• 제목/요약/키워드: Metal dispersion

검색결과 267건 처리시간 0.035초

GaAs Metal-Semiconductor Field-Effect Transistor에서 표면 결함이 소자의 전달컨덕턴스 분산 및 게이트 표면 누설 전류에 미치는 영향 (Effects of Surface States on the Transconductance Dispersion and Gate Leakage Current in GaAs Metal - Semiconductor Field-Effect Transistor)

  • 최경진;이종람
    • 대한전자공학회논문지SD
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    • 제38권10호
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    • pp.678-686
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    • 2001
  • CaAs metal semiconductor field effect transistor (MESFET) 소자의 전달컨덕턴스 분산 (transconductance dispersion) 현상과 게이트 누설 전류의 원인을 capacitance deep level transient spectroscopy (DLTS) 측정을 이용하여 해석하였다. DLTS 스펙트럼에서는 활성화 에너지가 각각 0.65×0.07 eV와 0.88 × 0.04 eV인 두개의 표면 결함과 0.84 × 0.01 eV의 활성화 에너지를 갖는 EL2를 관찰하였다. 전달컨덕턴스 분산 측정 결과, 전달컨덕턴스는 5.5 Hz ∼ 300 Hz의 주파수 영역에서 감소하였다. 전달컨덕턴스 분산을 온도의 함수로 측정한 결과, 온도가 증가할수록 전이 주파수는 증가하였고 전이 주파수의 온도 의존성으로부터 0.66 ∼ 0.02 eV의 활성화 에너지를 구할 수 있었다. 게이트 누설 전류 측정에서는 0.15 V 이하의 게이트 전압에서 순 방향과 역 방향 게이트 전압이 일치하는 오믹 전류-전압 특성을 나타내었고 게이트 누설 전류의 온도 의존성으로부터 구한 활성화 에너지는 0.63 ∼ 0.01 eV로 계산되었다. 서로 다른 방법으로 구한 활성화 에너지의 비교로부터 표면 결함 H1이 주파수에 따라서 감소하는 전달컨덕턴스 분산 및 게이트 누설 전류의 원인임을 알 수 있었다.

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공기 및 수소 분위기에서 열처리 된 Pt/Al2O3 촉매의 HI분해반응 특성 (The Characteristics of HI Decomposition using Pt/Al2O3 Catalyst Heat Treated in Air and Hydrogen Atmosphere)

  • 박은정;고윤기;박주식;김창희;강경수;조원철;정성욱;배기광;김영호
    • 한국수소및신에너지학회논문집
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    • 제25권3호
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    • pp.219-226
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    • 2014
  • In HI decomposition, $Pt/Al_2O_3$ has been studied by several researchers. However, after HI decomposition, it could be seen that metal dispersion of $Pt/Al_2O_3$ was greatly decreased. This reason was expected of platinum loss and sintering, which platinum was aggregated. Also, this decrease of metal dispersion caused catalytic deactivation. This study was conducted to find the condition to minimize platinum sintering and loss. In particular, heat treatment atmosphere and temperature were examined to improve the activity of HI decomposition reaction. First of all, although $Pt/Al_2O_3$ treated in hydrogen atmosphere had low platinum dispersion between 13 and 18%, it was shown to suitable platinum form that played an important role in improving HI decomposition reaction. Oxygen in the air atmosphere made $Pt/Al_2O_3$ have high platinum dispersion even 61.52% at $500^{\circ}C$. Therefore, in order to get high platinum dispersion and suitable platinum form in HI decomposition reaction, air heat treatment at $500^{\circ}C$ was needed to add before hydrogen heat treatment. In case of 5A3H, it had 51.13% platinum dispersion and improved HI decomposition reaction activity. Also, after HI decomposition reaction it had considerable platinum dispersion of 23.89%.

