. Numerical modeling is performed using the commercially available software which employs a time domain finite difference method. Two different time reversal approaches are considered - the through transmission and the pulse-echo. Linear array sensors composed of N elements of line sources are used for signal reception/excitation, time reversal, and reemission in time reversal processes associated with the scattering source of a side-drilled hole located in the second layer of two layer structure. The simulation results demonstrate the time reversal focusing even with multiple reflections from the interface of layered structure. We examine the focusing resolution that is related to the propagation distance, the size of array sensor and the wavelength.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.497-497
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• 2012

산업의 발전함에 따라 고기능성 박막의 수요가 증가하고 있으며, magnetron sputtering, e-beam evaporation, ion beam 등을 이용한 박막 증착에 대한 연구가 많이 진행되고 있다. 그러나 기존 방법만으로는 박막 접착계면의 불균일로 인해 고기능성 박막 성장이 어렵다는 단점을 가지고 있다. 이러한 문제를 해결하기 위하여 박막 공정 중 고밀도 플라즈마 소스(high density plasma source)를 통해 추가적인 에너지를 인가하여 박막의 밀도를 bulk 수준으로 증가시키고 내부 응력을 조절하는 연구에 대한 관심이 커지고 있다. 특히 grid를 이용하여 플라즈마 내 이온의 입사에너지를 증가시킴으로써, 기존 공정보다 고기능성 박막을 구현할 수 있다. 본 연구에서는 RF power를 이용한 inductively coupled plasma를 통해 플라즈마를 생성시킨 후 grid에 DC power를 인가하는 플라즈마 소스를 개발하였으며, 시뮬레이션을 통해 plasma density와 ion current density, ion energy 분석 및 grid 디자인을 하였다. 개발된 플라즈마 소스는 ion energy analyzer를 통해 RF power 및 grid에 인가하는 power의 세기에 따라 이온화 정도 및 이온의 입사에너지를 측정하였다.