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ABSTRACT: AC inorganic electroluminescence (EL) devices were fabricated using the emitting layer composed of phosphor-single-walled carbon nanotubes (SWCNTs) composite (PSC) to utilize the local field enhancement of SWCNTs. In order to enhance the electric field in an emitting layer with minimized current paths, bare long SWCNTs were shortened by cryogenic crushing method. After electrical aging treatment of the PSC device, partly formed short SWCNT networks in the emitting layer were effectively removed during the electrical aging treatment. High performance of 60% and 43% increase in efficiency and luminance, respectively, was achieved. This PSC device with short SWCNTs could lead to high brightness due to increased electron tunneling into phosphor. The PSC device reveals the importance of high electric field by SWCNTs leading to high EL performance.
IEEE Electron Device Letters 12/2010; · 2.85 Impact Factor
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ABSTRACT: Alternating-current-type inorganic powder electroluminescence (PEL) devices were successfully fabricated on four kinds of paper substrates, i.e., glossy paper, sticker paper, magazine paper, and newspaper. To protect the paper from wet chemical and heating processes during the formation of the PEL device, the paper substrate was coated with a spin-on-glass layer that served as a buffer layer. In spite of the fragility of paper, quite satisfactory results were obtained-the performance of paper-based PEL devices was almost equivalent to that of PEL devices on a plastic substrate. Extension of a substrate to paper, even to flimsy daily newspaper, will widen the opportunity of PEL devices as one of flexible and disposable displays.
IEEE Transactions on Electron Devices 07/2010; · 2.32 Impact Factor
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ABSTRACT: Carbon nanotubes in printed field emission arrays are known to be often damaged during field emission. A high-resolution transmission electron microscopy and Raman scattering spectra suggest that the degraded structure is mainly determined by electrical treatment conditions. A nonstationary alternating-current treatment has caused emitters to be thicker and fewer with loss of crystallinity but improved the emission brightness and uniformity, while a direct-current treatment has shown little influence. The experimental observations can be quantitatively explained by the analytical estimation on the apex radius as well as the work function using the Seppen–Katamuki chart from the Fowler–Nordheim characteristics.
Applied Physics Letters 01/2010; 96(2):023105-023105-3. · 3.84 Impact Factor
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Chan-Wook Baik, Jeonghee Lee,
Deuk Seok Chung,
Jun Hee Choi,
In-Taek Han,
Ha Jin Kim,
Shang Hyeun Park,
Sun Il Kim,
Yong Wan Jin,
Jong-Min Kim,
Jin Young Kim,
SeGi Yu,
Kyu-Ha Jang,
Gun-Sik Park
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ABSTRACT: We report a physical mechanism of controlling vacuum breakdown in field emission from carbon nanotubes (CNTs). The thermal evaporation or runaway of CNT emitters is considered to be responsible for destructive vacuum breakdowns due to an overcurrent through electronically shorted circuits, where misaligned or irregularly long CNT emitters were found. The occurrence of the destructive breakdown, however, could be under control after an electrical treatment using soft breakdowns. Significant improvements of field emission stability and uniformity were achieved by optimally controlled soft breakdowns, which eliminated the short circuits and recovered the field emission with no destruction of electrodes.
IEEE Transactions on Nanotechnology 12/2007; · 2.29 Impact Factor
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Chan-Wook Baik, Jeonghee Lee,
Deuk Seok Chung,
Seong Chan Jun,
Jun Hee Choi,
Byung Kwon Song,
Min Jong Bae,
Tae Won Jeong,
Jung Na Heo,
Yong Wan Jin,
Jong-Min Kim,
SeGi Yu,
Kyu-Ha Jang,
Gun-Sik Park
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ABSTRACT: The field-emission characteristics of carbon nanotubes (CNTs), such as uniformity and brightness, were improved by electrical treatment using nonstationary electric fields between the cathode of screen-printed CNT emitters and the anode of a phosphor-coated indium-tin-oxide glass substrate in diode configuration. Dead or weak emission spots, where almost no emission of electrons was observed, started to emit electrons by applying an alternating-current voltage to the cathode electrode and a constant voltage to the anode electrode. The nonstationary electrical treatment was more effective than the direct-current (dc) and the square-pulsed electrical treatments for the emission uniformity and brightness. It was found that the nonstationary electrical treatment not only activated CNT emitters but also suppressed abnormally high emission spots without the drawbacks of electrical breakdown. Consequently, more than 1.8 and 1.3 times improvements of emission uniformity and brightness, respectively, were obtained after the treatment, when compared with the dc electrical treatment for the same amount of emission currents and the same duration of the treatments. Therefore, the method can be effectively applied to field-emission devices based on CNTs for the enhancement of emission properties.
