Wal Jun Kim

Enhancement of heating performance of carbon nanotube sheet with granular metal.

A strategy for enhancing the heating performance of freestanding carbon nanotube (CNT) sheet is presented that involves decorating the sheet with granular-type palladium (Pd) particles. When Pd is added to the sheet, the heating efficiency of CNT sheet is increased by a factor of 3.6 (99.9 °C cm(2)/W vs 27.3 °C cm(2)/W with no Pd). Suppression of convective heat transfer loss attributes to the enhanced heat generation efficiency. However, higher heating response of CNT/Pd sheet was observed compared to CNT sheet, hence suggesting that the electron-lattice energy exchange could be additional heating mechanism in the presence of granular-type particles of Pd having a diameter of 10 nm or less. CNT sheet/Pd is quite stable, retaining its initial characteristics even after 300 cycles of on-off voltage pulses and shows fast thermal responses of the heating and cooling rates being 154 and -248 °C/s, respectively.

Synthesis and field emission characteristics of carbon nanocoils with a high aspect ratio supported by copper micro-tips

Carbon nanocoils (CNCs) were synthesized via thermal chemical vapour deposition (CVD) with C2H2 and NH3 gases at 600 °C. A Ni catalyst was placed upon the copper micro-tip structures that were fabricated on a silicon substrate. Our CNCs had a long rope shape with a length not exceeding 100 µm and a nanoscale diameter. The copper micro-tips were formed through high current pulse electroplating, which played a significant role in characterizing our CNCs. The CNCs grown on the copper micro-tips showed outstanding field emission performance and long-term stability. Their turn-on field, defined as that at a current density of 10 µA cm−2, was 1.30 V µm−1 and the maximum current density reached 11.17 mA cm−2 at an electric field of 2.39 V µm−1.

Better than 10 mA Field Emission from an Isolated Structure Emitter of a Metal Oxide/CNT Composite

An isolated structure emitter is presented that can deliver a field emission better than 10 mA, a level that is by far the highest ever reported. A composite of CNT (carbon nanotube) and WO(3) is used to grow the point emitter by a crystal-like growth technique. The head of the grown needle that is the emitter is removed by electric discharge machining (EDM). The EDM treatment not only controls the length of the emitter as desired but also makes the tip of the emitter uniform. The thermal heat due to EDM treatment leads to the formation of a tungsten carbide phase, which results in a 3 orders of magnitude reduction in contact resistance. The point emitter is robust in its stability, as evidenced by its on-time resilience against a severe bias test.

Fabrication and the enhanced emission uniformity of carbon nanofibers using a glass cap

Uniformity is one of the most important qualifications for reliable field emission devices based on carbon nanofibers (CNFs). We synthesized CNFs by thermal chemical vapor deposition at 600 °C on the glass substrate, promising practical large-area applications. A glass cap was introduced to enhance the uniformity of CNF emitters vertically grown under the guidance of micro-grooves, which provided passages for the diffusion of precursor gas to CNF growth sites. Our CNFs, vertically leveled by the glass cap with the support of the micro-grooves, and without any post-treatments, showed excellent uniformity in field emission as well as long-term stability.

Electron Beam Sources Based on Carbon Nanotube for THz Applications

Performance of electron emitter plays an essential role in the detection and generation of electromagnetic wave signals. It becomes technologically challenging from spanning terahertz applications, due to the lack of sufficient power sources. The vacuum THz amplifier, such as a travelling wave tube or a klystron is practically used to increase the output power. The characteristic of these amplifiers is mainly represented by the performance of electron beam source which has to deliver a sufficient current in order to allow an amplification of the THz signal.

Fabrication of field emitters with triboelectricity

Triboelectricity method for fabrication of carbon nanotube field emitters using indirect attachment was researched in this paper. Triboelectricity method is able to avoid secondary contaminations due to residues of adhesives because it does not use any adhesive. In order to confirm existence of factional electricity, surface potential is measured with electrostatic voltimeter.

Electrical discharge machining of carbon nanomaterials: Mechanisms and the advanced field emission applications

Carbon nanomaterials such as carbon nanotubes and carbon nanofibers (CNFs) have been intensively investigated for various nanoelectronic applications due to their superb properties, good stability, and high aspect ratio. There have been many efforts to develop flat panel displays, light sources, and backlight units by using carbon nanomaterials. For wider applications, carbon nanomaterials often need to be cut, leveled, patterned, and figured. A reliable and precise micro-machining process, electrical discharge machining (EDM), was investigated in depth as a very neat method for the effective and multifunctional engineering of carbon nanomaterials. In the present study, the mechanisms of the EDM engineering of carbon nanomaterials are systematically examined, and the advanced field emission applications derived from the EDM method are presented.