• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.81-86
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• 2001

We have investigated surface photovoltage characteristics of InGaAs grown by metalorganic chemical vapor deposition (MOCVD) method on semi-insulating GaAs. The splitted SPV signals from the substrate and epilayer were observed. The band gap energy of InGaAs was about 1.376 eV, The In composition(x) was determined by Pan's composition formula. The photovoltage gradually decreases with increasing frequency. This is because the transfer of charge from the surface states reduces. From the temperature dependent SPV measurement, we obtained Varshni and temperature coefficients. In spectrum of etched sample at 300 K, the 'A' peak below $E_o(GaAs)$ is related with residual impurity during sample growth.

• Journal of Electrochemical Science and Technology
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• v.7 no.4
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• pp.316-326
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• 2016

Development and discovery of efficient, cost-effective, and robust electrocatalysts are imperative for practical and widespread implementation of water electrolysis and fuel cell techniques in the anticipated hydrogen economy. The electrochemical reactions involved in water electrolysis, i.e., hydrogen and oxygen evolution reactions, are complex inner-sphere reactions with slow multi-electron transfer kinetics. To develop active electrocatalysts for water electrolysis, the physicochemical properties of the electrode surfaces in electrolyte solutions should be investigated and understood in detail. When electrocatalysis is conducted using nanoparticles with large surface areas and active surface states, analytical techniques with sub-nanometer resolution are required, along with material development. Scanning electrochemical microscopy (SECM) is an electrochemical technique for studying the surface reactions and properties of various types of electrodes using a very small tip electrode. Recently, the morphological and chemical characteristics of single nanoparticles and bio-enzymes for catalytic reactions were studied with nanometer resolution by combining SECM with atomic force microscopy (AFM). Herein, SECM techniques are briefly reviewed, including the AFM-SECM technique, to facilitate further development and discovery of highly active, cost-effective, and robust electrode materials for efficient electrolysis and photolysis.

• Journal of the Korean Ceramic Society
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• v.54 no.5
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• pp.406-412
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• 2017

$70V_2O_5-10Fe_2O_3-13P_2O_5-7B_2O_3$ glasses were prepared to study the electrical conductivity and catalytic properties of the structural change with crystallization. The structural changes were analyzed by determining the molecular volume from the sample density; using X-Ray Diffraction (XRD) analysis, which indicated that $V_2O_5$, $VO_2$ and $B_2O_3$ crystals in heat-treated more than 1h samples. Especially a new crystalline phase of non-stoichiometric $Fe_{0.12}V_2O_5$ was formed after 6 h heat treatment. The V-O bonding change after crystallization was analyzed by Fourier Transform Infrared Spectroscopy (FTIR); V ion change from $V^{5+}$ to $V^{4+}$ was shown by XPS. Conductivity and catalytic properties were examined based on the polaronic hopping of V and Fe ions, which exhibited different valence states with crystallization.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.669-685
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• 2015

A three-dimensional elastoplastic constitutive model, also known as a UH model (Yao et al. 2009), was developed to describe the stress-strain relationship for normally consolidated and over-consolidated soils. In this paper, an acoustic tensor and discriminator of bifurcation for the UH model are derived for the strain localization of saturated clays under undrained and fully and partially drained conditions. Analytical analysis is performed to illustrate the points of bifurcation for the UH model with different three-dimensional stress paths. Numerical analyses of cubic specimens for the bifurcation of saturated clays under undrained and fully and partially drained conditions are conducted using ABAQUS with the UH model. Analytical and numerical analyses show the similar bifurcation behaviour of overconsolidated clays in three-dimensional stress states and various drainage conditions. The results of analytical and numerical analyses show that (1) the occurrence of bifurcation is dependent on the stress path and drainage condition; and (2) bifurcation can appear in either a strain-hardening or strain-softening regime.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.513-522
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• 2019

It is not easy to refuel quickly and safely with 70 MPa hydrogen. This is because the temperature in the vehicle tank rises sharply due to Joule-Thomson effect, etc. Thus protocols such as SAE J2601 in the United States and JPEC-S 0003 in Japan were established. However, they have the problem of over-complexity and lack of versatility by setting the preconditions for hot and cold cases and introducing a number of look-up tables. This study was conducted with the ultimate goal of developing new protocols based on complete real-time communication. Thermodynamic models were made and programs were developed for hydrogen refueling simulations. Simulation results confirmed that there are five parameters in the influencing factors of the hydrogen refueling protocol.

