Jeungchoon Goak

Wear Behavior of Functionalized Multi-walled Carbon Nanotube Reinforced Epoxy Matrix Composites

This article studies the tribological behavior of functionalized multi-walled carbon nanotubes (MWNTs) reinforced epoxy matrix composites. MWNTs reinforced epoxy composites are fabricated by an injection molding process. The effects on the tribological properties of different loading concentrations and different functional groups of MWNTs are investigated by using a linear reciprocal wear tester. As increasing the concentration of MWNTs reduces wear loss, better tribological property was attained on functionalized MWNTs than as-produced MWNTs. The changes in worn surface morphology are observed in order to investigate the wear behavior. The MWNTs in the epoxy matrix near the surface are exposed and became a lubricating working film on the worn surface. The dispersion and interfacial bonding of MWNTs in the epoxy matrix are investigated from the fracture surface. The existence of MWNT at the wear surface is verified by a Raman spectrometer.

Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy

Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.

Improvement of field emission characteristics of carbon nanotubes by enhancing physical and electrical contacts

We developed a novel process to fabricate point-type carbon nanotube (CNT) emitters formed by transferring a CNT film onto a Ni-coated Cu wire with a diameter of 1.24 mm. A Ni layer plays a role in enhancing the adhesion of CNTs to the substrate and improving their electrical resistance and field emission characteristics. On firing at 400 °C, CNTs appear to directly bonded to a Ni layer. With a Ni layer introduced, a turn-on electric field of CNT emitters decreases from 1.73 to 0.81 V/μm by firing. The CNT film on the Ni-coated wire produces a high emission current density of 667 mA/cm2 at quite a low electric field of 2.87 V/μm.

3.5: Fabrication and field emission properties of point-type emitters of carbon nanotubes for miniaturized X-ray sources

We developed a simple process to fabricate point-type CNT emitters by repeatedly coating CNT films with controlled nanotube morphologies and strong adhesion. The CNT emitters produced significantly large field emission current densities at very low electric fields and excellent long-term stability for high current emission. The fabrication processes and characteristics of the CNT electron sources for high-resolution miniaturized X-ray tubes will be presented in detail.

Quantitative study on the effect of residual gas species on the electron emission properties of carbon nanotubes

Ever since the invention of the carbon nanotube (CNT) based field emission electron source, there has been much effort to investigate novel techniques to achieve more efficient and more reliable sources. Although advances in the CNT electron source technology have leaded to a considerable improvement in a wide range of applications including flat-panel displays, backlight units of liquid crystal displays, microwave amplifiers, portable X-ray tubes, spacecraft propulsion systems, etc., several obstacles, in particular, lifetime of CNT emitters, still remain to be overcome for commercialization. Among many factors affecting the lifetime of CNT emitters working in vacuum, residual gases inside a panel would be one of the most crucial causes, especially when the CNT emitters are made from the organic vehicle-based paste. The residual gases can cause a catastrophic damage to the vacuum microelectronic devices by electrical arcing or ion bombardment onto the cathode plate.

Transparent field emitters fabricated with ultra-thin single walled carbon nanotubes

Carbon nanotubes (CNTs) with superior chemical, electrical, and mechanical properties have been actively studied for a wide range of applications.[1] In particular, their applications to field emission devices including backlight units of liquid crystal display, lighting lamps, X-ray source, microwave amplifiers, electron microscopes, etc., have been strongly pursued because of their geometric merits of allowing low-voltage electron emission such as a large aspect ratio and a small radius of curvature at tip. [2] In this study, we fabricated a transparent cathode back plate by depositing an ultra-thin film of single walled CNTs (SWCNTs) on an indium tin oxide (ITO)-coated glass substrate. First, an aqueous CNT solution was prepared by ultrasonically dispersing purified SWCNTs in deionized water with sodium dodecyl sulfate (SDS). After centrifugation, several milliliters or even a hundred of microliters of the well-dispersed CNT solution was deposited onto a porous alumina membrane through vacuum filtration. Thereafter, the alumina membrane was solvated with the 3 M NaOH solution and the floating CNT film was easily transferred to an ITO glass substrate in an area of 1 cm diameter defined by using a film mask. The CNT film was subjected to an activation process with an adhesive roller, standing the CNTs up to serve as electron emitters. Figures 1 and 2 show that the turn-on voltages of the CNT emitters were lowered, and their field enhancement factors became higher, respectively, as increasing the volume of the CNT solution used to prepare the CNT emitter samples. For display applications, field emission devices are configured in such a way that the phosphor anode (front plate) is placed against the CNT emitters (back plate). In most cases, light, which is generated from the phosphor, passes through the anode front plate to reach observers.[3] When electrons bombard onto the phosphor particles whose diameters are usually in a range of several micrometers, light is produced only in a narrow depth of the surface of the phosphor particles due to a limited penetration depth of electrons. During the transmission through the phosphor layer, a light intensity considerably decreases by scattering. In this case, we observe only a portion of light emitted from the phosphor. First, two types of phosphor anode plates were engaged: a phosphor layer screened on an ITO glass substrate and a phosphor layer screened on a Crcoated glass substrate. For the former type of a phosphor plate, light was observed on both the front side (case 1) and the back side (case 2), where brightness on the back was ~13% higher than that on the front in our experiments. For the latter type of a phosphor plate, however, light was observed only on the cathode back side as the Cr layer on the anode glass served as a reflecting mirror (case 3), improving the light brightness as much as ~56% compared with that of the case 1. Secondly, we formed an Al reflecting layer on a cathode plate by which all lights pass through only the anode front plate (case 4), showing an increase of luminance but smaller than the case 3. Luminance variations for these four cases of device configurations are given in Fig. 3. This study demonstrated the lamps emitting light on the both sides by using transparent CNT films, but showed that reflecting all lights through the cathode back side exhibited the highest brightness.