• Nano
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• 제13권10호
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• pp.1850124.1-1850124.12
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• 2018

$TiO_2$ films were deposited from oxygen/titanium tetraisopropoxide (TTIP) plasmas at low temperature by Helicon-PECVD at floating potential ($V_f$) or substrate self-bias of -50 V. The influence of titanium precursor partial pressure on the morphology, nanostructure and optical properties was investigated. Low titanium partial pressure ([TTIP] < 0.013 Pa) was applied by controlling the TTIP flow rate which is introduced by its own vapor pressure, whereas higher titanium partial pressure was formed through increasing the flow rate by using a carrier gas (CG). Then the precursor partial pressures [TTIP+CG] = 0:027 Pa and 0.093 Pa were obtained. At $V_f$, all the films exhibit a columnar structure, but the degree of inhomogeneity is decreased with the precursor partial pressure. Phase transformation from anatase ([TTIP] < 0.013 Pa) to amorphous ([TTIP+CG] = 0:093 Pa) has been evidenced since the $O^+_2$ ion to neutral flux ratio in the plasma was decreased and more carbon contained in the film. However, in the case of -50 V, the related growth rate for different precursor partial pressures is slightly (~15%) decreased. The columnar morphology at [TTIP] < 0.013 Pa has been changed into a granular structure, but still homogeneous columns are observed for [TTIP+CG] = 0:027 Pa and 0.093 Pa. Rutile phase has been generated at [TTIP] < 0:013 Pa. Ellipsometry measurements were performed on the films deposited at -50 V; results show that the precursor addition from low to high levels leads to a decrease in refractive index.

• Current Photovoltaic Research
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• 제7권1호
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• pp.1-8
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• 2019

The $Cu(In,Ga)Se_2$ (CIGS) thin film obtained by two-step process (metal deposition and Se annealing) has a rough surface morphology and many voids at the CIGS/Mo interface. To solve the problem a precursor that contains Se was employer by depositing a (In,Se)/(Cu,Ga) stacked layer. We devised a two-step annealing (vacuum pre-annealing and Se annealing) for the precursor because direct annealing of the precursor in Se environment resulted in the small grains with unwanted demarcation between stacked layers. After vacuum pre-annealing up to $500^{\circ}C$ the CIGS film consisted of CIGS phase and secondary phases including $In_4Se_3$, InSe, and $Cu_9(In,Ga)_4$. The secondary phases were completely converted to CIGS phase by a subsequent Se annealing. A void-free CIGS/Mo interface was obtained by the two-step annealing process. Especially, the CIGS film prepared by vacuum annealing $450^{\circ}C$ and subsequent Se annealing $550^{\circ}C$ showed a densely-packed grains with smooth surface, well-aligned bamboo grains on the top of the film, little voids in the film, and also little voids at the CIGS/Mo interface. The smooth surface enhanced the cell performance due to the increase of shunt resistance.

• Current Photovoltaic Research
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• 제10권2호
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• pp.39-48
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• 2022

A Se-containing Cu/SnSe₂/ZnSe precursor was employed to introduce S to the precursor to form Cu₂ZnSn(S,Se)₄ (CZTSSe) film. The morphology of CZTSSe films strongly varied with two different pre-annealing environments: S and N₂. The CZTSSe film with S pre-annealing showed a dense morphology with a smooth surface, while that with N₂ pre-annealing showed a porous film with a plate-shaped grains on the surface. CuS and Cu₂Sn(S,Se)₃ phases formed during the S pre-annealing stage, while SnSe and Cu₂SnSe₃ phases formed during the N₂ pre-annealing stage. The SnSe phase formed during N₂ pre-annealing generated SnS₂ phase that had plate shape and severely aggravated the morphology of CZTSSe film. The power conversion efficiency of the CZTSSe solar cell with S pre-annealing was low (1.9%) due to existence of Zn(S.Se) layer between CZTSSe and Mo substrate. The results indicated that S pre-annealing of the precursor was a promising method to achieve a good morphology for large area application.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2003년도 생물공학의 동향(XII)
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• pp.34-38
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• 2003

