• Carbon letters
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• 제15권2호
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• pp.129-135
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• 2014

Spinnable pitch for melt-electrospinning was obtained from pyrolized fuel oil by electron beam (E-beam) radiation treatment. The modified pitch was characterized by measuring its elemental composition, softening point, viscosity, molecular weight, and spinnability. The softening point and viscosity properties of the modified pitch were influenced by reforming types (heat or E-beam radiation treatment) and the use of a catalyst. The softening point and molecular weight were increased in proportion to absorbed doses of E-beam radiation and added $AlCl_3$ due to the formation of pitch by free radical polymerization. The range of the molecular weight distribution of the modified pitch becomes narrow with better spinning owing to the generated aromatic compounds with similar molecular weight. The diameter of melt-electrospun pitch fibers under applied power of 20 kV decreased 53% ($4.7{\pm}0.9{\mu}m$) compared to that of melt-spun pitch fibers ($10.2{\pm}2.8{\mu}m$). It is found that E-beam treatment for reforming could be a promising method in terms of time-savings and cost-effectiveness, and the melt-electrospinning method is suitable for the preparation of thinner fibers than those obtained with the conventional melt-spinning method.

• Journal of Advanced Marine Engineering and Technology
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• 제29권3호
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• pp.313-318
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• 2005

Li-doped ZnS layers were grown by molecular beam epitaxy. It was found that relatively low growth temperature is suitable for effective incorporation of Li acceptors. The layers grown under optimized conditions exhibited photoluminescence spectra dominated by neutral-acceptor-bound excitons. Such layers also showed electrically p-type behavior in capacitance-voltage characteristics. The net acceptor concentration is estimated to be approximately $3{\times}10^{15}\;cm^{-3}$.

• 방사선산업학회지
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• 제7권1호
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• pp.51-54
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• 2013

Chitosan is a useful natural polymer material in many application fields such as biomaterials, water-treatment, agriculture, medication, and food science. However, the poor solubility limits its application. In this study, the effects of radiation on chitosan were investigated using gamma ray and electron beam irradiation. The chemical structure and molecular weight analysis show similar degradation effects of chitosan powder in both gamma ray and electron beam irradiation. However, the radiation irradiated chitosan in $H_2O$ has a lower molecular weight, since the hydroxyl radicals attack the glycosidic bonds. This effect is more clearly shown in the electron beam irradiation results.

• 한국결정성장학회지
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• 제17권2호
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• pp.52-56
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• 2007

본 연구에서는 초고진공(UHV, ultra high vacuum) 분자선 에피성장(MBE, molecular beam epitaxy) 시스템을 제작하여, ZnSe/GaAs[001]을 증착하였고, 증착된 박막의 특성을 SEM(scanning electron microscopy), AFM(atomic force microscopy)으로 조사하여, 분자층 단위의 조밀하고 균일한 표면특성을 보이고 있음을 확인할 수 있었다 XRD(x-ray diffractometer)를 이용하여, GaAs[001]기판의 XRD peak 위치와 ZnSe 박막의 XRD peak 위치가 각자 일치함을 확인할 수 있었다. PL(photoluminescence)로는 대략 437nm에서 발광하는 것이 관측되었으며, 2인치 ZnSe 박막의 PL mapping을 측정하였다.

• 한국재료학회지
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• 제9권1호
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• pp.25-29
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• 1999

We have developed a laser molecular beam epitaxy system for the layer-by-layer growth of oxide thin films. Using this system, we could grow and control oxide thin films of LaAlO$_3$in a molecular layer epitaxy mode on the atomically flat SrTiO$_3$ substrate with a LaAlO$_3$single crystal target. Very clear RHEED oscillations were observed during to growth of a LaAlO$_3$ film for a long period under the optimized conditions of substrate temperature at $650^{\circ}C$, oxygen pressure at 1$\times$10\ulcorner torr, and an incident laser fluence of 4.6J/$\textrm{cm}^2$. The height of mono-layer-LaAlO$_3$ film grown during one period of RHEED intensity oscillation was 3.8$\AA$.