IEEE Transactions on Electron Devices 10/2007; · 2.32 Impact Factor
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ABSTRACT: Vertically aligned ZnO nanorods were grown on the substrate by sonication. Transmission electron microscopy, photoluminescence, and X-ray diffraction were performed for nanorods synthesized by sonication, which leads to formation of ZnO crystals. For field emission measurements, ZnO nanorods were used as cathode and a green phosphor coated ITO glass was used as anode, where cathode and anode plates were separated by a spacer of 270 mum. Therefore, due to the easy fabrication process and good field emission characteristics, these sonochemically synthesized ZnO nanorods can be regarded as one of key potential field emitters.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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Taewon Jeong,
Jungna Heo, Jeonghee Lee,
Sanghyun Park,
Yongwan Jin,
J. M. Kim,
Taesik Oh,
Chongwyun Park,
Ji-Beom Yoo,
Byoungyun Gong,
Naesung Lee,
SeGi Yu
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ABSTRACT: Multiwalled carbon nanotube (MWNT) emitters fabricated by the metal intermediation process were studied. This was intended to allow strong adhesion and high electrical contact between the cathode electrode and MWNT emitters. The process was performed by hot-pressed bonding of a metal layer to a MWNT film surface, where the metal layer was deposited on a main substrate. Through this process, MWNTs have open and sharp ends, and the metal layer and the MWNTs have strong electrical contact. Together with unchanged crystallinity of MWNTs as before the process, these effects improve the field emission properties, resulting in 64% reduction of turn on field and two to three orders of magnitude increase of current density.
Journal of Applied Physics 10/2006; · 2.17 Impact Factor
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ABSTRACT: We investigated the effect of plasma treatment on single-walled carbon nanotube (SWCNT) field emitters, which were fabricated by printing a photoimageable SWCNT paste, to improve emission lifetime. The treatment was performed by applying a dc pulsed voltage between two electrodes, where the cathode was the SWCNT emitter to be treated and the anode was a bare indium-doped tin oxide glass, under inert gas (Xe/Ne) atmosphere. With increasing applied voltage and treatment time, the stability of the emission current at a constant electric field is improved, while the field to reach a required emission current becomes high. We attribute the improved emission stability to the removal of a small portion of protruding emitters, which dominate initial emission characteristics. The elimination of small number of prominent emitters allows a greater number of emitters to be active on emission with a compensation for higher electric-field application. We expect that the plasma treatment introduced in this letter will provide a quick and easy way to improve emission lifetime, which is essential for the commercialization of field emission display.
Applied Physics Letters 10/2005; 87(16):163112-163112-3. · 3.84 Impact Factor
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ABSTRACT: Field emission characteristics were investigated for zinc oxide nanostructures which were grown on NiO catalyzed silicon (100) substrate by chemical vapor deposition method. The asgrown zinc oxide showed needle-shaped nanostructures with tip diameters of 20∼40 nm and length of 3∼5 νm. The turn-on field was found to be about 6 V/νm at a current density of 1 νA/cm2. After several field emission measurements, the turn-on field was increased up to 8.5 V/νm and the magnitude of field enhancement factor was decreased from 1190 to 940. According to SEM, the tip diameter increase of the zinc oxide to 60 nm was observed after several emission measurements. Therefore, degradation of the field emission characteristic after measurements is attributed to this deformation of the tip shape.
MRS Proceedings. 12/2002; 776.
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SeGi Yu,
Whikun Yi, Jeonghee Lee,
Taewon Jeong,
Sunghwan Jin,
Jungna Heo,
J. H. Kang,
Y. S. Choi,
Chang Soo Lee,
Ji-Beom Yoo,
J. M. Kim
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ABSTRACT: Field emission energy distribution (FEED) has been measured for undergate-type triode carbon nanotube (CNT) field emitters where the gate electrodes are located underneath the cathode electrodes. The diode-type emission for these CNT emitters was found to follow the Fowler–Nordheim relation, whereas the triode-type emission exhibited the deviation from this relation. The FEED peaks for the undergate CNT emitters under the triode-type emission shifted to lower energy as the gate voltage increased, indicating nonmetallic behavior for the CNT emitters. There exist two different characteristic FEED peaks, where their peak energy shifts as a function of the gate voltage belong to two different slopes. From the difference in the position and intensity of the peaks, it was found that one was field emission directly from CNTs and the other might be emitted from CNTs through glass powders which were added during the CNT field emitter fabrication process. © 2002 American Institute of Physics.