For the production of $B^{30}-homoserine$ insulin analog as a novel anti-diabetic drug, the fermentative study was attempted for the maximal gene expression of HTS-fused $B^{30}-homoserine$ insulin precursor in the recombinant Escherichia coli cells. In a batch fermentation, the maximal production of insulin precursor as much as 38.95 mg/L-h, which occupied more than 12.8% of total cell protein. was achieved when the gene expression was induced by 0.5 mM IPTG at the middle logarithmic growth phase. The HTS-fused $B^{30}-homoserine$ insulin precursor was recovered from a batch culture through the processes of cell harvest, collection of insoluble fraction after sonication and purification by nickel affinity column chromatography. The isolated insulin precursor was 14 mg/L with a recovery yield of 35.9% of expressed gene product. The insulin A and B chain mixture was recovered after the insulin precursor was subjected to CNBr cleavage and purified by nickel affinity column chromatography. The isolated insulin chains were then sulfitolyzed with sodium thiosulfat and sodium tetrathionate, and reconstituted to insulin analog with ${\beta}-mercaptoethanol$, followed by purification with CM-Sepharose C-25 column chromatography.

• 한국연소학회지
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• 제9권2호
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• pp.38-44
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling, were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories, C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth process). These results provide a clear picture of a transition to mature soot from precursor materials.

• 대한화학회지
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• 제59권3호
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• pp.238-245
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• 2015

The crystallization and morphology change of amorphous titanias by hydrothermal treatment have been investigated. The amorphous titanias were prepared by pure water hydrolysis of two different precursors, titanium tetraisopropoxide (TTIP) and TTIP modified with acetic acid (HOAc) and characterized prior to hydrothermal treatment. In order to avoid complicate situation, the hydrothermal treatment was performed in a single solvent water with and without strong acids at various temperatures. The effects of strong acid, temperature and time were systematically investigated on the transformation of amorphous titania to crystalline TiO₂ under simple hydrothermal condition. Without strong acid the titanias were transformed into only anatase phase nanoparticle regardless of precursor type, temperature and time herein used (up to 250 ℃ and 48 hours). The treatment temperature and time effected only on the crystalline size, not on the crystal phase et al. However, it was clearly revealed that the strong acids such as HNO₃ and HCl catalyzed the formation of rutile phase depending on temperature. HCl was slightly better than HNO₃ in this catalytic activity. The morphology of rutile TiO₂ formed was also a little affected by the type of acid. The precursor modifier, HOAc slightly reduced the catalytic activity of the strong acids in rutile phase formation.

• 한국세라믹학회지
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• 제27권7호
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• pp.934-942
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• 1990

The quarternary system ceramics 0.5[yPb(Zn1/3Nb2/3)O3-(1-y)Pb(Ni1/3Nb2/3)O3]-0.5[xPbTiO3-(1-x)PbZrO3](PZN-PNN-PT-PZ) was fabricated by the columbite precursor method to obtain a stabilized perovskite structure and by conventional method to evaluate the efficiency of the former methd. Dielectric and piezoelectric properties were investigated and the stability of the perovskite phase was studied as a function of PZN and PT contents and firing temperature. In the samples prepared by the columbite precursor method, the pyrochlore phase, which is detrimental to both the dielectric and piezoelectric properties, was not observed in the absence of PZN, and electric properties were improved even when fabricated at low temperature. By adding PZN, some pyrochlore phase appeared and the morphotropic phase boundary of the samples shifted to more Zr-rich composition. The temperature dependence of piezoelectric constant decreased with the addition of PZN, due to the rising of the Curie point.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.42-43
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• 2006

High Tc superconducting with a BiSrCaCuO was prepared by the citrate method. The solid precursor produced by the dehydration of the gel at $120^{\circ}C$ for 12h is not in the a morphous state as expected but in a crystalline state. X -ray diffraction peaks of nearly the same angular position as the peaks of high Tc phase were observed in the precursor.

• The Korean Journal of Ceramics
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• 제5권3호
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• pp.239-244
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• 1999

Ultrafine lead magnesium niobate $Pb(Mg_{1/3}Nb_{2/3}) O_3$ (PMN) powders have been successfully prepared via a micro-emulsion processing technique. By stepwise hydrolysis using aqueous as the precipitant, hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a microemulsion consisting of cyclohexane, non-ionic surfactant (NP5+NP9) and an aueous phase. Upon calcination of the microemulsion-derived precursor at $800^{\circ}C$, PMN powders with 100% perovskite phase was obtained.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2001년도 High Temperature Superconductivity Vol.XI
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• pp.52-52
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• 2001