Naesung Lee

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.

Electrophoresis deposition of carbon nanotubes for triode-type field emission display

A triode-type field emission display has been fabricated using carbon nanotube emitters. Purified single walled carbon nanotubes were selectively deposited onto a cathode electrode in a triode-type structure by an electrophoresis. Emission current was modulated with gate potentials of 100–300 V. A high brightness of 1000 cd/m2 with uniform emission was obtained at 900 V at the anode and 200 V at the gate. The fluctuation of emission current was found to be less than 5% in a fully sealed field emission display. Selective deposition of carbon nanotubes by electrophoresis shows high feasibility for triode-type field emission displays.

Controlling the diameter, growth rate, and density of vertically aligned carbon nanotubes synthesized by microwave plasma-enhanced chemical vapor deposition

Vertically aligned carbon nanotubes were synthesized on Ni-deposited Si substrates using microwave plasma-enhanced chemical vapor deposition. The grain size of Ni thin films varied with the rf power density during the rf magnetron sputtering process. We found that the diameter, growth rate, and density of carbon nanotubes could be controlled systematically by the grain size of Ni thin films. With decreasing the grain size of Ni thin films, the diameter of the nanotubes decreased, whereas the growth rate and density increased. High-resolution transmission electron microscope images clearly demonstrated synthesized nanotubes to be multiwalled.

Synthesis of aligned carbon nanotubes using thermal chemical vapor deposition

Aligned carbon nanotubes have been synthesized on transition metal-coated silicon substrates with C2H2 using thermal chemical vapor deposition. It was found that nanotubes can be mostly vertically aligned on a large area of plain Si substrates when the density of metal domains reaches a certain value. Pretreatment of Co–Ni alloy by HF dipping and etching with NH3 gas prior to the synthesis is crucial for vertical alignment. Steric hindrance between nanotubes at an initial stage of growth forces nanotubes to align vertically. Nanotubes are grown by a catalyst-cap growth mechanism. Applications to field emission displays are demonstrated with emission patterns.

Comparison of frictional forces on graphene and graphite

We report on the frictional force between an SiN tip and graphene/graphite surfaces using lateral force microscopy. The cantilever we have used was made of an SiN membrane and has a low stiffness of 0.006 N m(-1). We prepared graphene flakes on a Si wafer covered with silicon oxides. The frictional force on graphene was smaller than that on the Si oxide and larger than that on graphite (multilayer of graphene). Force spectroscopy was also employed to study the van der Waals force between the graphene and the tip. Judging that the van der Waals force was also in graphite-graphene-silicon oxide order, the friction is suspected to be related to the van der Waals interactions. As the normal force acting on the surface was much weaker than the attractive force, such as the van der Waals force, the friction was independent of the normal force strength. The velocity dependency of the friction showed a logarithmic behavior which was attributed to the thermally activated stick-slip effect.

Synthesis of uniformly distributed carbon nanotubes on a large area of Si substrates by thermal chemical vapor deposition

We have synthesized carbon nanotubes by thermal chemical vapor deposition of C2H2 on transition metal-coated silicon substrates. Multiwalled carbon nanotubes are uniformly synthesized on a large area of the plain Si substrates, different from previously reported porous Si substrates. It is observed that surface modification of transition metals deposited on substrates by either etching with dipping in a HF solution and/or NH3 pretreatment is a crucial step for the nanotube growth prior to the reaction of C2H2 gas. We will demonstrate that the diameters of carbon nanotubes can be controlled by applying the different transition metals.

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.

Field emission from 4.5 in. single-walled and multiwalled carbon nanotube films

Field emission properties of 4.5 in. flat panel displays in a diode type panel using single-walled (SWNTs) and multiwalled carbon nanotube tips (MWNTs) were characterized and compared. The panel, fabricated by a slurry squeezing and surface rubbing technique, enables the generation of more emission sites by removing materials on the surface. The turn-on field of MWNTs decreased from 6.4 to 3 V/μm by treatment of the surface, and that of SWNTs also decreased, from 4.5 to 2 V/μm. The density of aligned MWNTs is approximately 2/μm2, whereas the aligned SWNTs were uniformly distributed, with densities of 5–10/μm2. As a result, SWNT films show higher emission uniformity than MWNT films. A gradual degradation over time was observed in both MWNTs and SWNTs. The current stability curve of the SWNTs decreased about 20%, while that of the MWNTs decreased less than 10%.

Growth of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition at low temperature

Carbon nanotubes have been grown on Ni-coated Si substrates by microwave plasma-enhanced chemical vapor deposition with a mixture of methane and hydrogen gases at temperatures ranging from 520 to 700 °C. The density and the length of the carbon nanotubes increased with increasing growth temperature. At a growth temperature of 520 °C, the carbon nanotubes were curly, whereas the nanotubes were straight and self-aligned upward at temperatures above 600 °C. Images from high-resolution transmission electron microscopy showed that the nanotubes were multiwalled, with a few wall structures. The graphitized structures were also confirmed by Raman spectra. We show that the size of Ni grains on Si substrates is correlated to the diameters of the grown carbon nanotubes.