• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2089-2092
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• 2007

Tantalum-containing metal oxides, well known for their efficiency in water splitting and H2 production, have never been used in visible light driven photodecomposition of H2S and H2 production. The present work is an attempt in this direction and investigates their efficiency. A mixed metal oxide, ZnFe2Ta2O9, with the inclusion of Fe2O3 to impart color, was prepared by the conventional ceramic route in single- and double-calcinations (represented as ZnFe2Ta2O9-SC and ZnFe2Ta2O9-DC respectively). The XRD characterization shows that both have identical patterns and reveals tetragonal structure to a major extent and a minor contribution of orthorhombic crystalline system. The UV-visible diffuse reflection spectra demonstrate the intense, coherent and wide absorption of visible light by both the catalysts, with absorption edge at 650 nm, giving rise to a band gap of 1.9 eV. Between the two catalysts, however, ZnFe2Ta2O9-DC has greater absorption in almost the entire wavelength region, which accounts for its strong brown coloration than ZnFe2Ta2O9-SC when viewed by the naked eye. In photocatalysis, both catalysts decompose H2S under visible light irradiation (λ ≥ 420 nm) and produce solar H2 at a much higher rate than previously reported catalysts. Nevertheless, ZnFe2Ta2O9-DC distinguishes itself from ZnFe2Ta2O9-SC by exhibiting a higher efficiency because of its greater light absorption. Altogether, the tantalum-containing mixed metal oxide proves its efficient catalytic role in H2S decomposition and H2 production process also.

• 한국자기학회지
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• 제16권2호
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• pp.140-143
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• 2006

단결정 상태의 $CoFe_2O_4$ 박막을 rf magnetron sputtering 증착법을 이용하여 (100) MgO 기판 위에 성장시켰다. X선 회절기, Rutherford back-scattering 분석기와 고감도 주사전자현미경을 이용하여 측정한 결과 증착된 박막이 기판과 잘 정렬되어 성장한 것을 확인할 수 있었다. $600^{\circ}C$의 기판 온도에서 성장한 페라이트 박막은 약 200nm크기의 사각형 형태로 규칙적으로 분포되어 있음이 관찰되었다. 그러나 $700^{\circ}C$의 기판 온도에서 성장한 박막은 불규칙한 모양으로 이루어져 있었으며 30nm에서 150nm에 이르는 다양한 입자 크기를 보이고 있었다. 섭동자화기를 이용한 자기이력곡선 측정 결과 성장한 박막의 자화용이축이 기판과 수직하게 배열하는 것을 알 수 있었다. 또한 MgO 기판과 성장 박막과의 격자상수 차이로 인하여 기판과 수직한 방향의 보자력은 매우 큰 값을 나타내었다. 즉 평행한 방향의 보자력은 283 Oe이고 수직한 방향의 보자력은 6800 Oe였다. $700^{\circ}C$의 기판 온도에 서 성장한 페라이트 박막은 $600^{\circ}C$의 기판 온도에서 성장한 박막의 보자력 및 포화자화 값과 유사한 값을 보였으나 각형비는 급격하게 감소하였다.

• 한국재료학회지
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• 제3권2호
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• pp.175-184
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• 1993

Nd-Fe-B계에 Co와 Al을 첨가한 자석합금을 진공유도용해로에서 제조하여 이들 합금을 단롤법으로 melt-spun시켜 급냉리본을 얻었다. 제작된 급냉리본의 냉각속도에 따른 자기적 성질의 변화를 조사하였고, 최적의 급냉속도에서 제작된 리본을 파쇄하여 resin bond 자석을 제조하였으며, 이들 급냉리본 및 bond자석의 자기적 성질, 미세구조, 결정구조에 관하여 연구, 조사하였다. 이들 급냉리본의 자기적 성질은 급냉속도에 따라 크게 변하였으며 20m/sec전후에서 최적의 자기적 성질을 보였다. 이때의 급냉리본의 미세조직은 Nd-rich의 입계상이 미세한 N$d_2$F$e_14$B결정립을 둘러싼 cell 형의 구조였으며, 특히 Al이 2.1at%첨가된 리본시료에서는 iHc=15.5KOe, Br=7.8KG, (BH)max=8.5MGOe의 자기적 성질을 나타내었다. 최적의 급냉속도에서 제작된 리본을 polyamide resin과 2.5wt%의 비율로 혼합하여 상온에서 성형, 결합시켜 제작한 bond자석에서 보다 현저히 향상되었으며 유지시간이 8분인 경우 iHc=10.8KOe, Br=7.3KG, (BH)max=8.0MGOe의 값을 가졌다. 한편, 자구구조는 maze pattern이 주로 관찰되어 자화용이축인 C축이 배열되었으며 bond자석에서보다 hot-press 자석에서 자구폭이 보다 작았다.

