• 제목/요약/키워드: Photon density

검색결과 235건 처리시간 0.024초

Optically Controlled Silicon MESFET Modeling Considering Diffusion Process

  • Chattopadhyay, S.N.;Motoyama, N.;Rudra, A.;Sharma, A.;Sriram, S.;Overton, C.B.;Pandey, P.
    • JSTS:Journal of Semiconductor Technology and Science
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    • 제7권3호
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    • pp.196-208
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    • 2007
  • An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

일년생과 다년생 식물의 경합에 미치는 인산의 효과 (The Efect of Phosphorus on Competition in Annual and Perennial Plants)

  • 정찬;전병태
    • 한국초지조사료학회지
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    • 제12권1호
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    • pp.1-5
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    • 1992
  • 자연군락에 인산비과를 시용하여 토양용액중의 인산농도를 높일 경우, 일년생 및 다년생식물의 초장, 건물량의 반응성을 조사하였다. 또한, Italian ryegrass를 자연군락중에 파종하여, 그 후의 정착과 성장에 미치는 인산비과의 영향을 조사함으로서 일년생식물과 다년생식물과의 경쟁관계에 미치는 토양중 인산 농도의 영향을 검토하였다. 다년생식물인 MIscanthus, SaSa 및 Artemisia군락에서는 초장, 건물량에 대한 인산 시비의 효과는 작었지만, 일년생식물인 Polygonum 및 Echinochloa군락에서는 효과가 크게 나타났다. 각 자연군락내의 Italian ryegrass의 초장, 밀도 및 지상부 건물량은 토양의 전인산과 유효태 인산 수준에 크게 의존하였고, 군락중 상대광양자밀도에는 의존도가 낮았다.

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극초단 펄스 레이저에 의한 절연체의 광학 손상 해석 (Numerical Analysis of Optical Damage in Dielectrics Irradiated by Ultra-Short Pulsed Lasers)

  • 이성혁;강관구;이준식;최영기;박승호;유홍선
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.1213-1218
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    • 2004
  • The present article reports extensive numerical results on the non-local characteristics of ultra-short pulsed laser-induced breakdowns of fused silica ($SiO_{2}$) by using the multivariate Fokker-Planck equation. The nonlocal type of multivariate Fokker-Planck equation is modeled on the basis of the Boltzmann transport formalism to describe the ultra-short pulsed laser-induced damage phenomena in the energy-position space, together with avalanche ionization, three-body recombination, and multiphoton ionization. Effects of electron avalanche, recombination, and multiphoton ionization on the electronic transport are examined. From the results, it is observed that the recombination becomes prominent and contributes to reduce substantially the rate of increase in electron number density when the electron density exceeds a certain threshold. With very intense laser irradiation, a strong absorption of laser energy takes place and an initially transparent solid is converted to a metallic state, well known as laser-induced breakdown. It is also found that full ionization is provided at intensities above threshold, all further laser energy is deposited within a thin skin depth.

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극초단펄스 레이저에 의한 크롬박막 미세가공 (Ablation of Cr Thin Film on Glass Using Ultrashort Pulse Laser)

  • 김재구;신보성;장원석;최지연;장정원
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2003년도 춘계학술대회 논문집
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    • pp.620-623
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    • 2003
  • The material processing by using ultrashort pulse laser, in recently, is actively applying into the micro machining and nano-machining technology since ultrashort pulse has so faster than the time which the electrons energy absorbing photon energy is transmitted to surrounding lattice-phonon that it has many advantages in point of machining. The micro machining of metallic thin film on the plain glass is widely used in the fields such as mask repairing for semiconductor, fabrication of photonic crystal, MEMS devices and data storage devices. Therefore, it is important to secure the machining technology of the sub-micron size. In this research, we set up the machining system by using ultrashort pulse laser and conduct on the Cr 200nm thin film ablation experiments of spot and line with the variables such as energy, pulse number, speed, and so on. And we observed the characteristics of surrounding heat-affected zone and by-products appeared in critical energy density and higher energy density through SEM, and also examined the machining features between in He gas atmosphere which make pulse change minimized by nonlinear effect and in the air. Finally, the pit size of 0.8${\mu}{\textrm}{m}$ diameter and the line width of 1${\mu}{\textrm}{m}$ could be obtained.