• 한국결정성장학회지
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• 제9권1호
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• pp.1-5
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• 1999

Molecular beam epitaxy법으로 $CaF_{2}$ (111) 기판위에 희토류 이온 ($(Nd^{3+},\;Er^{3+})$) 첨가 $CaF_{2}$ 박막을 성장하였다. 첨가농도와 박막두께에 따른 희토류 첨가 $CaF_{2}$ 박막의 표면구조와 결정성을 RHEED로 검토하였다. 반도체 관련 고집적회로구조에 있어서의 완층막으로서의 응용을 고려하여, 희토류첨가 $CaF_{2}$ 박막과 $CaF_{2}$ (111) 기판과의 격자부정합의 변이를 X-ray rocking Curve 분석에 의해 검토하였다.

• 한국진공학회지
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• 제15권5호
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• pp.458-464
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• 2006

본 연구에서는 초고진공 (UHV; ultra high vacuum) 분자선 에피성장 (MBE; molecular beam epitaxy) 시스템의 제작과 성능연구가 성공적으로 이루어졌다. 초고진공 용 분자선 에피성장 시스템을 국산화개발 및 제작하여, 장비에 관한 성능 테스트를 하게 되었다. 본 장비의 진공도가 $2X10^{10}$ Torr에 도달함을 확인하였고, 시편 가열모듈(substrate heating module)이 $1,100^{\circ}C$까지 가열됨을 확인할 수 있었으며, ZnSe/GaAs(001)의 증착특성을 SEM (scanning electron microscope), AFM (atomic force microscope), XRD (x-ray diffraction), PL (photoluminescence) 등으로 조사하였다.

• 한국표면공학회지
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• 제43권4호
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• pp.170-175
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• 2010

The GaAs epitaxial layers were grown on Si(100) substrates by molecular beam epitaxy(MBE) using the two-step method. The Si(100) substrates were cleaned with different surface cleaning method of vacuum heating, As-beam, and Ga-beam at the substrate temperature of $800^{\circ}C$. Growth temperature and thickness of the GaAs epitaxial layer were $800^{\circ}C$ and 1 ${\mu}m$, respectively. The surface structure and epitaxial growth were observed by reflection high-energy electron diffraction(RHEED) and scanning electron microscope(SEM). Just surface structure of the Si(100) substrate cleaned by Ga-beam at $800^{\circ}C$ shows double domain ($2{\times}1$). RHEED patterns of the GaAs epitaxial layers grown on Si(100) substrates with cleaning method of vacuum heating, As-beam, and Ga-beam show spot-like, ($2{\times}4$) with spot, and clear ($2{\times}4$). From SEM, it is found that the GaAs epitaxial layers grown on Si(100) substrates with Ga-beam cleaning has a high quality.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.238-243
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• 1995

A pulsed molecular beam source having short pulse duration (typically 70 ${\mu}s)$ and narrow velocity distribution (${\Delta}$v/v=8% for helium) has been costructed utilizing a commercial fuel injector. Beam characteristics of helium and ammonia seeded in helium expansions are accomplished by the use of an electron impact time-or-flight mass spectrometer. The comparisons between experimental data and theoretical calculations show that the proper beam speed is important to predict the evolution of stream temperature and valve shutter function. The decreasing tendency of pulse duration with increasing cluster size leads to the conclusion that the cluster beam property is described as a function of cluster mass and disinct cluster temperature.

• Carbon letters
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• 제15권4호
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• pp.262-267
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• 2014

Pyrolized fuel oil (PFO) was reformed by novel electron beam (E-beam) radiation, and the elemental composition, chemical bonds, average molecular weight, solubility, softening point, yields, and density of the modified patches were characterized. These properties of modified pitch were dependent on the reforming method (heat or E-beam radiation treatment) and absorbed dose. Aromaticity ($F_a$), average molecular weight, solubility, softening point, and density increased in proportion to the absorbed dose of E-beam radiation, with the exception of the highest absorbed dose, due to modification by free radical polymerization and the powerful energy intensity of E-beam treatment. The H/C ratio and yield exhibited the opposite trend for the same reason. These results indicate that novel E-beam radiation reforming is suitable for the preparation of aromatic pitch with a high ${\beta}$-resin content.