• Applied Biological Chemistry
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• 제26권2호
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• pp.137-142
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• 1983

한국산 고구마의 두 품종, 수원 147 호와 천미의 전분을 분리하여 전분입자의 성상과 이화학적 특성을 조사 검토하였다. 광학현미경과 scanning electron microscopy로 관찰한 고구마 전분은 둥근형과 다각형이었으며, 그 크기는 수원 147 호가 $14{\sim}30{\mu}m$, 천미가 $16{\sim}34{\mu}m$이었다. X-선회절도는 $2{\theta}$가 14.8, 17.2, 22.5에서 약한 결정성을 보이므로 실험한 고구마 전분은 Ca결정형으로 생각된다. Blue value는 수원 147호가 0.342, 천미가 0.279, 아밀로즈 함량은 27.6%, 23.6%, 물결합 능력은 178.7%, 185.5%이었다. 전분의 팽화력은 $50^{\circ}C$까지는 변화가없다가 그후 급격히 증가하였으며 수원 147호가 천미보다 완만한 증가를 보였다. 전분 현탁액(0.2%)의 광투과도는 두 전분 모두 $65^{\circ}C$부터 급격히 증가하였고 $65{\sim}80^{\circ}C$까지 single stage의 호화 양상을 보였다. 아밀로 그라프에 의한 4% 전분 용액의 호화는 모두 최고 점도가 나타나지 않았으며 $92.5^{\circ}C$에서 수원 147호의 점도는 증가하였으나 천미 전분의 점도는 감소하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.289-289
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• 2013

While there are plenty of studies on synthesizing semiconducting germanium nanowires (Ge NWs) by vapor-liquid-solid (VLS) process, it is difficult to inject dopants into them with uniform dopants distribution due to vapor-solid (VS) deposition. In particular, as precursors and dopants such as germane ($GeH_4$), phosphine ($PH_3$) or diborane ($B_2H_6$) incorporate through sidewall of nanowire, it is hard to obtain the structural and electrical uniformity of Ge NWs. Moreover, the drastic tapered structure of Ge NWs is observed when it is synthesized at high temperature over $400^{\circ}C$ because of excessive VS deposition. In 2006, Emanuel Tutuc et al. demonstrated Ge NW pn junction using p-type shell as depleted layer. However, it could not be prevented from undesirable VS deposition and it still kept the tapered structures of Ge NWs as a result. Herein, we adopt $C_2H_2$ gas in order to passivate Ge NWs with carbon sheath, which makes the entire Ge NWs uniform at even higher temperature over $450^{\circ}C$. We can also synthesize non-tapered and uniformly doped Ge NWs, restricting incorporation of excess germanium on the surface. The Ge NWs with carbon sheath are grown via VLS process on a $Si/SiO_2$ substrate coated 2 nm Au film. Thin Au film is thermally evaporated on a $Si/SiO_2$ substrate. The NW is grown flowing $GeH_4$, HCl, $C_2H_2$ and PH3 for n-type, $B_2H_6$ for p-type at a total pressure of 15 Torr and temperatures of $480{\sim}500^{\circ}C$. Scanning electron microscopy (SEM) reveals clear surface of the Ge NWs synthesized at $500^{\circ}C$. Raman spectroscopy peaked at about ~300 $cm^{-1}$ indicates it is comprised of single crystalline germanium in the core of Ge NWs and it is proved to be covered by thin amorphous carbon by two peaks of 1330 $cm^{-1}$ (D-band) and 1590 $cm^{-1}$ (G-band). Furthermore, the electrical performances of Ge NWs doped with boron and phosphorus are measured by field effect transistor (FET) and they shows typical curves of p-type and n-type FET. It is expected to have general potentials for development of logic devices and solar cells using p-type and n-type Ge NWs with carbon sheath.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.131-131
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• 2013

A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly(methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with interrupted growth studies to reconstruct ex-situ the heating process. The data clearly show that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for vaporizing hydrocarbon molecules from PMMA and the length of time the gaseous hydrocarbon atmosphere is maintained, which are dependent on both the heating temperature profile and the amount of a solid carbon feedstock are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ~2,700 cm2V-1s-1 at room temperature, superior to common graphene converted from solid carbon.

• 한국재료학회지
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• 제22권7호
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• pp.346-351
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• 2012

$Li_{1+x}Al_xTi_{2-x}(PO_4)_3$(LATP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this study, LATP is prepared through a sol-gel method using relatively the inexpensive reagents $TiCl_4$. The thermal behavior, structural characteristics, fractured surface morphology, ion conductivity, and activation energy of the LATP sintered bodies are investigated by TG-DTA, X-ray diffraction, FE-SEM, and by an impedance method. A gelation powder was calcined at $500^{\circ}C$. A single crystalline phase of the $LiTi_2(PO_4)_3$(LTP) system was obtained at a calcination temperature above $650^{\circ}C$. The obtained powder was pelletized and sintered at $900^{\circ}C$ and $1000^{\circ}C$. The LTP sintered at $900{\sim}1000^{\circ}C$ for 6 h had a relatively low apparent density of 75~80%. The LATP(x = 0.3) pellet sintered at $900^{\circ}C$ for 6 h was denser than those sintered under other conditions and showed the highest ion conductivity of $4.50{\times}10^{-5}$ S/cm at room temperature. However, the ion conductivity of LATP (x = 0.3) sintered at $1000^{\circ}C$ decreased to $1.81{\times}10^{-5}$ S/cm, leading to Li volatilization and abnormal grain growth. For LATP sintered at $900^{\circ}C$ for 6 h, x = 0.3 shows the lowest activation energy of 0.42 eV in the temperature range of room temperature to $300^{\circ}C$.