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High-Efficiency Dye-Sensitized Solar Cells by Extended Spectral Response Utilizing Dye Selective Positioning Method

  • 이도권;박세웅
    • 한국재료학회:학술대회논문집
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    • 한국재료학회 2010년도 춘계학술발표대회
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    • pp.12.1-12.1
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    • 2010
  • We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO2 layer through selective desorption and adsorption processes. Only upper part of the first adsorbed N719 dye was selectively removed by the desorption solution formulated with polypropylene glycol and tetrabutylammonium hydroxide without any damages of the dye. The desorption depth was controlled by the number of desorption process. Multi-dyed dye-sensitized solar cells (MDSSC) were fabricated by utilizing the method and their photovoltaic properties were investigated. From the incident photon-to-current conversion efficiency (IPCE) measurement, it was found that the MDSSC exhibited the extended spectral response for the solar spectrum while without decrease of maximum IPCE value compare to the DSSCs using one kind of dye (N719 or N749). The highest photocurrent density of 19.3 mA/cm2 was obtained from the MDSSC utilizing $15\;{\mu}m$ N719 / $14\;{\mu}m$ N749 bi-layered mesoporous TiO2 film. The photocurrent density was 25% and 8% higher than that of the DSSC using only N719 and N749 dye as a sensitizer, respectively. The power conversion efficiency of 9.8% was achieved from the MDSSC under the AM 1.5G one sun illumination.

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STARS: A 3D GRID-BASED MONTE CARLO CODE FOR RADIATIVE TRANSFER THROUGH RAMAN AND RAYLEIGH SCATTERING WITH ATOMIC HYDROGEN

  • Chang, Seok-Jun;Lee, Hee-Won
    • 천문학회지
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    • 제53권6호
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    • pp.169-179
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    • 2020
  • Emission features formed through Raman scattering with atomic hydrogen provide unique and crucial information to probe the distribution and kinematics of a thick neutral region illuminated by a strong far-ultraviolet radiation source. We introduce a new 3-dimensional Monte-Carlo code in order to describe the radiative transfer of line photons that are subject to Raman and Rayleigh scattering with atomic hydrogen. In our Sejong Radiative Transfer through Raman and Rayleigh Scattering (STaRS) code, the position, direction, wavelength, and polarization of each photon is traced until escape. The thick neutral scattering region is divided into multiple cells with each cell being characterized by its velocity and density, which ensures flexibility of the code in analyzing Raman-scattered features formed in a neutral region with complicated kinematics and density distribution. To test the code, we revisit the formation of Balmer wings through Raman scattering of the far-UV continuum near Lyβ and Lyγ in a static neutral region. An additional check is made to investigate Raman scattering of O vi in an expanding neutral medium. We find a good agreement of our results with previous works, demonstrating the capability of dealing with radiative transfer modeling that can be applied to spectropolarimetric imaging observations of various objects including symbiotic stars, young planetary nebulae, and active galactic nuclei.

양극산화로 제조된 다공성 나노구조 철 산화막의 열처리 조건에 따른 광전기화학적 성질 (Photoelectrochemical performance of anodized nanoporous iron oxide based on annealing conditions)

  • 정동헌;유정은;이기영
    • 한국표면공학회지
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    • 제56권4호
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    • pp.265-272
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    • 2023
  • Photoelectrochemical (PEC) water splitting is one of the promising methods for hydrogen production by solar energy. Iron oxide has been effectively investigated as a photoelectrode material for PEC water splitting due to its intrinsic property such as short minority carrier diffusion length. However, iron oxide has a low PEC efficiency owing to a high recombination rate between photoexcited electrons and holes. In this study, we synthesized nanoporous structured iron oxide by anodization to overcome the drawbacks and to increase surface area. The anodized iron oxide was annealed in Ar atmosphere with different purging times. In conclusion, the highest current density of 0.032 mA/cm2 at 1.23 V vs. RHE was obtained with 60 s of pursing for iron oxide(Fe-60), which was 3 times higher in photocurrent density compared to iron oxide annealed with 600 s of pursing(Fe-600). The resistances and donor densities were also evaluated for all the anodized iron oxide by electrochemical impedance spectra and Mott-Schottky plot analysis.

Evaluating polyester resin as a viable substitute for PMMA in computed tomography dosimetry phantoms

  • A. Khallouqi;A. Halimi;O. El rhazouani
    • Nuclear Engineering and Technology
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    • 제56권9호
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    • pp.3758-3763
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    • 2024
  • The current study aimed to evaluate the suitability of polyester resin as an alternative material to polymethyl methacrylate (PMMA) for computed tomography (CT) dosimetry phantoms using the GEANT4/GATE Monte Carlo simulation platform. Cylindrical phantoms (32 cm diameter) constructed of polyester resin and PMMA were simulated and compared in terms of atomic composition, effective atomic number, electron density, mass density, and photon interaction mechanisms. Weighted CT dose index (CTDIw) values were calculated for each phantom at 80, 110, and 130 kVp tube voltages based on measurements of CTDI100,c and CTDI100,p. Results demonstrated that the physical properties of polyester closely matched those of PMMA, and the polyester phantom displayed equivalent dosimetric behavior to the PMMA phantom at all tube voltages tested. CTDIw values from the polyester phantom were within 1.4 % of the PMMA phantom across all tube voltages. Conversion coefficients were derived to equate polyester CTDIw values to PMMA dose equivalents. This study found that a polyester resin phantom exhibited radiation dosimetry commensurate with the standard PMMA phantom for CT dose assessment. Consequently, polyester resin represents a viable substitute material when PMMA is unavailable for construction of CT dosimetry phantoms.

