• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.419-426
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• 2020

Understanding the pore structure including pore shape and connectivity in unconventional reservoirs is essential to increase the recovery rate of unconventional energy resources such as shale gas and oil. In this study, we found analysis condition to probe the nanoscale pore structure in shale reservoirs using Focused Ion Beam (FIB) and Ion Milling System (IMS). A-068 core samples from Liard Basin are used to probe the pore structure in shale reservoirs. The pore structure is analyzed with different pretreatment methods and analysis condition because each sample has different characteristics. The results show that surface milling by FIB is effective to obtain pore images of several micrometers local area while milling a large-area by IMS is efficient to observe various pore structure in a short time. Especially, it was confirmed that the pore structure of rocks with high content of carbonate minerals and high strength can be observed with milling by IMS. In this study, the analysis condition and process for observing the pore structure in the shale reservoirs is established. Further studies are needed to perform for probing the effect of pore size and shape on the enhancement of shale gas recovery.

• Progress in Medical Physics
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• v.27 no.1
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• pp.37-45
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• 2016

In proton therapy, in vivo proton beam range verification is very important to deliver conformal dose to the target volume and minimize unnecessary dose to normal tissue. For this purpose, a multi-slit prompt-gamma camera module made of 24 scintillation detectors and 24-channel signal processing system is under development. In the present study, we have developed and tested a dual-mode signal processing system, which can operate in the energy calibration mode and the fast data acquisition mode, to process the signals from the 24 scintillation detectors. As a result of performance test, using the energy calibration mode, we were able to perform energy calibration for the 24 scintillation detectors at the same time and determine the discrimination levels for the detector channels. Further, using the fast data acquisition mode, we were able to measure a prompt-gamma distribution induced by a 45 MeV proton beam. The measured prompt gamma distribution was found similar to the proton dose distribution at the distal fall-off region, and the estimated beam range was $17.13{\pm}0.76mm$, which is close to the proton beam range of 16.15 mm measured by an EBT film.

• Journal of the Korean Vacuum Society
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• v.12 no.1
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• pp.16-19
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• 2003

Ni thin films on the p-InP (In) substrates were grown at room temperature by using the ion beam-assisted deposition. In order to determine the work function of the Ni thin films, the $\gamma$values were measured as functions of the acceleration voltages by using Ne, Ar, $N_2$. and Xe ion sources. The dependences of the values on various gases and on the acceleration voltages of the focused ion beam were obtained to determine the work function of the Ni thin films. The value of the work function of the Ni thin films grown on the p-InP (100) substrate was 5.8 eV ~ 5.85 eV. These results provide important information on the electronic properties of Ni thin films grown on p-InP (100) substrates at room temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.110-115
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• 2005

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25m plano-convex lens having 2.5mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an optical tweezers type and pure gradient force type. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. Using the optical tweezers type, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about $16\%,\;11.4\%\;and\;9.6\%$ for PSL particle size of $2.5{\mu}m,\;1.0{\mu}m,\;and\;0.5{\mu}m$, respectively. Particle beam width was minimized around the laser power of 0.2W. However, as increasing the laser power higher than 0.4W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. For pure gradient force type, the reduction of the particle beam width was smaller than optical tweezers type but proportional to laser power. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1505-1509
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• 2004

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25 mm plano-convex lens having 2.5 mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an Ar-Ion continuous wave laser and a pulsed Nd-YAG laser. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. For the particle diameter of 0.5 ${\mu}m$, the particle beam was broken due to the secondary flow at Reynolds number of 694. Using the Ar-Ion CW laser, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about 16 %, 11.4 % and 9.6 % for PSL particle size of 2.5 ${\mu}m$, 1.0 ${\mu}m$, and 0.5 ${\mu}m$ respectively at the Reynolds number of 320. Particle beam width was minimized around the laser power of 0.2 W. However, as increasing the laser power higher than 0.4 W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively. On the other hand, using 30 Hz pulsed Nd-YAG laser, the effect of the radiation pressure on the particle beam width was not distinct unlike Ar-Ion CW laser.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.263.1-263.1
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• 2013

탄소나노튜브(CNT)를 이용한 초소형 X선 튜브는 근접 암치료, 비파괴 X선 영상 장치, 휴대용 X선 분광계 등에서 X선 발생소스로 많이 연구되고 있다. 2극형 CNT 에미터의 경우 구조가 단순하여 초소형 X선 튜브에 쉽게 장착할 수 있지만 아노드의 전압과 전류가 연동되기 때문에 튜브의 조작성이 제한적이다. 3극형은 상대적으로 복잡한 구조이고, CNT에서 방출된 전자가 게이트 전극으로 흐르는 누설 전류 그리고 절연체와 충돌하여 차징을 발생시킬 수 있기 때문에 직경이 좁은 초소형 X선 튜브에 구현하기가 쉽지 않다. 하지만 초소형 X선 튜브를 다양한 X선 장치에 응용하기 위해서는 아노드 전압과 전류의 독립된 조작이 가능한 3극형 CNT 에미터가 반드시 구현되어야 한다. 본 발표에서는 전자빔의 아노드 집속을 강화하고 절연체에서의 차징을 줄이는 포커싱 기능의 게이트(FFG) 구조를 제안하였고. 이를 적용하여 초소형 X선 튜브들을 제작하고, 분석하였다. FFG 구조가 성공적으로 적용된 초소형 X선 튜브는 게이트 누설 전류 없이 뛰어난 전류 및 X선 방출 특성을 보였다. 이와는 달리, 몇몇 초소형 X선 튜브들에서는 게이트 누설 전류가 나타났고, 아노드 전압에 의한 게이트 전압 상승이 발생하여 불안정한 구동 특성을 보였다. 초소형 X선 튜브를 밀봉하지 않고 진공 챔버에서 실험한 결과, 유도된 게이트 전압은 상당한 시간이 흐르거나 진공챔버에 공기를 주입하고 다시 진공상태로 만들면 유도전압이 제거되는 것을 볼 수 있었다. 결론적으로 CNT에서 방출된 전자빔이 정상궤도를 벗어나 게이트 누설전류와 차징에 의한 게이트 유도전압을 발생시키면 초소형 X선 튜브가 불안정한 구동을 하고, 결국 튜브의 심각한 결함으로 나타나게 된다. 즉, 게이트 누설 전류와 유도된 게이트 전압은 3극형 CNT 에미터가 장착된 초소형 X선 튜브의 디자인과 제작에 있어서 성공 기준이 될 수 있다.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.450-458
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• 2019

