Seok Gy Jeon

Fabrication of carbon nanotube emitters on the graphite rod and their high field emission performance

Carbon nanotube (CNT) emitters with small emission area were fabricated on graphite rods using CNT films. By introducing the edge polishing process, the field emission performance of the CNT emitter was much improved, which showed a very high emission current of 6.34u2009mA (1.6u2009A/cm2) under an applied electric field of 5.3u2009V/μm. It also indicates good long-term emission stability, which reveals no degradation in the emission current for 20u2009h. The emission patterns demonstrate uniform and well-focused electron beam spots. The enhanced field emission performance is mainly attributed to the suppressed edge emission after the edge polishing process.

Field emission behavior of carbon nanotube field emitters after high temperature thermal annealing

The carbon nanotube (CNT) field emitters have been fabricated by attaching a CNT film on a graphite rod using graphite adhesive material. The CNT field emitters showed much improved field emission properties due to increasing crystallinity and decreasing defects in CNTs after the high temperature thermal annealing at 900 °C in vacuum ambient. The CNT field emitters showed the low turn-on electric field of 1.15 V/μm, the low threshold electric field of 1.62 V/μm, and the high emission current of 5.9 mA which corresponds to a current density of 8.5 A/cm2. In addition, the CNT field emitters indicated the enhanced field emission properties due to the multi-stage effect when the length of the graphite rod increases. The CNT field emitter showed good field emission stability after the high temperature thermal annealing. The CNT field emitter revealed a focused electron beam spot without any focusing electrodes and also showed good field emission repeatability.

Excellent field emission properties from carbon nanotube field emitters fabricated using a filtration-taping method

Abstract A filtration-taping method was demonstrated to fabricate carbon nanotube (CNT) emitters. This method shows many good features, including high mechanical adhesion, good electrical contact, low temperature, organic-free, low cost, large size, and suitability for various CNT materials and substrates. These good features promise an advanced field emission performance with a turn-on field of 0.88 V/mm at a current density of 0.1 mA/cm 2 , a threshold field of 1.98 V/mm at a current density of 1 mA/cm 2 , and a good stability of over 20 h. The filtration-taping technique is an effective way to realize low-cost, large-size, and high-performance CNT emitters. Key words: field emission properties, carbon nanotube, filtration-taping method 1. Introduction Due to their unique geometry and physical properties, carbon nanotubes (CNTs) are currently being investigated as next-generation field emitter materials for cold cathodes. Numerous papers can be found on field emission applications such as field emission displays, lamps, X-ray sources, high-resolution electron-beam instruments, and microwave amplifiers [1-5]. Up to now, various techniques have been developed for fabricating CNT field emitters using as-grown, spraying, electrophoresis, screen-printing, and attaching individual CNTs on tungsten probe methods, etc. [6-10]. However, these techniques suffer from weak me-chanical adhesion between CNT emitters and the cathode, or severe degradation of CNT emitters due to the organic binders used in the process, which lead to a short lifetime. There-fore, an efficient and organic binder-free technique for fabricating CNT emitters is still a great challenge. In this letter, we demonstrate an advanced organic-free technique named the filtration-taping method. The filtration-taping method is suitable to fabricate simple, large, and cost-effective CNT emitters that can ensure a high mechanical adhesion, good electri-cal contact, and damage-free CNT tips, resulting in enhanced field emission properties and excellent stability.

Field emission properties of carbon nanotube emitters dependent on electrode geometry

Field emission properties of carbon nanotube (CNT) emitters dependent on electrode geometry have been systematically studied using two different types of diode electrode configurations. The experimental and simulation results clearly reveal that field emission properties, such as emission current and long-term emission stability, are strongly influenced by the geometry of the electrode configuration. The enhanced local electric field at the periphery of CNT emitters results in high local edge emissions that severely degrade emission current during long-term emission stability test and reduce the emission current density before electrical breakdown.

Extremely high emission current from carbon nanotube point emitter

We demonstrated a novel point-typed carbon nanotube field emitters using a triangular-shaped carbon nanotube films. We also investigated the field emission properties of the field emitters according to the tip angles. The wider field emitters exhibited higher emission current, and the field emitters with a tip angle of 120° showed extremely high emission current density over 104 A/cm2 (> 10 mA) at a low electric field of 1.24 V/μm.

Precise Patterning of Organic Single Crystals via Capillary-Assisted Alternating-Electric Field

Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low-cost and high-performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high-throughput, high-precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary-assisted alternating-electric field method for the large-scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm2 . The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible-blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high-integration, high-performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals.

Sheet electron beam from line-shape carbon nanotube field emitters

A sheet electron beam source is demonstrated using a line-shape carbon nanotube (CNT) field emitter. The line-shape CNT field emitter shows large emission current under the small applied voltage. Moreover, the emitted electron is well-confined without any focusing lens.

Silicon based micro-scale metal grid for field emission device

For application to electron field emission devices, a metal grid based on a silicon frame is introduced. Silicon frame is used to improve the thermal resistivity and electrical stability by electron beam. Silicon based micro-scale metal grid fabricated using MEMS technology.

Silicon-based metallic micro grid for electron field emission

A micro-scale metal grid based on a silicon frame for application to electron field emission devices is introduced and experimentally demonstrated. A silicon lattice containing aperture holes with an area of 80 × 80 µm2 and a thickness of 10 µm is precisely manufactured by dry etching the silicon on one side of a double-polished silicon wafer and by wet etching the opposite side. Because a silicon lattice is more rigid than a pure metal lattice, a thin layer of Au/Ti deposited on the silicon lattice for voltage application can be more resistant to the geometric stress caused by the applied electric field. The micro-fabrication process, the images of the fabricated grid with 88% geometric transparency and the surface profile measurement after thermal feasibility testing up to 700 °C are presented.

Field emission properties of point emitters fabricated using carbon nanotubes on the graphite rod

We demonstrated field emission properties of a CNT point emitter fabricated by using CNTs on a graphite rod. The emitter has the highest current of 6.3 mA; the corresponding current density is 1.6 A/cm2. The emitter is stable at a current of 0.1 mA for 20 hours. It also showed a small and uniform emission pattern at the phosphor coated ITO glass. Our point emitter could be a good candidate for X-ray source applications.