Helical Compounds Forming Gas-Phase Dimers: A Dispersion-corrected Density Functional Investigation

  • Tongying, Pornthip;Sooksimuang, Thanasat;Tantirungrotechai, Yuthana
    • Bulletin of the Korean Chemical Society
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    • 제32권4호
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    • pp.1231-1236
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    • 2011
  • Chiral discrimination is the ability to distinguish one enantiomeric form over another. The differential binding interaction between two molecules with the same helicity and those with the opposite helicity was investigated by using dispersion-corrected density functional theory. [5]helicene, tetrahydro[5]helicene and the polar D-${\pi}$-A compounds, 3,12-dimethoxy-7,8-dicyano-[5]helicene and 3,12-dimethoxy-7,8-dicyano-tetrahydro[5]helicene were the monomers considered in this study. In gas phase, the dimeric interaction from two helical molecules with the opposite handedness is greater than from those with the same handedness. The stable configurations of such dimers were identified. The most stable configuration tends to be the one with maximum contact between monomers.

압전체를 이용한 약품 분사용 초음파 분사노즐 시스템 (Ultrasonic Spray Nozzle System with Piezoelectric Device for Chemicals Dispersion)

  • 고재석;김용현;최승철
    • 한국마이크로전자및패키징학회:학술대회논문집
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    • 한국마이크로전자및패키징학회 2003년도 기술심포지움 논문집
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    • pp.278-281
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    • 2003
  • A new type of ultrasonic spray nozzle was fabricated with piezoelectric devices. The spray nozzle was designed for the chemicals dispersion in the water purification bath. The piezoelectric properties in ultrasonic spray nozzles were optimized for the better dispersion of chemicals for purification process. Ultrasonic spray nozzle was packaged in metal case with silicone resin for the water proof application.

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분산중합 변수가 폴리메틸메타크릴레이트의 입자크기에 미치는 영향 (Effect of Parameters on the Particle Size in Dispersion Polymerization of Poly(methy1 methacrylate))

  • 김수진;우종표
    • 한국응용과학기술학회지
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    • 제17권4호
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    • pp.257-261
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    • 2000
  • Monodisperse polymer particles have many industrial applications such as surface coatings for metal panels, chromatographic media, spacers for liquid crystal display panel, and fillers for cosmetics, etc.. Micron-size monodispersed poly(methyl methacrylate) particles were prepared by dispersion polymerization in methanol medium in the presence of poly(vinyl pyrrolidone) and 2,2'-azobis(isobutyronitrile) as steric stabilizer and initiator, respectively. Effects of polymerization parameters, such as monomer and initiator concentration, stabilizer type and concentration, solvent composition on average particle size and size distribution were studied.

Investigation of heating and accretion event of Milky Way disk

  • Lee, Ayeon;Lee, Young Sun;Kim, Young Kwang
    • 천문학회보
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    • 제46권2호
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    • pp.67.2-67.2
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    • 2021
  • We present preliminary results on the chemical and kinematic analysis of accreted and heated metal-rich (-1.0 < [Fe/H] < -0.3) stars in the Galactic disk. These stars are in the ranges of e > 0.7, -100 < V𝜙 < 100 km/s, and |Z| < 3 kpc, and are presumably heated (accreted) by (from) past merger events such as Gaia Enceladus and Sausage (GSE). These stars are largely separated into two groups based on the level of [α/Fe] and radial velocity dispersion. The first group has low [α/Fe] and high radial velocity dispersion, and the second group shows high [α/Fe] and low radial velocity dispersion. We propose that the first group of stars are accreted from the GSE galaxy, whereas the second group of stars are dynamically heated by the GSE merger event.

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Synthesis and Characterization of Metal (Pt, Pd and Fe)-graphene Composites

  • Chen, Ming-Liang;Park, Chong-Yeon;Choi, Jong-Geun;Oh, Won-Chun
    • 한국세라믹학회지
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    • 제48권2호
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    • pp.147-151
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    • 2011
  • In this study, we prepared graphene by using the modified Hummers-Offeman method and then introduced the metals (Pt, Pd and Fe) for dispersion on the surface of the graphene for synthesis of metal-graphene composites. The characterization of the prepared graphene and metal-graphene composites was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM). According to the results, it can be observed that the prepared graphene consists of thin stacked flakes of shapes having a well-defined multilayered structure at the edge. And the metal particles are dispersed uniformly on the surface of the graphene with an average particle size of 20 nm.