Passive cavitation imaging method is used to observe the ultrasonic waves generated when a group of bubbles collapses. A problem with passive cavitation imaging is a low resolution and large side lobe levels. Since ultrasound signals generated by passive cavitation take the form of a pulse, the amplitude distribution of signals received across the receive channels varies depending on the direction of incidence. Both the centroid and flatness were calculated to determine weights at imaging points in order to discriminate between the main and side lobe signals from the signal amplitude distribution of the received channel data and to reduce the side lobe levels. The centroid quantifies how the channel data are distributed across the receive channel, and the flatness measures the variance of the channel data. We applied the centroid weight and the flatness to the passive cavitation image constructed using the delay-and-sum focusing and minimum variance beamforming methods to improve the image quality. Using computer simulation and experiment, we show that the application of weighting in delay-and-sum and minimum variance beamforming reduces side lobe levels.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.391-401
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• 2004

3D imaging systems using 2D phased arrays have a large number of active channels, compelling to use a very expensive and bulky beamforming hardware, and suffer from low volume rate because, in principle, at least one ultrasound transmit-receive event is necessary to construct each scanline. A high speed 3D imaging method using a cross array proposed previously to solve the above limitations can implement fast scanning and dynamic focusing in the lateral direction but suffer from low resolution except at the fixed transmit focusing along the elevational direction. To overcome these limitations, we propose a new real-time volumetric imaging method using a cross array based on the synthetic aperture technique. In the proposed method, ultrasound wave is transmitted successively using each elements of an 1D transmit array transducer, one at a time, which is placed along the elevational direction and for each firing, the returning pulse echoes are received using all elements of an 1D receive array transducer placed along the lateral direction. On receive, by employing the conventional dynamic focusing and synthetic aperture method along lateral and elevational directions, respectively, ultrasound waves can be focused effectively at all imaging points. In addition, in the proposed method, a volume of interest consisting of any required number of slice images, can be constructed with the same number of transmit-receive steps as the total number of transmit array elements. Computer simulation results show that the proposed method can provide the same and greatly improved resolutions in the lateral and elevational directions, respectively, compared with the 3D imaging method using a cross array based on the conventional fixed focusing. In the accompanying paper, we will also propose a new real-time 3D imaging method using a cross array for improving transmit power and elevational spatial resolution, which uses linear wave fronts on transmit.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1849-1851
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• 1999

The PDP(Plasma Display Panel) barrier rib was fabricated by focused $Ar^+$ laser ($\lambda$=514nm) and Nd:YAG($\lambda$=532, 266 nm) laser irradiation. The depth of the etched groove increases with increasing a laser fluence. and decreasing a scan speed. Using the second harmonic of the Nd:YAG laser, the threshold laser fluence was $6.5mJ/cm^2$ for the sample of PDP barrier rib dried at $120^{\circ}C$. The thickness of $150{\mu}m$ of the sample on the glass was etched without any damage on the glass substrate by fluence of $19.5J/cm^2$. The barrier rib sample on hot plate was etched by Nd:YAG laser(532 nm) as increasing a temperature of the sample. In this case, the etch rate was $95{\mu}m/s$, $190{\mu}m/s$ at room temperature, $175^{\circ}C$ respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.275.1-275.1
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• 2016

반전형 폴리머 태양전지는 그 구조에 의하여 훌륭한 안정성을 가질 뿐만 아니라 roll-to-roll 공정을 통한 대량생산이 가능하여 각광받고 있는 구조이다. 이런 반전형 구조에서, 금속 산화물 나노파티클에 의해 만들어지는 금속 산화물 층은 전자수송층으로서 사용된다. 이 연구에서는 표면개질 물질인 PEIE (Polyethyleneimine-ethoxylate)와 화학적으로 기능화된 산화아연/그래핀 핵/껍질 양자점을 이용하여 전기수송층의 역할을 하는 기능화된 산화아연/그래핀 단분자층을 가지는 태양전지를 제작하였다. 이는 기능화된 산화아연/그래핀 단분자층이 표면개질, 광센서, 전기수송층의 역할을 동시에 수행하는 효과로 인해 제작된 태양전지는 향상된 전자 수집능력을 보였다. 단분자층이 잘 형성되어 있는지 확인하기 위하여 집속 이온 빔 장비를 이용하여 태양전지의 내부 구조를 확인하였으며, density functional theory (DFT)을 이용한 모델링을 통하여 기능화된 산화아연/그래핀 양자점의 전자상태밀도를 분석하였다. 기능화된 산화아연 단분자층에 의한 효과적인 계면 제어 및 전하수송에 의해 약 10.3%의 높은 효율을 가지는 반전형 폴리머 태양전지를 제작할 수 있었다.