• Journal of Environmental Science International
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• v.16 no.3
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• pp.247-253
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• 2007

Polycyclic aromatic hydrocarbons (PAHs) are a major concern because of their potential mutagenic and carcinogenic risks to human beings. One of these harmful, yet commonly observed PAHs is pyrene. Pyrene is one of the 16 PAHs listed by the United States Environmental Protection Agency as priority pollutants. The purposes of this research are to develop a method of pretreatment for PAH contaminants prior to a typical biological treatment and to demonstrate the biodegradablity of these compounds. Since pyrene is non-polar, hexane was chosen as a solvent to effectively dissolve pyrene. Pyrene solutions were treated with ozone, as it has hish oxidation capacity and electrophilic character. The intermediates and byproducts of pyrene were dissolved in alkaline water at pH 11.4 and neutralized to test for $BOD_5$, COD, and toxicity. These solutions were further ozonated and assessed of biodegradability. The first-order rate constant to was found to be between $0.121day^{-1}$ and $0.081 day^{-1}$, depending on the duration of reozonation. The $BOD_5/COD$ ratio was found to 0.66. The toxicity test showed that after 10 min of reozonation time, the byproducts and intermediates of pyrene were within the lion-toxic range of ${\pm}10%$ inhibition for E-Coli bacteria.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.563-569
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• 1996

Degradation of $Zn_3N_2$ films is studied by using several analytical techniques. Polycrystalline $Zn_3N_2$ films prepared by reactie rf magnetron sputtering are kept in the air. Electrical and optical properties are measured by using van der Pauw technique and double-beam spectrometry. Structure and chemical bonding states are studied by X-ray diffraction(XRD), Fourier transfer infrared ray spectroscopy(FT-IR) and X-ray photoelectron specroscopy (XPS). Significant differences are observed in optical properties between the degraded film and the ZnO film. XRD analysis reveals that the degraded film contains very small ZnO grains because very weak and broad ZnO peaks are observed. XPS and FT-IR measurements reveal the formation of $Zn(OH)_2$ in the degraded film. The existence of N-H bonds in degraded films is exhibited from the N 1s spectra. $Zn_3N_2$ change into the mixture of ZnO, $Zn(OH)_2$ and an ammonium salt.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.518-520
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• 1997

Recently, thiophene oligomer with short chain lengths has received much attention as model compounds for facilitating better understanding of electronic and optical properties of polymers, because oligomer is well-defined chemical systems and its conjugation chain length can be exactly controlled. Moreover, organic this films based on conjugated thiophene oligomer have potential for application to electronic and optoelectronic devices such as MISFETs(metal-insulator-semiconductor field-effect transistors) and LEDs(light-emitting diodes). However, there is little knowledge on electronic and structural properties of linear-conjugated oligothiophenes in solid states, compared with those in solutions. $\alpha$-sexithienyl($\alpha$-6T) thin-films were deposited by OMBD(Organic Molecular Beam Deposition) technique, where the $\alpha$-6T was synthesized and purified by the sublimation method. The $\alpha$-6T films were deposited under various conditions. The effects of deposition rate, substrate temperature, and vacuum pressure on the formation of these films have been studied. The molecules in the $\alpha$-6T film deposited at a low deposition rate under a high vacuum were aligned almost perpendicular to the substrate. The $\alpha$-6T films deposited at an elevated substrate temperature showed higher conductivity than the film deposited at room temperature. Electrical characterization of these films will be also executed by using four-point probe measurement technique.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.99-102
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• 2003

Tin dioxide thin films were deposited at $375^{\circ}C$ on alumina substrate by metal-organic chemical vapor deposition process to find the relationship between physicochemical properties and the annealing treatments. The small grains with heat treatments grew to the bunch of grains and then showed the hillocks on the film surface. The thickness decreased with annealing treatment. The measured binding energy (BE) and branching ratio of the Sn 3d spin-orbital doublet were typical of oxidized states of Sn and the BE of the O1s core level of about 530~530.65eV also confirmed the presence of O-Sn bonds. The BE of oxygen and tin with annealing treatment shifted to higher position. O/Sn atomic ratios of films deposited at $375^{\circ}C$ for 2min and 4min were 1.99 and 2.01, respectively. The value of the atomic ratio O/Sn of films deposited at $375^{\circ}C$ for 2min changed from 1.99 to 2.45 with annealing treatment. Gas sensitivity depended on annealing temperature, the sensitivity increased with increasing annealing temperature.

• Journal of Pharmaceutical Investigation
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• v.23 no.4
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• pp.231-254
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• 1993

These days, it is not uncommon that a same kind of drug is circulated globally. However, the qualities of excipients used in the same drug have to be sometimes different depending on the different requirements in the qualities stipulated by each country. For a supplier of pharmaceutical excipients, it is generally necessary to carry out different tests on the same kind of testing criteria depending on the country of destination. Thus, the discrepancies between compendium requirements of pharmaceutical excipients create severe problems in various area of industrial activities. The decision of the United States Pharmacopoeia, European Pharmacopoeia and Japanese Pharmacopoeia Commissions to harmonize the requirements is a unique chance for the industries to overcome these problems. On the other hand, discrepancies of general test methods and requirements in each monograph of pharmaceutical excipient between the compendia valid at present are in most cases extensive. Consequently their harmonization needs a lot of detailed work requiring strong support from the industry. Based on these circumstances, pharmaceutical excipients councils have been established first in U.S.A. and successively in Europe and in Japan to contribute to the harmorization process. We should like to review here the progress since the Orlando Conference in 1991 and comment about the matters at issue with regard to the international harmonization of pharmaceutical excipients.