쐐기필터 사용 시 레디오크로믹 필름을 이용한 조직에 따른 선량분포 연구 (Dose Distribution According to the Tissue Composition Using Wedge Filter by Radiochromic Film)

  • 김연래;이정우;박병문;정재용;박지연;서태석
    • 대한방사선기술학회지:방사선기술과학
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    • 제35권2호
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    • pp.157-164
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    • 2012
  • 본 논문의 목적은 쐐기필터를 사용한 방사선조사면에서 다양한 조직전자밀도가 선량분포에 미치는 영향을 분석하고자 함이다. 구성된 물질에 따라 밀도가 다른 고체 팬텀, 코르크팬텀, 그리고 공기층에서 동적쐐기필터와 금속쐐기필터를 이용하여 선량분포의 변형정도를 평가하였다. 본 실험에서는 매질 내 삽입이 용이하고 우수한 선량특성을 가지고 있는 레디오크로믹 필름(Gafchromic EBT2, International Speciality Products, NJ)을 사용하였다. 선형가속기 6 MV 광자선을 이용해서 $10{\times}10cm^2$ 조사면에 400 MU를 조사하였다. 필름의 선량분포는 선량 분석프로그램을 이용하여 조사면 내 영역과 반음영 영역을 분석하였다. 조직의 밀도가 같을 때 동적쐐기필터와 금속 쐐기필터의 선량분포는 금속 쐐기필터 선량이 동적쐐기필터 선량보다 높게 나타났다. 조직전자밀도가 다른 부위에 쐐기필터의 종류에 따른 선량분포는 고체팬텀과 코르크 팬텀에서 2% 이내 차이를 나타내고 있었다. 그러나 공기층에서 선량분포는 고체팬텀이나 코르크 팬텀의 선량분포와 큰 차이를 보이고 있다. 공기층에서 쐐기필터의 선량분포는 쐐기 사용 효과가 나타나지 않고 있다. 쐐기필터의 두꺼운 부분과 얇은 부분 밖에서 반음영의 크기는 1 cm에서 2 cm 정도 크게 두꺼운 부분에서 크게 나타났다. 그리고 금속 쐐기필터에서 반음영이 동적쐐기필터 보다 평균 6.4%정도 높게 반음영이 나타났다. 본 실험을 통해 공기층과 같이 조직전자밀도 현저히 작은 매질에서는 쐐기필터의 효과가 크게 떨어지는 것과 불균질 물질에 따라 흡수되는 선량분포가 크게 변형되는 것을 알 수 있었다. 따라서 조직전자밀도의 차이가 큰 부위의 방사선치료계획 시 쐐기필터의 적용에 따른 적절한 보정이 이루어져야 한다.

폐경전 무월경 여성에 있어서 골밀도 측정에 관한 연구 (Bone Mineral Density in Premenopausal Amenorrheic Women with Hypogonadism)

  • 박기현;이병석;이보연;조동제;송찬호
    • Clinical and Experimental Reproductive Medicine
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    • 제19권1호
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    • pp.49-56
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    • 1992
  • Bone mineral density was measured to assess whether the patients with premonopausal hypogonadism, comprised of 19 patients with hypogonadotropic hypogonadism(HH), 55 with premature ovarian failure(POF), 23 with hyperprolactinemia(HPLN), and 8 with Sheehan's syndrome. All aged from 20 to 39, were associated with some decrease in regional bone mass compared with that of 63 normal-associated with some decrease in regional bone mass compared with that of 63 normal-cycling control women matched with age and sex. Measurement of bone mineral density was carried out using Dual photon absorptiometry at four sites; femur neck, ward's triangle, trochanter and spine(L2-L4). Bone mineral density at all four sites were significantly decreased in patients with HH(p<0.01), POF(p<0.01). In hyperprolactinemic patients, the decrease in bone mass was significant at femur neck and Ward's triangle(p<0.05). The patients with POF were noted to be associated with significant bone loss when their duration of amenorrhea exceeded one year. In this study, the degree of loss of bone mass and the affected sites seemed to be different depending on the various types of hypogonadism and POF was noted have caused the appearance of loss of bone mass earlier than other thpes of hypogondism we experienced.

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