• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.4
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• pp.497-508
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• 2020

In the geochemical field, the chemical speciation of hexavalent uranium (U(VI)) has been widely investigated by performing measurements to determine its luminescence properties, namely the excitation, emission, and lifetime. Of these properties, the excitation has been relatively overlooked in most time-resolved laser fluorescence spectroscopy (TRLFS) studies. In this study, TRLFS and continuous-wave excitation-emission matrix spectroscopy are adopted to characterize the excitation properties of U(VI) surface species that interact with amorphous silica. The luminescence spectra of U(VI) measured from a silica suspension and silica sediment showed very similar spectral shapes with similar lifetime values. In contrast, the excitation spectra of U(VI) measured from these samples were significantly different. The results show that distinctive excitation maxima appeared at approximately 220 and 280 nm for the silica suspension and silica sediment, respectively.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.1
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• pp.54-58
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• 1999

We deposited diamond-like carbon (DLC) films using ion beam sputtering of a graphite target on flat substrates for use as a thin film field emitter. An n-type silicon wafer, titanium-coated silicon, and indium tin oxide (ITO) coated glass were used as a substrate. All films exhibited a sudden increase in the emission after a breakdown occurred at high voltage. The morphology of the films after the breakdown depended on the substrate. On ITO and Ti substrates, the DLC film peeled off upon breakdown, but on the Si substrate the surface melting due to breakdown resulted in the formation of various structures such as a sharp point, mound, and crater. By scanning the deformed surface with a tip anode, we found that the emission was concentrated at the deformed sites, indicating that the field enhancement due to the morphology change was responsible for the increased emission.

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.37-43
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• 2006

Carbon nanotube cathodes (CNT cathodes) were fabricated by a screen printing method using multi-walled carbon nanotubes. The effects of surface treatment on CNT cathodes were investigated for use in high efficiency field emission displays. The optimum surface treatment for a CNT cathode is dependent on a relative bonding force of CNT films on the cathode after a heat treatment. Because of the high bonding force used in the Liquid method, this method is recommended for CNT cathodes which are heat-treated at $390^{\circ}C$ in a $N_2$ atmosphere. The Rolling method is applicable for CNT cathodes fabricated at $350^{\circ}C$ in an atmosphere of air. The results of this study provide basic criteria for the selection of an appropriate surface treatment for large area CNT cathodes.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.349-350
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• 2012

Porous silicon (PS) was prepared by electrochemical anodization. Ultra-thin zinc oxide (ZnO) capping layers were deposited on the PS by plasma-assisted molecular beam epitaxy (PA-MBE). The effects of the ZnO capping layers on the properties of the as-prepared PS were investigated using scanning electron microscopy (SEM) and photoluminescence (PL). The as-prepared PS has circular pores over the entire surface. Its structure is similar to a sponge where the quantum confinement effect (QCE) plays a fundamental role. It was found that the dominant red emission of the porous silicon was tuned to white light emission by simple deposition of the ultra-thin ZnO capping layers. Specifically, the intensity of white light emission was observed to be enhanced by increasing the growth time from 1 to 3 min.

• Bulletin of the Korean Chemical Society
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• v.21 no.8
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• pp.769-773
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• 2000

The dependence of photoluminescence (PL) and photoluminescence itation (PLE) on preparation condi-tions and the aging of porous silicon carbide (PSC) have been investigatted. The fiber size of the material pre-pared under dark-current mode, labele d DCM, was larger than that of the photoassisted (PA)process.The intensity of the PL spectrum for the PA condition was higher than that of the DCM condition. The PA condition giving small fiber size exhibited amore prominent high-energy component but the emission bands of both con-ditionsobserved were rather similar. The origin of the PL may have played an importantrole in the surface defect center introduced by the reaction conditions ofHFatthe surface of the silicon carbide. Selective excita-tion of the PL bandsusingdifferent excitation wavelengths has been used to identify distinct componentswith-in the PL bandwidth. Two main PL bands with peak wavelength of494 and534 nm were clearly resolved. On the other hand, selectivc emission of the PLEbands using different emission wavelengths has been used to identify distinct components within the PLE bandwidth. The higher energy band with peak wavelength of 338 nm and the lower energy bands involving 390,451 and 500 nm were clearly resolved. According to the pro-ionged aging in air, PL spectra appearedasone band, This emission probably originated from states localized to the band-to-band recombination due to the oxidation on the crystallite surface.

