• Proceedings of the Korean Vacuum Society Conference
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• 2009.02a
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• pp.280.1-280.1
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• 2009

• Proceedings of the Korean Vacuum Society Conference
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• 2009.02a
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• pp.250.2-250.2
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• 2009

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.172-172
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• 1999

Perovskite Manganese Oxide has been intensively investigated since the discovery of the colossal magnetoresistive(CMR) effect. In this paper, we studied the effect of temperature dependence and various doping dependence of rare earth site ions of La0.7-xPrxCa0.3MnO3 series using Ultraviolet Photoelectron spectroscopy(UPS). They show unusual temperature dependent features and the doped rare earth ions seem to affect the electron-phonon coupling strongly. We found clear evidence of metal-insulator transition from the spectral density at the Fermi level. but the transition temperature is lower than that deduced from transport measurements. Also we found that the spectral features change as time goes on implying that the surface of these materials is somewhat unstable in the vacuum. We can conclude from these results that the surface oxygen atoms correlated to the hopping electrons can escape from the material into the vacuum and that the surface state of these material is different from the bulk state.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.421-422
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• 2011

The first part is about development of a liquid target for a neutron source, which is designed to overcome many of the limitations of traditional beam-target neutron generators by utilizing a liquid target neutron source. One of the most critical aspects of the beam-target neutron generator is the target integrity under the beam exposure. A liquid target can be a good solution to overcome damage to the target such as target erosion and depletion of hydrogen isotopes in the active layer, especially for the one operating at high neutron fluxes with no need for water cooling. There is no inherent target lifetime for the liquid target neutron generator when used with continuous refreshment of the target surface exposed to the energetic beam. In this work, liquid target containing hydrogen has been developed and tested in vacuum environment. Potentially, liquid targets could allow a point neutron source whose spatial extension is on the order of 1 to $10{\mu}m$. And the second is about the vacuum ultraviolet (VUV) spectrometer which is designed as a five-channel spectral system for ITER main plasma measurement. To develop and verify the design, a two-channel prototype system was fabricated with No. 3 (14.4 nm~31.8 nm) and No. 4 (29.0 nm~60.0 nm) among the five channels. For test of the prototype system, a hollow cathode lamp is used as a light source. The system is composed of a collimating mirror to collect the light from source to slit, and two holographic diffraction gratings with toroidal geometry to diffract and also to collimate the light from the common slit to detectors. The two gratings are positioned at different optical distances and heights as designed. To study the appropriate detector for ITER VUV system, two different electronic detectors of the back-illuminated charge coupled device and the micro-channel plate electron multiplier were installed and the performance has been investigated and compared in the same experimental conditions. The overall system performance was verified by measuring the spectrums.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.290.1-290.1
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• 2016

Grapehen, a single atomic layer of graphite, has been in the spotlight and researched in vaious fields, because its fine mechanical, electrical properties, flexibility and transparence. Synthesis methods for large-area graphene such as chemical vaper deposition (CVD) and mechanical, chemical exfoliation have been reported. In particular, chemical exfoliation method receive attention due to low cost process. Chemical exfoliation method require reduction of graphene oxide in the process of exfoliation such as chemical reduction by strong reductant, thermal reduction on high temperature, and optical reduction via ultraviolet light exposure. Among these reduction methods, optical reduction is free from damage by strong reductant and high temperature. However, optical reduction is economically infeasible because the high cost of short-wavelength ultraviolet light sorce. In this paper, we make graphene-oxide and lanthanoid ion mixture aqueous solution which has highly optical absorbency in selective wevelength region. Sequentially, we synthesize reduced graphene oxide (RGO) using the solution and visible laser beam. Concretely, graphene oxide is made by modified hummer's method and mix with 1 ml each ultraviolet ray absorbent Gd3+ ion, Green laser absorbent Tb3+ ion, Red laser absorbent Eu3+ ion. After that, we revivify graphene oxide by laser exposure of 300 ~ 800 nm layser 1mW/cm2 +. We demonstrate reproducibility and repeatability of RGO through FT-IR, UV-VIS, Low temperature PL, SEM, XPS and electrical measurement.

• Proceedings of the Korean Vacuum Society Conference
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• 2005.02a
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• pp.85-85
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• 2005

• Proceedings of the Korean Vacuum Society Conference
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• 2003.02a
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• pp.224-224
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• 2003

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.198.2-198.2
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• 2016

Reactive oxygen and nitrogen species (RONS) can be generated by using non-thermal atmospheric pressure plasma jet which have profound biomedical applications [1, 2]. In this work, reactive oxygen species like hydroxyl radical (OH) are generated by using non-thermal direct plasma jet above water surface using Ar gas and their properties have been studied using ultraviolet absorption spectroscopy. OH radicals are found to be generated simultaneously with the discharge current with concentration of $2.7{\times}1015/cm3$ at 7mm above water surface while their persistence time have been measured to be $2.8{\mu}S$. In addition, it has been shown that plasma initiated ultraviolets play a major role to generate RONS inside water. Further works are going on to measure the temporal behavior of OH and $O2^*-$.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.177-180
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• 1997

Low Energy Electron Diffraction (LEED) apparatus was made to confirm the surface structure and to determine the direction of the structure for the Angle Resolved Ultraviolet Photoemission Spectroscopy(ARUPS) study. To determine the parameters needed for the design of the apparatus, computer simulation was used. Our LEED has 3 grids. The distance between sample and sccreen is 75 mm, and the viewing angle is $80^{\circ}$. The LEED apparatus was tested by investigating the Si(001) and $Al_2O_3$(0001) surface.

• Journal of the Korean Vacuum Society
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• v.8 no.1
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• pp.9-12
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• 1999

An electron energy analyzer for Angle Resolved Ultraviolet Photoelectron Spectroscopy (ARUPS) has been constructed and tested. This analyzer consists of tandem 3 element electron lenses and two concentric hemispherical capacitors. Electronic structure of clean Cu(100) surface has been studied to test the feature of the analyzer. The ultimate energy resolution is 40 me V and angle resolution is $0.2^{\circ}$.