• 전자통신동향분석
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• 제34권5호
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• pp.1-13
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• 2019

In modern times, X-ray imaging has become a necessary tool for early diagnosis, quality control, nondestructive testing, and security screening. X-ray imaging equipment generally comprises an X-ray generator and an image sensor. Most commercially available X-ray generators employ filament-thermionic electron-based X-ray tubes, thus demonstrating typical analog behavior, such as slow response and large stray X-rays. Furthermore, digital X-ray sources, which have been studied extensively using field electron emitters manufactured from nanometer-scale materials, provide fast and accurately controlled ultra-shot X-rays. This could usher in a new era of X-ray imaging in medical diagnosis and nondestructive inspections. Specifically, digital X-ray sources, with reduced X-ray dose, can significantly improve the temporal and spatial resolution of fluoroscopy and computed tomography. Recently, digital X-ray tube technologies based on carbon nanotubes, developed by Electronics and Telecommunications Research Institute, have been transferred to several companies and commercialized for dental imaging for the first time.

• 한국재료학회지
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• 제29권1호
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• pp.59-64
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• 2019

This study investigates the optical characteristics of InGaN multiple quantum wells(MQWs) light emitting diodes(LEDs) on planar sapphire substrates(PSSs), nano-sized PSS(NPSS) and micro-sized PSS(MPSS). We obtain the results as the patterning size of the sapphire substrates approach the nanometer scale: The light from the back side of the device increases and the total light extraction becomes larger than the MPSS- and planar-LEDs. The experiment is conducted by Monte Carlo ray-tracing, which is regarded as one of the most suitable ways to simulate light propagation in LEDs. The results show fine consistency between simulation and measurement of the samples with different sized patterned substrates. Notably, light from the back side becomes larger in the NPSS LEDs. We strongly propose that the increase in the light intensity of NPSS LEDs is due to an abnormal optical distribution, which indicates an increase of extraction probability through NPSS.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2277-2288
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• 2021

To regulate the safety protocols in nuclear facilities, radioactive aerosols have been extensively researched to understand their health impacts. However, most measured particle-size distributions remain at low resolutions, with the particle sizes ranging from nanometer to micrometer. This study combines the high-resolution detection of 500 size classes, ranging from 6 nm to 10 ㎛, for aerodynamic diameter distributions, with a regional lung deposition calculation. We applied the new approach to characterize particle-size distributions of aerosols generated during the plasma arc cutting of simulated non-radioactive steel alloy wastes. The high-resolution measured data were used to calculate the deposition ratios of the aerosols in different lung regions. The deposition ratios in the alveolar sacs contained the dominant particle sizes ranging from 0.01 to 0.1 ㎛. We determined the distribution of various metals using different vapor pressures of the alloying components and analyzed the uncertainties of lung deposition calculations using the low-resolution aerodynamic diameter data simultaneously. In high-resolution data, the changes in aerosols that can penetrate the blood system were better captured, correcting their potential risks by a maximum of 42%. The combined calculations can aid the enhancement of high-resolution measuring equipment to effectively manage radiation safety in nuclear facilities.

• 열처리공학회지
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• 제34권6호
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• pp.265-271
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• 2021

In this study, anti-tarnishing and corrosion characteristics of a single 𝛽1' and Bangjja Yugi alloy in the Cl^- ion environment before and after potentiostatic electrolysis treatment were compared. Stable and uniform SnO₂ oxide film with several nanometer thickness is formed after potentiostatic electrolysis treatment. In the case of Bangjja Yugi prior to potentiostatic electrolysis (PE) treatment for exposure in Cl^- environment, tarnishing occurs rapidly within 0.5hr, whereas PE treated Bangjja Yugi indicates stable surface without tarnishing up to 3hr. Especially, it is noticeable that anti-tarnishing and corrosion characteristic of PE treated single 𝛽1', which were significantly improved by 3 times and 15 times, respectively, compared to conventional Bangja Yugi.

• Membrane and Water Treatment
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• 제13권6호
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• pp.313-320
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• 2022

Theoretical calculation results are presented for the enhancement of the water mass flow rate through the hydrophobic micro/nano pores in the membrane respectively on the micrometer and nanometer scales. The water-pore wall interfacial slippage is considered. When the pore diameter is critically low (less than 1.82nm), the water flow in the nanopore is non-continuum and described by the nanoscale flow equation; Otherwise, the water flow is essentially multiscale consisting of both the adsorbed boundary layer flow and the intermediate continuum water flow, and it is described by the multiscale flow equation. For no wall slippage, the calculated water flow rate through the pore is very close to the classical hydrodynamic theory calculation if the pore diameter (d) is larger than 1.0nm, however it is considerably smaller than the conventional calculation if d is less than 1.0nm because of the non-continuum effect of the water film. When the driving power loss on the pore is larger than the critical value, the wall slippage occurs, and it results in the different scales of the enhancement of the water flow rate through the pore which are strongly dependent on both the pore diameter and the driving power loss on the pore. Both the pressure drop and the critical power loss on the pore for starting the wall slippage are also strongly dependent on the pore diameter.