• 한국재료학회지
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• 제21권11호
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• pp.634-638
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• 2011

We report growth of epitaxial AlN thin films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. To achieve two-dimensional growth the substrates were nitrided by nitrogen plasma prior to the AlN growth, which resulted in the formation of a two-dimensional single crystalline AlN layer. The formation of the two-dimensional AlN layer by the nitridation process was confirmed by the observation of streaky reflection high energy electron diffraction (RHEED) patterns. The growth of AlN thin films was performed on the nitrided AlN layer by changing the Al beam flux with the fixed nitrogen flux at 860$^{\circ}C$. The growth mode of AlN films was also affected by the beam flux. By increasing the Al beam flux, two-dimensional growth of AlN films was favored, and a very flat surface with a root mean square roughness of 0.196 nm (for the 2 ${\mu}m$ ${\times}$ 2 ${\mu}m$ area) was obtained. Interestingly, additional diffraction lines were observed for the two-dimensionally grown AlN films, which were probably caused by the Al adlayer, which was similar to a report of Ga adlayer in the two-dimensional growth of GaN. Al droplets were observed in the sample grown with a higher Al beam flux after cooling to room temperature, which resulted from the excessive Al flux.

• 방사선산업학회지
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• 제4권3호
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• pp.221-226
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• 2010

Physical detection methods, photostimulated luminescence (PSL), thermoluminescence (TL) and electron spin resonance (ESR) were applied to detect electron beam-irradiated agricultural products, such as red pepper, black pepper, raisin, walnut, beef seasoning and pistachio. The absorbed irradiation doses for representative samples were controled at 0, 1, 3, 5 and 10 kGy. PSL values for non-irradiated samples were <700 counts/60s (lower threshold, $T_1$) except beef seasoning, whereas those of irradiated samples were more than 5,000 photon counts, upper threshold ($T_2$) in black pepper, raisin, and beef seasoning and intermediates values of $T_1-T_2$ in red pepper, walnut, and pistachio. Minerals seperated from the samples for TL measurement showed that non-irradiated samples except pistachio (TL ratio, 0.12) were characterized by no glow curves situated at temperature range of $50{\sim}400^{\circ}C$ with TL ratio (0.01~0.08), while irradiated samples except pistachio at only 1 kGy (TL ratio, 0.08) indicated glow curve at about $150{\sim}250^{\circ}C$ with TL ratio (0.28~3.10). ESR measurements of irradiated samples showed any specific signals to irradiation. The samples of both red pepper and pistachio were produced specific signals derived from cellulose radicals as well as single line signals for black pepper and walnut, and multiple signals derived from crystalline sugar radicals for raisin and beef seasoning. In conclusion, The ESR methods can apply for detection of pistachio exposed to electron beam but PSL and TL are not suitable methods. Furthermore, TL and ESR suggeted that both techniques were more useful detection method than PSL to confirm whether red pepper, walnut and beef seasoning samples have been exposed to electron beam.

• 구강회복응용과학지
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• 제37권3호
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• pp.111-122
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• 2021

목적: 5Y-ZP의 세가지 층 간 굽힘강도, 투과도를 비교하고 추가적인 소성이 미치는 영향을 연구하고자 하였다. 연구 재료 및 방법: 소결한 지르코니아 블록을 세가지 층에 따라 분리한 후 원형 디스크 시편을 제작하였다. 시편의 직경은 15.0 mm이며, 2축굽힘강도와 투과도를 측정하기 위한 시편의 두께는 각각 1.2 mm와 1.0 mm이다. 시편들을 추가적인 소성 횟수(0, 1, 3번)에 따라 세 군으로 분류한 후 추가적인 소성은 900℃ 이하의 온도에서 퍼니스를 사용하여 소성 횟수에 따라 시행하였다. 만능재료시험기와 자외선-가시광선 분광광도계를 사용하여 2축굽힘강도와 투과도를 측정하였다. 상의 변화를 관찰하기 위해 X선 회절 분석을 시행하였다. 측정값은 One-way ANOVA, Tukey HSD test를 통하여 분석하였다(α = 0.05). 결과: 층 간 2축굽힘강도는 유의한 차이가 없었지만(P > 0.05) 투과도는 유의한 차이가 있었다(P < 0.05). 절단 및 전이층은 1번의 추가적인 소성 후 굽힘강도가 유의하게 감소하였으며, 3번의 추가적인 소성 후에는 모든 층의 굽힘강도가 소성 전과 비교하여 유의하게 감소하였다. 몸체 층을 제외한 나머지 층들은 추가적인 소성 후에 투과도가 유의하게 감소하였다. 모든 그룹의 X선 회절 분석 결과는 유사하였다. 결론: 5Y-ZP의 세 층은 투과도의 차이만 존재하였다. 추가적인 소성은 각 층의 굽힘강도와 투과도에 다른 영향을 미쳤으나 상전이는 발견되지 않았다.