충북지역 폐금속광산 주변 토양오염도 평가

  • 정명채;강만희;지한구;황범순;박정구;정현석
    • 한국지하수토양환경학회:학술대회논문집
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    • 한국지하수토양환경학회 2005년도 총회 및 춘계학술발표회
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    • pp.24-27
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    • 2005
  • This study has focused on investigation on As and heavy metal contamination derived from metalliferous mining activities in the Choongbuk Province in Korea. Soil, mine effluent, surface water and ground water samples were taken in and around 27 abandoned metal mines, and analyzed for As, Cd, Cu, Ni, Pb and Zn using AAS and anions in water samples using IC. In general, the heavy metal concentrations in soils decreased with Increasing distance from the each mine audit. Tailings and mine waste soils from several mines contained over the guideline of Soil Conservation Act in Korea. Soil samples from the Seobo, Honga, Daehwa, Jeungjadong, Youngbo and Munbaek mines contained over the action levels of the metals due to intensive mining activities. Therefore, a proper remediation work needs to control the metal dispersion around the mines.

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Polytetrafluoroethylene 분말 현탁액을 통한 다공성 박막 제조 및 에너지 발생소자 응용 (Fabrication of Porous Polytetrafluoroethylene thin Film from Powder Dispersion-solution for Energy Nanogenerator Applications)

  • 박일규
    • 한국분말재료학회지
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    • 제24권2호
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    • pp.102-107
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    • 2017
  • Porous polytetrafluoroethylene (PTFE) thin films are fabricated by spin-coating using a dispersion solution containing PTFE powders, and their crystalline properties are investigated after thermal annealing at various temperatures ranging from 300 to $500^{\circ}C$. Before thermal annealing, the film is densely packed and consists of many granular particles 200-300 nm in diameter. However, after thermal annealing, the film contains many voids and fibrous grains on the surface. In addition, the film thickness decreases after thermal annealing owing to evaporation of the surfactant, binder, and solvent composing the PTFE dispersion solution. The film thickness is systematically controlled from 2 to $6.5{\mu}m$ by decreasing the spin speed from 1,500 to 500 rpm. A triboelectric nanogenerator is fabricated by spin-coating PTFE thin films onto polished Cu foils, where they act as an active layer to convert mechanical energy to electrical energy. A triboelectric nanogenerator consisting of a PTFE layer and Al metal foil pair shows typical output characteristics, exhibiting positive and negative peaks during applied strain and relief cycles due to charging and discharging of electrical charge carriers. Further, the voltage and current outputs increase with increasing strain cycle owing to accumulation of electrical charge carriers during charge-discharge.

Waves dispersion in an imperfect functionally graded beam resting on visco-Pasternak foundation

  • Saeed I. Tahir;Abdelbaki Chikh;Ismail M. Mudhaffar;Abdelouahed Tounsi;Mohammed A. Al-Osta
    • Geomechanics and Engineering
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    • 제33권3호
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    • pp.271-277
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    • 2023
  • This article investigates the effect of viscoelastic foundations on the waves' dispersion in a beam made of ceramic-metal functionally graded material (FGM) with microstructural defects. The beam is considered to be shear deformable, and a simple three-unknown sinusoidal integral higher-order shear deformation beam theory is applied to represent the beam's displacement field. Novel to this study is the investigation of the impact of viscosity damping on imperfect FG beams, utilizing a few-unknowns theory. The stresses and strains are obtained using the two-dimensional elasticity relations of FGM, neglecting the normal strain in the beam's depth direction. The variational operation is employed to define the dispersion relations of the FGM beam. The influences of the material gradation exponent, the beam's thickness, the porosity, and visco-Pasternak foundation parameters are represented. Results showed that phase velocity was inversely proportional to the damping and porosity of the beams. Additionally, the foundation viscous damping had a stronger influence on wave velocity when porosity volume fractions were low.