• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1994년도 춘계학술대회 논문집
• /
• pp.113-115
• /
• 1994

We considered the ion and photo-induced properties as a function of wavelength by exposing the light over the band gap of a-Ag/a-$Se_{75}$$Ge_{25}$ and the low-energy defocused $Ga^{+}$ ion beam on Ag/a-$Se_{75}$$Ge_{25}$ thin film. This film acts as a negative resist for photo or ion beam lithography. We observed that the absorbance coefficient decreased with increasing the photo-exposing time and exposing the ion beam. The bandgap shifts toward longer wavelength called a "darkening effect" are observed in the films exposed to both photons and ions. We suggest that a primary step in the Ag layer and a secondary step is in a-$Se_{75}$$Ge_{25}$ film layer.

• 공업화학
• /
• 제30권1호
• /
• pp.88-94
• /
• 2019

삼중항-삼중항 소멸에 의한 광에너지 상향전환 기술(triplet-triplet annihilation upconversion, TTA-UC)은 특정 조건을 만족시키는 유기물들의 에너지 전달 및 융합 과정에 의해 저에너지의 광자를 고에너지의 광자로 변환시키는 신개념 에너지 전환기술이다. 본 연구에서는 실리카 마이크로입자(silica microparticle, SM)를 UC가 구현되는 폴리우레탄 박막 내에 담지 시켜 입사되는 광원의 광산란 효과를 도모함으로써 TTA-UC 효율을 향상시키고, 그 기작에 대해 탐구하였다. Seeded growth method를 통하여 약 950 nm의 균일한 크기를 갖는 SM을 합성하였으며, UC 박막 내에 담지 된 SM의 농도를 증가시킴에 따라 635 nm 광원 조사 시 430-570 nm 영역에서의 UC 세기가 최대 1.64배 증가함을 확인하였다. 삼중항 lifetime 측정을 통하여 광감응제 PdTPBP와 전자수용체 perylene 간의 triplet-triplet energy transfer(TTET) 효율을 분석한 결과, 박막 내에 담지 된 SM이 chromophore 간의 TTET에 미치는 영향은 미미한 것으로 나타났다. 또한, 입사 강도-UC 세기의 상관관계를 분석하여 TTA-UC 효율을 분석한 결과, SM이 박막 내에 존재할 경우 UC 양자효율이 최대 1.5배 향상됨을 확인하였다.

• Journal of Radiation Protection and Research
• /
• 제31권4호
• /
• pp.165-171
• /
• 2006

국내에서는 현재 물리적 인형 모의피폭체와 수십 개의 소형 MOSFET 선량계를 이용하여 유효선량(Effective Dose)을 실시간으로 정확하게 측정할 수 있는 시스템을 개발 중에 있다. 이때 사용되는 MOSFET 선량계는 그 크기가 매우 작으며, 상대적으로 높은 민감도를 가지고 선량을 실시간으로 측정할 수 있다는 장점이 있는 반면, 검출부위가 조직등가 물질이 아닌 실리콘으로 이루어져 있어 저에너지 광자에 대하여 적절한 보정이 필요하다. 본 연구에서는 몬테칼로 전산모사 방법을 사용하여 증기발생기 수실 내부의 에너지 스펙트럼에 대한 MOSFET 선량계의 선량보정인자 값들을 계산하였으며, 이렇게 계산된 보정인자 값들을 선행 연구에서 구한 값, 즉 0.662 MeV와 1.25 MeV의 광자만을 이용하여 구한 선량보정인자 값들과 비교하여 보았다. 비교 결과, 두 서로 다른 조건에서의 선량보정인자들은 큰 차이를 보이지 않았으며$(\leq1.5%)$, 따라서 선행 연구에서 구한 선량보정인자들을 원자력발전소의 증기발생기 수실에 그대로 적용하여도 큰 문제가 없음을 알 수 있었다. 또한, 증기발생기 수실에 대하여 결정된 선량보정인자들을 실측된 MOSFET 선량계의 선량값들에 적용하여 선량보정에 따라 유효선량이 어느 정도 변화하는 가를 확인한 결과, 유효선량은 선량보정인자를 적용할 경우가 적용하지 않을 경우에 비해 약 7% 정도 낮게 평가됨을 알 수 있었다.