• Journal of the Korean Society of Safety
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• v.30 no.1
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• pp.111-118
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• 2015

In this study, we carried out the emissions analysis of CO and $non-CO_2$ for the age-classes of various pine trees(Pinus koraiensis, Pinus densiflora, Pinus rigida Mill., Pinus thunbergii Parl.) to estimate of emission factors of the crown layer and surface layer in the forest fire. We used the thermal characteristic analyzer cone heater and NDIR analyzer in order to measure amount of emission. As a result, the major emissions of Pinus koraiensis were $CO_2$ and $CH_4$ and that of Pinus thunbergii Parl. was only CO. The major emissions of the most of pine trees were NO and $N_2O$. The $CO_2$ emission of Pinus thunbergii Parl. was the highest about as $7.26{\times}10^{-2}{\sim}1.63{\times}10^{-1}g$ and next came Pinus densiflora, Pinus koraiensis, Pinus rigida Mill.. And the CO emission of Pinus thunbergii Parl. was about $5.14{\times}10^{-3}{\sim}6.58{\times}10^{-3}g$ and followed by Pinus densiflora, Pinus koraiensis, Pinus rigida Mill.. The emissions of $CH_4$, NO, and $N_2O$ showed small differences between species and the emission of $CH_4$ was $8.37{\times}10^{-5}{\sim}2.55{\times}10^{-4}g$, and NO was $6.65{\times}10^{-5}{\sim}2.0{\times}10^{-4}g$ and $N_2O$ was $1.42{\times}10^{-4}{\sim}2.09{\times}10^{-3}g$ in all species. Particularly, the emission of Pinus thunbergii Parl. was the highest in all pine trees except $CH_4$.

• Analytical Science and Technology
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• v.20 no.5
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• pp.413-418
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• 2007

Poly(vinylpyrrolidone) stabilized cadmium sulfide (CdS) nanoparticles were loaded onto the surface of silica ($SiO_2$) nanoparticles by using ${\gamma}$-irradiation. TEM micrograph reveals the presence of ~20nm sized CdS nanoparticles on the surface of $SiO_2$ nanoparticles. XRD patterns confirm the crystalline. PL spectra of the simple PVP-stabilized CdS nanoparticle and $SiO_2$@CdS composite confirm the differences in the emission characteristics between them. Two prominent emission peaks were noted around 550 nm and 600 nm for PVP-stabilized CdS nanoparticles). The emission peaks noted for the PVP-stabilized CdS nanoparticles were found to be blue shifted for $SiO_2$@CdS composites. Besides, an additional emission peak around 450 nm was noticed for the $SiO_2$@CdS composite. The presence of CdS nanoparticles influence the emission characteristics and induce quantum confinement effect.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.696-699
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• 2004

Of the emissive display technologies, field emission displays using pasted carbon nanotubes offer several advantages over other competing cathode materials such as low driving voltage, possible large-area and low-cost processes. In this study, formulation of carbon nanotube paste and its electron field emission properties are characterized. Also the effects of additive powders and surface morphology on electron emission are reported.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1867-1869
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• 1999

Pulse electric field induced electron emission from ferroelectrics has been studied with Pb$(Zr_xTi_{1-x})O_3$ ceramics with varying Zr/Ti ratio from 35/65 to 65/35, Electron emission was proved to be concentrated on the electrode edge by emission profile test and emission capture photographs. The 65/35 composition showed largest emission charge in lowest field and lowest emission threshold field. The emission characteristics are closely dependent on their ferroelectric properties in hysteresis curve. Electron emission charge increases with the polarization charge and emission threshold voltage is dependent on coercive field regardless of their composition. But dielectric constant has little relation with emission property. Electron emission charge increases exponentially with pulse electric field irrespective of composition. On the assumption that the surface potential is linear with the pulse electric field, electron emission can be regarded as a field emission at the electrode edge using Fowler-Nordheim plot of ln$(Q_e/E_{fe})$ to $1/E_{fe}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.51-51
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• 2008

Carbon nanotubes (CNTs) have long been reported as an ideal material due to their excellent electrical conductivity and chemical and mechanical stability as well as their high aspect ratios for field emission devices. CNT emitters made by screen printing the organic binder-based CNT paste may act as a source to release gases inside a vacuum panel. These residual gases may cause a catastrophic damage by electrical arcing or ion bombardment to the vacuum microelectronic devices and may change their physical or electrical properties by adsorbing on the CNT emitter surface. In this study, we analyzed the composition of residual gases inside the vacuum-sealed panel by residual gas analyzer (RGA), investigating the effects of individual gases of different kinds at several pressures on the field emission characteristics of CNT emitters. The residual gases included $H_2$, CO, $CO_2$, $N_2$, $CH_4$, $H_2O$, $C_2H_6$, and Ar. Effect of residual gases on the field emission was studied by observing the variation of the pulse voltages with the duty ratio of3.3% to keep the constant emission current of $28{\mu}A$. Each gas species was introduced to a vacuum chamber up to three different pressures ($5\times10^{-7}$, $5\times10^{-6}$, and $5\times10^{-5}$ torr) each for 1 h while electron emission was continued. The three different pressure regions were separated by keeping a high vacuum of $\sim10^{-8}$ torr for a 1 h. The emission was terminated 6 h after the third gas exposure was completed. Field emission characteristics under residual gases will be discussed in terms of their adsorption and desorption on the surface of CNTs and the resultant change of work function.