Ki Nam Yun

Field emission properties from flexible field emitters using carbon nanotube film

Flexible carbon nanotube (CNT) field emitters are fabricated using CNT films on polyethylene terephthalate films. The flexible CNT emitters, which are made using double-walled CNTs, show high emission performance and also indicate stable field emission properties under several bending conditions. The flexible CNT emitters have a low turn-on field of about 0.82 V/μm and a high emission current density of about 2.0 mA/cm2 at an electric field of 1.6 V/μm. During stability tests, the flexible CNT emitters initially degrade over the first 4 h but exhibit no further significant degradation over the next 16 h testing while being continually bent. A flexible lamp made using the flexible CNT emitter displays uniform and bright emission patterns in a convex mode.

Percolated pore networks of oxygen plasma-activated multi-walled carbon nanotubes for fast response, high sensitivity capacitive humidity sensors

We report on the preparation of capacitive-type relative humidity sensors incorporating plasma-activated multi-wall carbon nanotube (p-MWCNT) electrodes and on their performance compared with existing commercial technology. Highly open porous conductive electrodes, which are almost impossible to obtain with conventional metal electrodes, are fabricated by spray-depositing MWCNT networks on a polyimide layer. Oxygen plasma activation of the MWCNTs is also explored to improve the water adsorption of the MWCNT films, by introducing oxygen-containing functional groups on the CNT surface. Polyimide humidity sensors with optimized p-MWCNT network electrodes exhibit exceptionally fast response times (1.5 for adsorption and 2 s for desorption) and high sensitivity (0.75 pF/% RH). These results may be partially due to their percolated pore structure being more accessible for water molecules, expending the diffusion of moisture to the polyimide sensing film, and partially due to the oxygenated surface of p-MWCNT films, allocating more locations for adsorption or attraction of water molecules to contribute to the sensitivity.

High-performance carbon nanotube thin-film transistors on flexible paper substrates

Single-walled carbon nanotubes (SWCNTs) are promising materials as active channels for flexible transistors owing to their excellent electrical and mechanical properties. However, flexible SWCNT transistors have never been realized on paper substrates, which are widely used, inexpensive, and recyclable. In this study, we fabricated SWCNT thin-film transistors on photo paper substrates. The devices exhibited a high on/off current ratio of more than 106 and a field-effect mobility of approximately 3 cm2/V·s. The proof-of-concept demonstration indicates that SWCNT transistors on flexible paper substrates could be applied as low-cost and recyclable flexible electronics.

Ferromagnetic properties of single walled carbon nanotubes doped with manganese oxide using an electrochemical method

We report the ferromagnetic doping of single walled carbon nanotubes (SWCNTs) using an electrochemical method. Ferromagnetism was well defined at the low temperature region and the Curie temperature was above 350 K. The coercive field increases monotonically with the increasing manganese concentration. Improved ferromagnetism with the increasing of manganese concentration and the control of hysteresis has been observed, and the electrical transport measurement of SWCNTs shows the normal semiconductor properties. These investigations indicate the great potential of SWCNTs in applications such as spin electronics.

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 6.34 mA (1.6 A/cm2) under an applied electric field of 5.3 V/μm. It also indicates good long-term emission stability, which reveals no degradation in the emission current for 20 h. 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.

Excellent oxidation endurance of boron nitride nanotube field electron emitters

Boron nitride nanotubes (BNNTs) are considered as a promising cold electron emission material owing to their negative electron affinity. BNNT field emitters show excellent oxidation endurance after high temperature thermal annealing of 600 °C in air ambient. There is no damage to the BNNTs after thermal annealing at a temperature of 600 °C and also no degradation of field emission properties. The thermally annealed BNNTs exhibit a high maximum emission current density of 8.39 mA/cm2 and show very robust emission stability. The BNNTs can be a promising emitter material for field emission devices under harsh oxygen environments.

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.

High-Performance Field-Emission Properties of Boron Nitride Nanotube Field Emitters

Boron nitride nanotubes (BNNTs) have attracted considerable attention as a field emission material because of their high mechanical strength, high negative electron affinity, and high oxidation resistance. Nevertheless, the obtained field-emission properties of BNNTs have indicated poor emission performance, which is a very high turn-on electric field with a low emission current. We fabricated BNNT field emitters and investigated their field-emission properties. The field-emission properties of the BNNT field emitters were considerably enhanced compared to those of other BN nanomaterial-based field emitters. The turn-on and the threshold electric fields of the BNNT field emitter were 3.1 and 5.4 V/μm at the gap distance of 750 μm, respectively. Both the turn-on and the threshold electric fields of the BNNT field emitters were decreased by increasing the gap distance between the emitter tip and the anode electrode. Degradation of the emission current during field emission operation for 20 h showed no significant difference according to the gap distance. Emission current fluctuation of the BNNT field emitters showed that the smaller gap was more unstable than the larger gap. The enhanced emission properties are mainly attributed to the small diameter, high-quality, and straight structure of BNNTs as well as the stable network formation of the BNNT film with good mechanical and electrical contact between the BNNTs and the cathode electrode. The remarkable emission performance of the BNNT field emitters might have promising applications for various field-emission devices.

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.

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.