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여러 질소 플라즈마 상태에서 성장한 wurtzite GaN의 결정특성
조성환(Sung Hwan Cho),김순구(Soon Koo Kim),유연봉(Yeon Bong Yoo) 한국진공학회(ASCT) 1997 Applied Science and Convergence Technology Vol.6 No.4
다양한 질소 압력, 플라즈마 파워 상태에서 사파이어 기판위에 전자 사이클로트론 공명 MBE로 제작한 wurtzite GaN의 결정특성을 XRD의 반치폭, 주사전자 현미경으로 조사하였다. 질소 압력은 XRD의 반치폭에 커다란 영향을 미치고 있으며 최적 질소 압력에서 제작한 시료에는 높은 dislocation density를 포함하고 있슴을 알았다. 이러한 결과들은 갈륨질소의 결정질(crystal quality)은 플라즈마 상태에 매우 민감하며 또한 스트레스 완화는 V/Ⅲ 비에 의존하고 있음을 나타낸다. 그렇지만 사파이어 기판의 nitridation은 스트레스 완화에 커다란 영향을 미치지 않고 있었다. Crystal properties of wurtzite GaN films grown on Al₂O₃(0001) substrates under various nitrogen pressure and plasma power by electron cyclotron resonance molecular beam epitaxy were investigated by full width at half maximum of X-ray diffraction peak and scanning electron microscope. It was found that the nitrogen pressure has a large effect on the FWHM value of XRD, and the GaN film grown under the optimum nitrogen pressure contains high density of dislocations. These results suggest that the crystal quality is sensitive to the plasma source conditions and that the relaxation of stress depends on V/Ⅲ ratio. However, substrate-surface nitridation has little effect on the relaxation of misfit stress.
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W/Si 및 WNx/Si Schottkey 다이오우드의 전기적 특성
劉演奉 三陟大學校 1995 論文集 Vol.28 No.2
The electrical properties of the W/Si and WNx/Si Schottkey contacts deposited by plasma enhanced chemical vapor deposition technique were investigated. We measured leakage current at 5V reverse bias for W/Si, WNx/Si diodes fabricated with various reactant gases. The leakage current for WNx/Si diode deposited with WF6-NH3-H2 gas system has the lowest value of all. As-deposited tungsten film was a polycrystal consisting of only (110), (200), and (211) oriented α-W phase, similarly in the case of the tungsten films deposited on silicon by plasma enhanced chemical vapor deposition. And, as-deposited WNx film NH3/WF6=0.5 ratio shows a amorphous structure slightly consisting of α-W and metastable β-W phases. Then the thermal stability and elctrical property of the WNx/Si samples were compared with the W/Si samples by Ⅰ-V, XRD, SEM measurements. It is evident that the thermal stability of the WNx/Si diodes is excellent than the W/Si diodes. We then measured leakage current after annealing at reverse applied voltage. The leakage current for W/Si diode increased with annealing at 900℃ for 20sec, but that for WNx/Si diode decreased slightly at 900℃. Therefore, it is thought that WNx is stble during high temperature annealing above about 800℃ because the tungsten-silicide is not performed at WNx/Si interface.
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劉演奉 三陟大學校 1995 論文集 Vol.28 No.2
The thermal stability of the photoluminescence and Raman spectra of various thermally treated porous silicon samples have been investigated. Samples were prepared by electrochemially etching silicon wafers with a current density of 50mA/㎠ in an HF, DI water solution for 10 min and then post-annealing them under various conditions. Porous silicon samples which underwent rapid thermal oxidization and further annealing in a N2 ambient were compared with those which were only rapid thermal annealed. Anealing of as-prepared porous silicon in an inert gas atmosphere shows a severe degradation in the photoluminescence intensity 500℃, whereas, the photoluminescence of the pre-oxidized samples shows thermal stability. Oxidation of the sample is believed to cause of this stability.
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Cation이 Europium, Praseodymium인 Nitroprusside [Fe(CN)?NO]² 분말내의 중심 원자인 철에 대한 M?ssbauer parameters
劉演奉 삼척대학교 1997 論文集 Vol.30 No.3
We observed the ?Fe Mossbauer spectra for the ground states at room temperature of sodium nitroprusside. Na₂[Fe(CN)?NO]·2H₂O single crystal. europium notroprusside. Eu₂[Fe(CN)?NO]₃·9H₂O powder. praeseodymuim nitropruside and Pr₂[Fe(CN)?NO]₃·6H₂O powder which is substituted cations as rare earth metal element. The M??ssbauer parameters. isomer shifts (I.S.). quadrupole splittings (Q.S.) and full width half maxima (F.W.H.M.T.) of the ground state in two powder samples are compared with ground state of sodium nitroprusside single crystal for analysis of the electronic properties of the materials. We have found that values of quadrupole splitting for ground state in two powder samples are positive larger than these parameter in sodium nitroprusside single crystal and values of ?????? shifts of these for ground state in there samples are equal within experimental errors.
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劉演奉 三陟大學校 1999 論文集 Vol.32 No.3
To estimate the thermal annealing effect of the nuclear reactor pressure vessel (RPV) by the fast neutron (En>1MeV) irradiation, we have studied the change of the Mossbauer parameters of RPV steel with the fast neutrons dosage of 1, ??, ?? n/㎠. DSC experiment was done to find annealing temperature of all samples, so all samples were annealed at 600℃ for 1, 2, 3 and 4 hours respectively. The influence of neutron irradiation on RPV steel was studied by Mossbauer effect. The Mossbauer spectra for all samples showed the superposition of two sextets and one doublet at room temperature. The isomer shift(I. S.) and quadrupole splitting(Q. S.) values of sextets were changed within experimental errors for all samples, but these values of doublet were rapidly changed at the sample of the dose ?? n/㎠. The magnetic hyperfine field was varied within ±3%. For thermal annealing, we can not found any particular change in the values of I.S. and Q. S. But in Geff. we think that there were any annealing effect for the dose 1016 n/㎠ after 3 hours annealing time.
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이용곤,김형상,홍치유,유연봉 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-
The embrittlement of fast neutron-irradiated reactor pressure vessel (RPV) steels was investigated by X-ray diffraction patterns at room temperature and Mo¨ssbauer spectroscopy at room- and liquid nitrogen-temperature. Neutron fluence on the samples were 1012, 1013, 1014, 1015, 1016, 1017, 1018n/cm². The X-ray diffraction patterns at room temperature showed that the structure of neutron unirradiated sample was bcc type, where as but the neutron irradiated samples with the fluence higher than 1017 n/cm² were so severely damaged, that bcc type structure disappeared. The Mo¨ssbauer spectra of all samples showed superposition of two or more sextets. In this paper all Mo¨ssbauer spectra were fitted by three set of sextet. The isomer shift and quadrupole splitting values were found around zero. At liquid nitrogen temperature, magnetic hyperfine field increase rapidly to 480 ∼ 552 kOe at S1 sextet in the samples of 1017∼1018n/cm² neutron fluences. And room temperature, magnetic hyperfine field also increased rapidly to 480 ∼507 kOe at S1 sextet in the samples of 1017∼1018n/cm²neutron fluences. This rapid increase of magnetic hyperfine field was infered to be caused by the change of 56Fe, 55Mn into 57Fe by neutron irradiation.
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