• Membrane and Water Treatment
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• 제14권3호
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• pp.107-114
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• 2023

Graphene oxide (GO) membranes have attracted extensive attention in water treatment and related fields. However, GO films are unstable and have low permeability, which have hindered their further development. In this paper, a simple and effective method was used in which GO and single-layer graphene (GN) were mixed, and the layer spacing was effectively controlled by accurately controlling the ratio of GO to GN. GO-GN composite membranes have excellent stability, salt rejection (95.4%), and water flux (26 L m^-2 h^-1 bar^-1). This unique design structure can be used for precise and effective regulation of the layer spacing in GO, improving the rejection rate, and increasing water flux via the enhancement of low-friction capillary action. The rational development and use of this unique composite membrane provides a reference for the water treatment field.

• Journal of Korean Vacuum Science & Technology
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• 제6권3호
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• pp.133-138
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• 2002

The growth of Au films grown on a Si(100)-2x1 surface and Si films on a Ge(100)-2x1 substrate is studied using Positron-annihilation induced Auger Electron Spectroscopy(PAES), Electron induced Auger Electron Spectroscopy(EAES), and Low Energy Electron Diffraction(LEED). Previous work has shown that PAES is almost exclusively sensitive to the top-most atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. This surface specificity is exploited to profile the surface atomic concentrations during the growth of Au on Si(100) and Si on Ge(100) and EAES provides concentrations averaged over the top 3-10 atomic layers simultaneously. The difference in the probe-depth makes us possible to use PAES and EAES in a complementary fashion to estimate the surface and near surface concentration profiles. The results show that (i) the intermixing of Au and Si atoms occurs during the room temperature deposition, (ii) the segregated Ge layer is observed onto the Si layers deposited at 300k. In addition, the prior adsorption of hydrogen prevents the segregation of Ge on top of the deposited Si and that the hydrogen adsorption is useful in growing a thermally stable structure.

• 한국재료학회지
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• 제34권2호
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• pp.105-110
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• 2024

Scanning probe microscopy (SPM) has become an indispensable tool in efforts to develop the next generation of nanoelectronic devices, given its achievable nanometer spatial resolution and highly versatile ability to measure a variety of properties. Recently a new scanning probe microscope was developed to overcome the tip degradation problem of the classic SPM. The main advantage of this new method, called Reverse tip sample (RTS) SPM, is that a single tip can be replaced by a chip containing hundreds to thousands of tips. Generally for use in RTS SPM, pyramid-shaped diamond tips are made by molding on a silicon substrate. Combining RTS SPM with Scanning spreading resistance microscopy (SSRM) using the diamond tip offers the potential to perform 3D profiling of semiconductor materials. However, damage frequently occurs to the completed tips because of the complex manufacturing process. In this work, we design, fabricate, and evaluate an RTS tip chip prototype to simplify the complex manufacturing process, prevent tip damage, and shorten manufacturing time.

• 폴리머
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• 제32권4호
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• pp.334-339
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• 2008

최근 전기방사공정은 다양한 고분자의 마이크로 및 나노 크기 섬유를 만드는 기술로서 널리 사용되어 왔다. 일반적으로 많은 연구자들에 의하면, 다중노즐 전기방사공정은 노즐들 사이의 전기장 간섭효과 때문에 짧은 시간에 높은 생산성을 갖기 어려웠다. 이러한 문제를 극복하기 위하여 본 연구에서는 다양한 보조전극을 이용한 다중노즐 전기방사공정을 개발하였다. 본 연구에서 사용된 물질은 바이오소재로서 많이 사용되고 있는 poly($\varepsilon$-carprolactone)(PCL)을 사용하였다. 다중노즐 시스템의 영향을 확인하기 위하여 전기방사의 안정성, 다중노즐을 사용하였을 때의 생산성 및 제조된 나노섬유의 크기와 안정성을 보조전극을 사용하였을 때와 사용하지 않았을 때를 비교하였다. 결과적으로 보조전극을 사용한 노즐의 안정성이 사용하지 않은 노즐에 비해 전기방사 안정성과 우수한 생산성을 보였다.

• 한국태양에너지학회 논문집
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• 제32권spc3호
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• pp.213-219
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• 2012

Nanofluids are advanced concept fluid that solid particles of nanometer size are stably dispersed in fluid likes water, ethylene glycol and others. They have higher thermal conductivities than base fluids. If using this characteristic, efficiencies of heat exchangers can be increased. Therefore in this study, we measured thermal conductivity and viscosity of carbon nanofluids. They were made to ultra sonic dispersed oxidized multi-walled carbon nanotubes(OMWCNTs) in distilled water and ethanol, respectively. The mixture ratios of OMWCNTs were from 0.0005 vol% ~ 0.1 vol%. Thermal conductivity and viscosity was measured by transient hot-wire method and rotational viscometer. The results of an experiment are as in the following: thermal conductivity of the 0.1 vol% pure-water nanofluid improved 7.98% ($10^{\circ}C$), 8.34% ($25^{\circ}C$), and 9.14% ($70^{\circ}C$), and its viscosity increased by 37.08% ($10^{\circ}C$), 33.96% ($25^{\circ}C$) and 21.64% ($70^{\circ}C$) than the base fluids. Thermal conductivity of the 0.1 vol% ethanol nanofluids improved 33.72% ($10^{\circ}C$), 33.14% ($25^{\circ}C$), and 32.25% ($70^{\circ}C$), and its viscosity increased by 35.12% ($10^{\circ}C$), 32.01% ($25^{\circ}C$) and 19.12% ($70^{\circ}C$) than the base fluids.