• Nuclear Engineering and Technology
• /
• 제51권3호
• /
• pp.860-866
• /
• 2019

The lead element or its salts are good radiation shielding materials. However, their toxic effects are high. Due to less toxicity of bismuth salts, the radiation shielding properties of the bismuth salts have been investigated and compared to that of lead salts to establish them as a better alternative to radiation shielding material to the lead element or its salts. The transmission geometry was utilized to measure the mass attenuation coefficient (${\mu}/{\rho}$) of different salts containing lead and bismuth using a high-resolution HPGe detector and different energies (between 81 and 1333 keV) emitted from point sources of $^{133}Ba$, $^{57}Co$, $^{22}Na$, $^{54}Mn$, $^{137}Cs$, and $^{60}Co$. The experimental ${\mu}/{\rho}$ results are compared with the theoretical values obtained through WinXCOM program. The theoretical calculations are in good agreement with their experimental ones. The radiation protection efficiencies, mean free paths, effective atomic numbers and electron densities for the present compounds were determined. The bismuth fluoride ($BiF_3$) is found to have maximum radiation protection efficiency among the selected salts. The results showed that present salts are more effective for reducing the intensity of gamma photons at low energy region.

• Nuclear Engineering and Technology
• /
• 제54권2호
• /
• pp.666-673
• /
• 2022

The optimization of a transmission type bremsstrahlung conversion target was carried out with Monte Carlo code FLUKA for intense pulsed electron beams with electron energy of several hundred keV for maximum photon fluence. The photon emission intensity from electrons with energy ranging from 300 keV to 1 MeV on tungsten, tantalum and molybdenum targets was calculated with varied target thicknesses. The research revealed that higher target material element number and electron energy leads to increased photon fluence. For a certain target material, the target thickness with maximum photon emission fluence exhibits a linear relationship with the electron energy. With certain electron energy and target material, the thickness of the target plays a dominant role in increasing the transmission photon intensity, with small target thickness the photon flux is largely restricted by low energy loss of electrons for photon generation while thick targets may impose extra absorption for the generated photons. The spatial distribution of bremsstrahlung photon density was analyzed and the optimal target thicknesses for maximum bremsstrahlung photon fluence were derived versus electron energy on three target materials for a quick determination of optimal target design.

• Journal of Electrical Engineering and information Science
• /
• 제3권3호
• /
• pp.316-321
• /
• 1998

In recent years, concern has been raised about the technique of controlling electrical breakdown by using laser in many fields. Especially, laser has attracted much attention in the Electro-Discharge Macining(EDM) because of its many merits. Therefore, this research has been performed to obtain fundamental data relevant to discharge processing by using a pulsed Nd:YAG laser. The experiments of laser-guided dc discharge by laser radiation have been carried out at low air pressure ranging from 0.2 to 20 torr. The minimum laser-guided dc discharge voltage V\ulcorner at the given pressures P and distances D between an anode and a cathode was measured. It is found that the minimum laser-guided dc discharge voltage is much lower than the natural discharge voltage V\ulcorner\ulcorner, and the values of V\ulcorner and V\ulcorner as a function of P.D has a similar tendency. The laser output energy Eout decreases with input pulse duration tp increasing, and the more the value of tp increases, the higher that of V\ulcorner is obtained because the number of photons during the discharge time N decreases with t\ulcorner increasing. There is the time lag frequently when the discharge by laser radiation is misguided under the condition of the applied voltage less than V_G.min.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.320-320
• /
• 2014

Amorphous silicon alloy (a-Si) solar cells and modules have been receiving a great deal of attention as a low-cost alternate energy source for large-scale terrestrial applications. Key to the achievement of high-efficiency solar cells using the multi-junction approach is the development of high quality, low band-gap materials which can capture the low-energy photons of the solar spectrum. Several cell designs have been reported in the past where grading or buffer layers have been incorporated at the junction interface to reduce carrier recombination near the junction. We have investigated profiling the composition of the a-SiGe alloy throughout the bulk of the intrinsic material so as to have a built-in electrical field in a substantial portion of the intrinsic material. As a result, the band gap mismatch between a-Si:H and $a-Si_{1-x}Ge_x:H$ creates a barrier for carrier transport. Previous reports have proposed a graded band gap structure in the absorber layer not only effectively increases the short wavelength absorption near the p/i interface, but also enhances the hole transport near the i-n interface. Here, we modulated the GeH4 flow rate to control the band gap to be graded from 1.75 eV (a-Si:H) to 1.55 eV ($a-Si_{1-x}Ge_x:H$). The band structure in the absorber layer thus became like a U-shape in which the lowest band gap was located in the middle of the i-layer. Incorporation of this structure in the middle and top cell of the triple-cell configuration is expected to increase the conversion efficiency further.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.162-162
• /
• 2011