Applied Physics Letters 05/2002; 80(21):4036-4038. · 3.84 Impact Factor
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Segi Yu,
Whikun Yi,
Taewon Jeong,
Seok Won,
Kim, Jeonghee Lee,
Jungna Heo,
Soo Chang,
Lee,
Ji-Beom Yoo,
Young Hee Lee,
J M Kim
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ABSTRACT: Due to a recent discovery of large secondary electron emission from MgO-coated multiwalled carbon nanotubes (MgO/MWCNTs) (J. Appl. Phys. 89 (2001) 4091), much interest has been focused on this topic for its potential application as an electron emission source. Field emission and field emission energy distribution (FEED) of MgO/ MWCNTs are investigated. The I–V curves for these MgO/MWCNTs exhibited a bump in the middle of the curve which may be caused by the existence of a MgO insulating layer. The FEED for these coated MWCNTs showed one or two peak(s) depending on whether the MgO/MWCNT sample was aged or not. The field emission from different MgO/ MWCNTs with different tip radii may be responsible for this FEED peak behavior. r 2002 Elsevier Science B.V. All rights reserved.
01/2002; 293090(79).
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Segi Yu,
Sunghwan Jin,
Whikun Yi,
Jeongho Kang,
Taewon Jeong,
Yongsoo Choi, Jeonghee Lee,
Jungna Heo,
Nae Sung,
Ji-Beom Yoo,
Min Jong,
Kim
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ABSTRACT: The characteristics of a field emission display (FED), which is based on an undergate-type triode carbon nanotube (CNT), have been examined by incorporating an electron-multiplying microchannel plate (MCP) between the anode and cathode plates of a FED. The MCP was fabricated by electroless plating and the sol–gel process on punched alumina. By applying appropriate voltages between the two faces of an MCP within a FED, the current at the anode plate of a FED was found to be enhanced more than three to five times, leading to higher brightness. The focusing of field emitted electrons was also improved by adjusting the bottom voltage of the MCP, which resulted in a clear image. Therefore, the incorporation of the MCP improved the performance of an undergate-type CNT FED, which can now be considered as one of the key candidates for flat panel displays.
Jpn. J. Appl. Phys. The Japan Society of Applied Physics. 11/2001; 40(1):6088-6091.
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ABSTRACT: Three series of MgO thin films were prepared by the spin coating of MgO precursor solutions (aqueous and organic based solutions) and by electron-beam evaporation. The quality of the films coated on the Si (100) substrate was characterized by observing crystallinity and surface roughness of the films. The measurement of the secondary electron emission (SEE) yield of the MgO films does not reveal any significant dependence on the MgO film fabrication process. However, it was found that the magnitude of the SEE yield is strongly dependent on the sample bias voltage. The maximum SEE yield of over 6 was obtained for the films prepared by both aqueous and organic based solutions. MgO layer formation by precursor solutions is a promising method considering the fact of its easiness and convenience, which also gives a relatively large SEE yield comparable to the MgO layer prepared by electron-beam evaporation. © 2001 American Vacuum Society.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/2001; · 1.34 Impact Factor
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Whikun Yi,
SeGi Yu,
Wontae Lee,
In Taek Han,
Taewon Jeong,
Yoonseong Woo, Jeonghee Lee,
Sunghwan Jin,
Wonbong Choi,
Jungna Heo,
Dongryul Jeon,
J. M. Kim
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ABSTRACT: Enormously high secondary electron emission yields under electric field are observed from MgO deposited on carbon nanotubes. The yields reach a value as high as 15 000 and are strongly dependent upon the bias voltage applied to the sample. The creation of the electric field across the MgO film after bombardment of primary electrons is considered as one of key features, since positive charges are generated at the surface by departure of secondary electrons. Subsequent bombarding electrons produce other secondary electrons inside the MgO film, then the liberated secondaries are accelerated towards the surface under the strong field. Under this condition, the secondary electrons gain sufficient energy to create further electrons by impact ionization. The process continues until an equilibrium avalanche is established. To elucidate the earlier explanations, the kinetic energy spectra of secondary electrons are measured by an energy analyzer at various bias voltages in MgO/carbon nanotube samples. The analysis of spectral results with the energy band diagram gives us strong evidence for the suggested mechanism. © 2001 American Institute of Physics.
