• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.33-37
• /
• 2002

The phosphorescence powder, $SrA1_2O_4:Eu^{2+}$, synthesized by a Polymerized Complex Method(PCM), has been compared with that by a Solid-State Reaction(SSR), and their luminescence characteristics have been studied. The PCM powders were synthesized at $900^{\circ}C$ and the SSR powders at $1200^{\circ}C$. The size of PCM powders was about $0.1{\mu}m$ and one tenth of that of the SSR powders, which was due to the lower synthesized temperature. On the other hand, residual carbon in the PCM powders decreased with an increase in the crystallinity of host lattice, which was responsible for the non-white color of the powders. Both powders showed the maximum luminescence peaks around 520nm in the wave length at room temperature. However, the peak position for the PCM powders was shifted to a slightly lower wavelength and the value of half-width of the peak was broad comparing to that of the SSR powders, and the peak intensity decreased significantly. Such a change in the luminescence characteristics was due to the large difference in size for two types of powders and partly the residual carbon in the PCM powders.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.4
• /
• pp.207-212
• /
• 2012

A single phase $Mg_3Sb_2$ alloy was synthesized by melting the mixture of Mg and Sb metal powders at 1173 K. The figure of merit of the $Mg_3Sb_2$ prepared by melting method increased with temperature and showed a value of $2.39{\times}10^{-2}$ at 593 K. When the $Mg_3Sb_2$ powders were milled at high speed in a planetary ball mill for 12~48 h, Zintle phase ($Mg_3Sb_2$) was maintained as a main phase, but its crystallinity became deteriorated and elemental Sb phase appeared. Sb phase free $Mg_3Sb_2$ could be obtained by the mechanical alloying of high speed ball milling for 24 h using elemental Mg and Sb powder mixtures.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.5
• /
• pp.217-221
• /
• 2003

In this work, chemical-solution derived silicate fibers were prepared by mixing tetraethyl orthosilicate, ethanol, distilled water, and hydrochloric acid in order to investigate surface roughness of fiber. Silicate fibers were drawn by using a viscous solution after evaporation at $80^{\circ}C$. The dried gel fibers were finally annealed at $1000^{\circ}C$, $1100^{\circ}C$, $1200^{\circ}C$ and $^1300{\circ}C$ for 60 min in dried air (flow rate = ∼200 ml/min). The crystallinity of the heat-treated silica fiber was analyzed by the X-ray diffraction $\theta$-2$\theta$ scan. A field emission-scanning electron microscope and an atomic force microscope were used to evaluate surface properties. The silicate fiber annealed at $1300^{\circ}C$ showed high value of root mean square roughness and had a relatively inhomogeneous surface structure.

• Journal of the Korea Convergence Society
• /
• v.11 no.10
• /
• pp.1-7
• /
• 2020

The manufacturing process of the resistive variable memory device, which is the based of neuromorphic device, maintained the continuity of vacuum process and applied plasma module suitable for the production of the ReRAM(resistive random access memory) and process technology for the neuromorphic computing, which ensures high integrated and high reliability. The ReRAM device of the oxide thin-film applied to the plasma module was fabricated, and research to improve the properties of the device was conducted through various experiments through changes in materials and process methods. ReRAM device based on TiO₂/TiOx of oxide thin-film using plasma module was completed. Crystallinity measured by XRD rutile, HRS:LRS current value is 2.99 × 10³ ratio or higher, driving voltage was measured using a semiconductor parameter, and it was confirmed that it can be driven at low voltage of 0.3 V or less. It was possible to fabricate a neuromorphic ReRAM device using oxygen gas in a previously developed plasma module, and TiOx thin-films were deposited to confirm performance.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.315-315
• /
• 2013

We report the electronic structure modification in the swift heavy ion (SHI) irradiated N-doped ZnO thin films prepared by RF sputtering from ZnO target in different ratio of Ar/$N_2$ gas mixture using highly pure $N_2$ gas. The different N-ZnO thin lms were then irradiated with 120 MeV Ag ion beam with different doses ranging from $1{\times}10^{11}$ to $5{\times}10^{12}$ ions/$cm^2$ and characterized by XRD and near edge X-ray absorption ne structure (NEXAFS) at N and O K-edges. The NEXAFS measurements provide direct evidence of O 2p and Zn 3d orbital hybridization and also the bonding of N ions with Zn and O ions. The minimum value of resistivity of $790{\Omega}cm$, a Hall mobility of $22cm^2V^-1s^-1$ and the carrier concentration of $3.6{\times}10^{14}cm^{-3}$ were yielded at 75% $N_2$. X-ray diffraction (XRD) measurements revealed that N-doped ZnO films had the preferential orientation of (002) plane for all samples, while crystallinity start decreasing at 32.5% $N_2$. The average crystallite size varies from 5.7 to 8.2 nm for 75% and then decreases to 7.8 nm for 80% $Ar:N_2$ ratio.