Nanometer-sized noble metals can trap and guide sunlight for enhanced absorption of light based on surface plasmon that is beneficial for generation of hot electron flows. A pulse of high kinetic energy electrons (1-3 eV), or hot electrons, in metals can be generated after surface exposure to external energy, such as in the absorption of light or in exothermic chemical processes. These energetic electrons are not at thermal equilibrium with the metal atoms. It is highly probable that the correlation between hot electron generation and surface plasmon can offer a new guide for energy conversion systems [1-3]. We show that hot electron flow is generated on the modified gold thin film (<10 nm) of metal-semiconductor (TiO2) Schottky diodes by photon absorption, which is amplified by localized surface plasmon resonance. The short-circuit photocurrent obtained with low energy photons (lower than bandgap of TiO2, ~3.1-3.2 eV) is consistent with Fowler's law, confirming the presence of hot electron flows. The morphology of the metal thin film was modified to a connected gold island structure after heating to 120, 160, 200, and 240$^{\circ}C$. These connected island structures exhibit both a significant increase in hot electron flow and a localized surface plasmon with the peak energy at 550-570 nm, which was separately characterized with UV-Vis [4]. The result indicates a strong correlation between the hot electron flow and localized surface plasmon resonance with possible application in hot electron based solar cells and photodetectors.

• Preventive Nutrition and Food Science
• /
• 제9권4호
• /
• pp.317-323
• /
• 2004

Photostimulated Luminescence (PSL), Electron Spin Resonance (ESR) and Thermoluminescence (TL) analysis were conducted to detect irradiation treatment of imported whole and ground spices. The screening by PSL detected no irradiation treatment, except un the ground thyme and bay leaves which exhibited photon counts in the intermediate level. Irradiation of the two spices was detected after irradiating them at 1.0, 3.0, 5.0 and 10.0 kGy, and then subjecting them to PSL analysis, which resulted in the significantly low photons of non-irradiated spices compared to that at 1.0 kGy, indicating that the photon counts varied depending on the amount of inorganic mineral debris in the spices. To confirm a successful detection by using PSL, ESR and TL methods, some spices were selected, irradiated at 5.0 and 10.0 kGy, and subjected to the detection methods. PSL identified the irradiated spices except the cassia, which showed very weak PSL sensitivity, but was identified by ESR analysis. Also, the ESR and TL exhibited the typical signals induced by irradiation treatment and were able to successfully detect all of the irradiated spices. In addition, we found a positive correlation between the intensity of ESR and TL signals and irradiation doses.

• Journal of Radiation Protection and Research
• /
• 제33권2호
• /
• pp.53-59
• /
• 2008

X선과 같은 고에너지 방사선에 의한 DNA 손상 중 간접적인 손상을 확인하기 위하여 탄탈륨(Ta) 박막위에 동결건조 과정으로 만들어진 pGEM-3Zf(-) plasmid DNA 단일층(monolayer)의 박막을 만든 다음, 에너지가 1.5 keV인 Al $K{\alpha}$ X선을 0분, 3분, 7분, 10분 동안 초고진공 상태에서 이 DNA 단일층에 조사하여 평균 흡수선량(mean absorbed dose)의 변화에 따른 DNA 손상을 관찰하였다. 또한 3 eV의 낮은 에너지 전자선을 조사하여 그 결과를 X선을 조사한 경우와 비교하였다. X선과 낮은 에너지 전자선으로 조사된 plasmid DNA를 전기영동(electrophoresis) 방법을 이용해 supercoiled DNA와 unsupercoiled DNA로 분리한 후 각각을 정량적으로 분석하였다. Supercoiled DNA는 X선과 3 eV 전자선의 조사에 따른 평균흡수선량이 증가함에 따라 선형적으로 감소했다. 그와 반대로 circular DNA와 crosslinked form 1 DNA는 평균흡수선량이 증가함에 따라 선형적으로 증가했다. 이것은 supercoiled DNA가 낮은 에너지 전자와 상호작용하여 외가닥 절단(single strand break)을 일으켰고 그 결과 unsupercoiled DNA로 변화되었음을 보여준다. 본 실험을 통해 X선과 같은 고에너지 방사선에 의한 DNA의 간접적 손상이 일어남을 관찰할 수 있었고, DNA의 이온화 에너지보다 작은 에너지($0{\sim}10\;eV$)를 갖는 전자에 의해서도 DNA 손상이 일어날 수 있음을 확인할 수 있었다.