Journal of Applied Physics 03/2001; 89(7):4091-4095. · 2.17 Impact Factor
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ABSTRACT: Field emission is measured for various multiwalled carbon nanotubes (CNTs) prepared from chemical vapor deposition (CVD) methods or metal-(or glass-) pasted printing techniques. Among the samples, the thermal CVD grown CNT and silver-pasted CNT samples show enhanced electron emissions upon laser light irradiation corresponding to the wavelengths of 266 and 532 nm. The reasons behind this behaviour are explained in this paper
Vacuum Microelectronics Conference, 2001. IVMC 2001. Proceedings of the 14th International; 02/2001
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ABSTRACT: We have developed a novel microchannel plate (MCP) by introducing new materials and process technologies. The key features of our MCP are summarized as follows: (i) bulk alumina as a substrate, (ii) the channel location defined by a programmed-hole puncher, (iii) thin film deposition by electroless plating and/or sol–gel process, and (iv) an easy fabrication process suitable for mass production and a large-sized MCP. The characteristics of the resulting MCP have been evaluated with a high input current source such as a continuous electron beam from an electron gun and Spindt-type field emitters to obtain information on electron multiplication. In the case of a 0.28 μA incident beam, the output current enhances ∼170 times, which is equal to 1% of the total bias current of the MCP at a given bias voltage of 2600 V. When we insert a MCP between the cathode and the anode of a field emission display panel, the brightness of luminescent light increases 3–4 times by multiplying the emitted electrons through pore arrays of a MCP. © 2000 American Institute of Physics.
Review of Scientific Instruments 10/2000; 71(11):4165-4169. · 1.37 Impact Factor
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ABSTRACT: The efficiency of a field emission display was improved significantly with a newly developed microchannel plate. The key features of this unit and its fabrication are summarized as follows: (a) bulk alumina is used as a substrate material, (b) channel location is defined by a programed-hole puncher, and (c) thin film deposition is conducted by electroless plating followed by a sol–gel process. With the microchannel plate between the cathode and the anode of a field emission display, the brightness of luminescent light increases three- to fourfold by electron multiplication through an array of pores in the device. In addition, the fabricated microchannel plate prevents spreading of electrons emitted from the cathode tips, thus improving both display resolution and picture quality. © 2000 American Institute of Physics.
Applied Physics Letters 09/2000; 77(11):1716-1718. · 3.84 Impact Factor
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ABSTRACT: Two series of MgO thin layers having various thicknesses were prepared on the Si substrate by electron-beam evaporation and by spin coating of MgO precursor solutions. We found that the magnitude of the secondary electron emission (SEE) yield of the MgO films strongly depends on the film thickness and the sample bias voltage. We ascribed it to the electric field through the insulating MgO layer, which allowed fast supply of electrons from the Si substrate to the surface. The mechanism of electron supply can be explained either as an acceleration through the MgO layer that becomes partially conductive upon primary electrons bombardment (radiation induced conductivity), or as a tunneling through the non-irradiated region of the insulating layer where the primary electrons cannot reach deeply into the sample with a certain penetration depth. The maximum SEE yield of the each MgO film on the Si substrate was observed when the penetration depth of primary electrons was close to the thickness of the MgO film, if the applied electric potential to the sample was low. Under a strong electric potential, the relationship between the penetration depth of primary electrons and the thickness of MgO films is not observed. It suggests the existence of the non-irradiated region, where electron supply is allowed by electron tunneling. Therefore, the magnitude of SEE yield for the thin insulating layer is strongly related to the detailed mechanism of electron supply, which is determined by the thickness of the insulating layer and the applied bias voltage to the sample during the SEE process.
Applied Surface Science.
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Jeonghee Lee,
Taewon Jeong,
Jungna Heo,
Shang-Hyeun Park,
DongHun Lee,
Jong-Bong Park,
HyoukSoo Han,
YoungNam Kwon,
Igor Kovalev,
Seon Mi Yoon,
Jae-Young Choi,
Yongwan Jin,
Jong M. Kim,
Kay Hyeok An,
Young Hee Lee,
SeGi Yu
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ABSTRACT: A cryogenic crushing method to produce short carbon nanotubes (CNTs) is described. Crushing CNTs at liquid nitrogen temperature allows them to be shortened and make them appreciably soluble in a solvent without any dispersant. Typical lengths of less than 500 nm were obtained from 30 min crushing. The CNTs were characterized using atomic force microscopy, thermogravimetric, and Raman analyses.
Carbon.
