In Taek Han

FULLY SEALED, HIGH-BRIGHTNESS CARBON-NANOTUBE FIELD-EMISSION DISPLAY

A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415 °C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V/μm and field emission current of 1.5 mA at 3 V/μm (J=90 μA/cm2) were observed. Brightness of 1800 cd/m2 at 3.7 V/μm was observed on the entire area of a 4.5 in. panel from the green phosphor-indium–tin–oxide glass. The fluctuation of the current was found to be about 7% over a 4.5 in. cathode area.

Application of carbon nanotubes to field emission displays

Abstract Large-area field emission displays were fabricated with single-wall carbon nanotube emitters. A carbon nanotube paste was prepared and screen-printed to form an electron emission layer on a glass-based substrate. Carbon nanotube-based field emission displays fabricated by thick film processing were successfully integrated to demonstrate moving color images. They revealed excellent field emission characteristics of a threshold electric field of approximately 2 V/μm. We have also investigated triode-type field emission display structures to achieve high-gray scale and high brightness. In the triode structure, it was observed that electron emission from carbon nanotube emitters was controlled by modulation of gate voltages.

Fabrication and characterization of gated field emitter arrays with self-aligned carbon nanotubes grown by chemical vapor deposition

Field emitter arrays with multiwall carbon nanotubes (CNTs) grown inside their gated holes were fabricated on glass substrates. The Fe–Ni–Co alloy catalyst dots on which the CNTs would be grown were deposited into the gated holes by a self-aligned method to maintain a constant distance between CNT emitters and gate electrodes. The CNTs were synthesized by thermal chemical vapor deposition using a gas mixture of CO and H2 at 500 °C. The CNT lengths were controlled by changing ratios of CO to H2. Field emission currents and images were monitored as a function of gate and anode voltages. It was shown that the CNT emitters grown just up to the gate electrode height operated best in a triode mode.

Low temperature synthesis of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition

Abstract We have synthesized pure carbon nanotubes at very low temperature using microwave plasma-enhanced chemical vapor deposition (MPECVD) with methane/hydrogen gas. Ratio of a gas mixture (CH4/H2) and deposition time at a substrate temperature below 520°C are optimized. Pure and dense carbon nanotubes are grown uniformly over a large area of Ni-coated silicon substrates without any pretreatment of substrates. The diameters and lengths of carbon nanotubes could be controlled by changing the ratio of gas mixture and the growth time. Raman spectrum clearly shows the peak at 1592 cm−1 (G-band), indicating the formation of graphitized carbon nanotubes.

In situ diagnosis of chemical species for the growth of carbon nanotubes in microwave plasma-enhanced chemical vapor deposition

Abstract A synthesis of multi-wall carbon nanotubes (MWNTs) by microwave plasma-enhanced chemical vapor deposition using CH 4 /H 2 /NH 3 gases on Ni/Cr-coated glass at low temperature, was investigated by optical emission spectroscopy (OES) and quadrupole mass spectroscopy (MS). It was observed that the MWNTs were grown within a very restrictive range of the gas compositions. Optical emission lines were observed primarily from atomic hydrogen H α , molecular hydrogen, and CN radicals. The quadrupole mass spectrum also showed the formation of C 2 H 2 and HCN. An addition of a small amount of NH 3 resulted in a decrease of C 2 H 2 , which could be used to estimate amounts of carbon sources present in the plasma for the growth of MWNTs, and increases of CN and H α radicals acting as etching species of amorphous carbon. These results show that the etching species of amorphous carbon as well as the growth species are necessary and the ratio between two species have to be in appropriate condition for the synthesis of carbon nanotubes at low temperature. The optimum C 2 H 2 /H α ratio in the gas mixture for the growth of MWNTs at low temperature was found to be 1:5 in this study.

Paper as a Substrate for Inorganic Powder Electroluminescence Devices

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.

Cyclic technique for the enhancement of highly oriented diamond film growth

Abstract Diamond films have been deposited on (100) Si substrates through carburization, nucleation and growth steps using a microwave plasma-enhanced chemical vapor deposition system. The surface morphologies of the films were investigated as a function of the carburization time. It is likely that the ball-like agglomerates observed on the carburized surface act as nucleation sites for diamond. We also found that the density of agglomerates is not dependent on the carburization time, but their size increases with increasing carburization time. A cyclic process was applied during either the nucleation or the growth step. In general, the cyclic process leads to a decrease in the density of large agglomerates produced during the carburization step. Furthermore, the {100}-oriented texture growth is enhanced and the coverage area is increased by applying the cyclic process during nucleation.

Secondary electron emission yields from MgO deposited on carbon nanotubes

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...

Tip growth model of carbon tubules grown on the glass substrate by plasma enhanced chemical vapor deposition

Morphology of Ni tips and microstructures of carbon tubules were investigated and a growth model for carbon tubules was proposed. Triangular shaped Ni tips and piled-cone structure of carbon tubules were observed at the growth temperature of 500 °C. At the high growth temperature of 620 °C, smoothened edge shaped Ni tips were found and graphite layers became parallel to the growth direction as they were close to the outer wall of carbon tubules. Formation of Ni nuclei for carbon tubule growth was explained by NH3 pre-etching and precipitation of carbon atoms diffused from the surface of the Ni layer. A preferential growth of carbon tubules was observed and explained with the Ni orientation and size effect. A modified tip growth model based on surface diffusion was proposed for the growth mechanism of carbon tubules.

Low temperature growth of multi-wall carbon nanotubes assisted by mesh potential using a modified plasma enhanced chemical vapor deposition system

Abstract Well-aligned carbon nanotubes have been synthesized on Corning and silicon substrates at extremely low temperatures of 450 °C using a slightly modified conventional plasma enhanced chemical vapor deposition (PECVD). The deposition system was intentionally designed to impose mesh potential on the substrates through an external electrode that was a critical parameter for low temperature growth. Mixture gases of C2H2 and NH3 with the imposed mesh potential of about 50 V effectively aligned multi-wall carbon nanotubes at 450 °C on Ni-coated substrates.