• Current Photovoltaic Research
• /
• v.3 no.2
• /
• pp.39-44
• /
• 2015

$Cu(In,Ga)_3Se_5$ (${\beta}-CIGS$) has a band gap of 1.35 eV which is an optimum value for high solar-energy conversion efficiency. However, ${\beta}-CIGS$ film was not well characterized yet due to lower efficiency compared to $Cu(In,Ga)Se_2$ (${\alpha}-CIGS$). In this work, ${\beta}-CIGS$ films were fabricated by a three-stage co-evaporation of elemental sources with various Se fluxes. As the Se flux increased, the crystallinity of ${\beta}-CIGS$ phase was improved from the analysis of Raman spectroscopy and a deep-level defect was reduced from the analysis of photoluminescence spectroscopy. A Se treatment of the ${\beta}-CIGS$ film at $200^{\circ}C$ increased Ga content and decreased Cu content at the surface of the film. With the Se treatment at $200^{\circ}C$, the cell efficiency was greatly improved for the CIGS films prepared with low Se flux due to the increase of short-circuit current and fill factor. It was found that the main reason of performance improvement was lower Cu content at the surface instead of higher Ga content.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1995.02a
• /
• pp.36-36
• /
• 1995

The cubic (zinc blende) CdSe eppilayers were grown on GaAs(100) substrates by electron beam (e-beam) evapporation technique. X-ray scans with copper $K\alpha$ radiation indicate that the CdSe eppilayers are zinc blende. The lattice pparameter obtained from the (400) reflection is 6.077$\AA$, which is in excellent agreement with the value repported in the literature for zinc blende CdSe. The orientation of as-grown CdSe eppilayer is determined by electron channeling ppatterns(ECpp). The crystallinity of heteroeppitaxial CdSe layers were investigated based on the double crystal x-ray rocking curve(DCRC). The deppendence of the rocking curve width on layer thickness was studied. The FWHM(full width at half maximum) of CdSe eppilayers grown on GaAs(100) substrates is decreasing with increasing eppilayer thickness. The carrier concentration and mobility of the as-grown eppilayers deduced Hall data by van der ppauw method, are about 7$\times$1017 cm-3 and 2$\times$102 $\textrm{cm}^2$ / sec at room tempperature, resppectively. The energy gapp was determinded from the pphotocurrent sppectrum. In pphotocurrent sppectrum of a 1-${\mu}{\textrm}{m}$-thick CdSe eppilayer at 30K, the ppeak at 1.746 eV is due to the free exciton of cubic CdSe. In summary, We have shown that eppilayers of zinc blende CdSe can be grown on GaAs(100) substrates by e-beam, desppite the large mismatch between eppilayer and substrate, as well as the natural ppreference for CdSe to form in the wurtzite structure.

• Korean Chemical Engineering Research
• /
• v.47 no.4
• /
• pp.476-480
• /
• 2009

A polymer composite electrolyte of a blend of poly(methyl methacrylate)(PMMA) and poly(ethylene oxide) (PEO) as a host polymer, the ethylene carbonate as a solvent, and $LiClO_4$ as a salt was studied. The crystallinity of the polymer electrolytes was evaluated using differential scanning calorimeter(DSC). The ionic conductivity of the polymer electrolytes was measured by frequency response analyzer(FRA) method. The effect of PEO/PMMA blend ratios on the ionic conduction in these electrolytes was investigated. The electrolyte films showed a phase separation due to immiscibility of the PMMA with the PEO. The PMMA-rich phase and the PEO-rich phase were produced during a film casting. The ionic conductivity of blend electrolyte was dependent on the content of PMMA and showed the highest value at 20 wt.%. However, when PMMA content exceeds 20 wt.%, the ionic conductivity was decreased due to the slow ionic transport through the PMMA-rich phase.

• Journal of the Microelectronics and Packaging Society
• /
• v.16 no.4
• /
• pp.17-22
• /
• 2009

Two different organic-inorganic hybrid thin film transistors (OITFTs) with the structures of glass/ITO/ZnO/PMMA/Al (staggered structure) and glass/ITO/PMMA/ZnO/Al (inverted staggered structure), were fabricated and their electrical and structural properties were compared. The ZnO thin films used as active channel layers were deposited by the atomic layer deposition (ALD) method at a temperature of $100^{\circ}C$. To investigate the effect of the substrates on their properties, the ZnO films were deposited on bare glass, PMMA/glass and ITO/glass substrates and their crystal properties and surface morphologies were analyzed. The structural properties of the ZnO films varied with the substrate conditions. The ZnO film deposited on the ITO/glass substrate showed better crystallinity and morphologies, such as a higher preferred c-axis orientation, lower FWHM value and larger particle size compared with the one deposited on the PMMA/glass substrate. The field effect mobility ($\mu$), threshold voltage ($V_T$) and $I_{on/off}$ switching ratio for the OITFT with the staggered structure were about $0.61\;cm^2/V{\cdot}s$, 5.5 V and $10^2$, whereas those of the OITFT with the inverted staggered structure were found to be $0.31\;cm^2/V{\cdot}s$, 6.8 V and 10, respectively. The improved electrical properties for the staggered OITFTs may originate from the improved crystal properties and larger particle size of the ZnO active layer.

• Applied Chemistry for Engineering
• /
• v.26 no.6
• /
• pp.659-665
• /
• 2015

Loading of hydrophobic ${\alpha}$-tocopherol into nanostructured lipid carrier (NLC) was performed for improving its oxidative stability. First, various NLCs with different constituents and mixing ratios were prepared and their characteristics were investigated. While the stable NLCs were made when cetyl palmitate (CP) or glyceryl monosterate (GMS) was used as a solid lipid, the phase separation occurred in the NLCs consisting of stearic acid. Particle sizes of the NLCs were several hundreds of nanometers and the size decreased with increasing the ratio of solvent to lipid. It was examined from DSC thermogram and anisotropy test that the degree of crystallinity of the lipid phase decreased and the lipid matrix became less ordered when octyldodecanol, a long chain fatty alcohol, was added into the solid lipid. The oxidative stability of ${\alpha}$-tocopherol in NLC was remarkably improved compared to that in solution or emulsion under high temperature ($45^{\circ}C$) and UV radiation, which was verified through DPPH test and peroxide value measurement.