Jae Eun Jung

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.

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.

Carbon nanotube field emitter arrays having an electron beam focusing structure

An electron beam focusing structure was incorporated into the gated field emitter arrays where the emitters were screen-printed carbon nanotubes. The focusing structure was comprised of 8-μm-thick bulky SiOx focus gate insulator and Cr focus gate, and exhibited negligible leakage between the gate and the focus gate. In current–voltage measurements, it is found that the anode current strongly depends on both the focus gate and the anode bias voltages. Electron beams were focused well at the anode with a slight overfocusing effect, which is due to the wide electron beam divergence from carbon nanotubes. A new focusing structure based on the simulation is proposed to overcome the overfocusing.

Carbon Nanotube-Based Field-Emission Displays for Large-Area and Full-Color Applications.

Single-wall carbon nanotubes (SWNTs) were applied to electron emitters of field-emission displays (FEDs). Large-area FED devices with SWNT emitters were successfully fabricated in a diode mode using screen printing 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 FED structures to achieve a high gray scale and high brightness. It was observed that electron emission from carbon nanotube emitters was controlled by the modulation of gate voltages.

Investigation of nonionic diazo dye-doped polymer dispersed liquid crystal film

Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV–Vis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (V

A Nanogripper Employing Aligned Multiwall Carbon Nanotubes

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Structural Characteristics of Carbon Nanorods and Nanotubes Grown Using Electron Cyclotron Resonance Chemical Vapor Deposition

, increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.

Fabrication of field emission triode using carbon nanotubes

Nanogripper structures using aligned multiwall carbon nanotubes (MWCNTs) are demonstrated and their electromechanical properties have been studied in this paper. The balance of electrostatic force, together with elastostatic force and van der Waals force determines the driving conditions. A triode structure drastically reduces the bias between two moving parts, which consist of MWCNTs. Low bias also enables low power consumption as well as the reduction of electrical damage to an object. The moving parts can keep the same state without any applied biases after bending and connection. This also enables power saving during driving. The device can be a base structure for various nanorobotic or other nanoelectromechanical devices.

Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles

Different types of carbonaceous materials were synthesized by electron cyclotron resonance chemical vapor deposition on Ni-coated glass substrates with radio-frequency (rf) self-biasing using a gas mixture of CH4 and Ar. Vertically aligned carbon nanorods and multiwalled carbon nanotubes (MWNTs) were obtained at the rf bias voltages of −100 and −200 V, respectively. High-resolution transmission electron microscopy indicated that the distance between two graphene layers of carbon nanorods is much larger than that of well-graphitized MWNTs having a typical value of graphite. Structural characteristics of carbon nanorods and well-graphitized MWNTs were investigated by electron-energy-loss spectra, in which the energy of π+σ plasmon peak obtained from carbon nanorods shifts to a lower value of 23.8 eV, compared to 25.5 eV from well-graphitized MWNT. Low-energy loss plasmon due to π electrons at 6 eV was not observed in carbon nanorods, but clearly defined for well-graphitized MWNTs. In addition, x-ray photoel...

Field emission characteristics of multiwalled carbon nanotubes grown at low temperatures using electron cyclotron resonance chemical vapor deposition

Abstract We have fabricated the triode for field emission display on soda-lime glass using carbon nanotube as an emission tip. Selective growth of carbon nanotubes was carried out on the emitter hole with the size of 1.2 μm in diameter using plasma enhanced hot filament chemical vapor deposition (HFPECVD). The emission characteristics of the fabricated triode showed that turn on electric field was 7 V/μm in diode mode and that on–off control of the emission current was achieved by gate voltage of 1 V. The emission current increased from 3 to 28.5 μA as the gate voltage increased from 0 to 2 V at the anode voltage of 1900 V.