Ha Jin Kim

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 500u200a°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.

Double-gated field emitter array with carbon nanotubes grown by chemical vapor deposition

We fabricated 4.75in. diagonal field emitter arrays with a double-gated structure in which the carbon nanotubes were synthesized by chemical vapor deposition using CO and H2 as feed gases. The nanotubes grown directly inside gate holes were used as an emitter. The diameter of the gate hole opening was as small as 4μm, accompanied with a large number of gate holes in a pixel. The electron beam spreading was minimized by employing a focus electrode. It was found that neither anode voltage nor focus electrode voltage had a strong influence on the anode current. The pixel-to-pixel uniformity of the fabricated structure was measured to be about 91%. Considering the limitation of the structure that has only a vertical resistive layer, it can be said that the fabricated field emitter shows quite a good uniformity.

Optimization of electron beam focusing for gated carbon nanotube field emitter arrays

We fabricated gated field emitter arrays with a novel focusing structure of electron beams, where the focusing electrode concentrically surrounded each gate hole. Carbon nanotube emitters were screen printed inside an amorphous-Si concave well far below the gate. It was theoretically and experimentally verified that the concave well structure effectively focused the emitted electron beams to their designated phosphor pixels by modulating focusing gate voltages. For the vacuum packaged field emission displays with the pixel specification fitting high-definition televisions, color reproducibility of approximately 71% was achieved at the brightness of 400 cd/m/sup 2/.

Effects of growth parameters on the selective area growth of carbon nanotubes

Abstract Effects of growth parameters such as plasma intensity, flow rate, composition of reactant gases, growth temperature, and hole size on the selective area growth (SAG) of carbon nanotubes (CNTs) were investigated using the triode type field emission array structure in plasma enhanced chemical vapor deposition (PECVD) system . As the plasma intensity was increased, the diameter of CNTs was reduced from 180 to 90 nm, but the growth rate was promoted. With an increase in the NH 3 flow rate, the average diameter of CNTs was decreased due to the enhanced etching effect by NH 3 . An increase in the total flow rate of reactant gases reduced the growth rate of CNTs, but the average diameter of CNTs remained nearly constant. An increase in growth rate and diameter was observed at higher growth temperatures. As the hole size of the triode structure increased, the growth rate of CNTs gradually decreased because of the reduced lateral diffusion of reactant species into the hole.

NH3 effect on the growth of carbon nanotubes on glass substrate in plasma enhanced chemical vapor deposition

Abstract The effects of NH 3 on the growth characteristics of carbon nanotubes (CNTs) were systematically investigated in plasma enhanced chemical vapor deposition (PECVD) with C 2 H 2 as a carbon source. CNTs were not formed when N 2 was used instead of NH 3 . Carbon films instead of CNTs were observed without NH 3 . As the growth of CNTs with only C 2 H 2 proceeded after the initial growth of CNTs with NH 3 and C 2 H 2 , films were formed with rugged surface morphology instead of nanotube-features. High-resolution transmission electron microscopy revealed that carbon films consisted of graphite carbons, and 20–30 nm graphite onions covered with amorphous layers. NH 3 was found to be essential to the growth of CNTs in the PECVD system. NH 3 may provide additional etching effects for the growing carbon surface, and suppression of carbon supply.

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

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 −200u2009V, 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...

Fabrication of field emission triode using carbon nanotubes

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.

Optochemically Responsive 2D Nanosheets of a 3D Metal–Organic Framework Material

Outstanding functional tunability underpinning metal-organic framework (MOF) confers a versatile platform to contrive next-generation chemical sensors, optoelectronics, energy harvesters, and converters. A rare exemplar of a porous 2D nanosheet material constructed from an extended 3D MOF structure is reported. A rapid supramolecular self-assembly methodology at ambient conditions to synthesize readily exfoliatable MOF nanosheets, functionalized in situ by adopting the guest@MOF (host) strategy, is developed. Nanoscale confinement of light-emitting molecules (as functional guest) inside the MOF pores generates unusual combination of optical, electronic, and chemical properties, arising from the strong host-guest coupling effects. Highly promising photonics-based chemical sensing opened up by the new guest@MOF composite systems is shown. By harnessing host-guest optochemical interactions of functionalized MOF nanosheets, detection of an extensive range of volatile organic compounds and small molecules important for many practical applications has been accomplished.

Growth of carbon nanotube field emitters on single strand carbon fiber: a linear electron source

The multi-stage effect has been revisited through growing carbon nanotube field emitters on single strand carbon fiber with a thickness of 11 µm. A prepared linear electron source exhibits a turn-on field as low as 0.4 V µm(-1) and an extremely high field enhancement factor of 19,300, when compared with those results from reference nanotube emitters grown on flat silicone wafer; 3.0 V µm(-1) and 2500, respectively. In addition, we introduce a novel method to grow nanotubes uniformly around the circumference of carbon fibers by using direct resistive heating on the continuously feeding carbon threads. These results open up not only a new path for synthesizing nanocomposites, but also offer an excellent linear electron source for special applications such as backlight units for liquid crystal displays and multi-array x-ray sources.

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

Vertically aligned multiwalled carbon nanotubes were synthesized by electron cyclotron resonance chemical vapor deposition on Ni-coated glass substrates at temperatures as low as 400u200a°C. Negative self-biases were induced to the substrates by radio frequency plasma to give ion bombardment to the growing surface. An increase of self-bias voltages from −50 to −200 V resulted in an evolution of the microstructures from amorphous carbon to nanorods, subsequently to nanotubes. Nanotubes grown above −150 V were more straight in morphology and better in crystallinity than nanorods grown at −100 V. In the field emission (FE) measurements, the electric fields to obtain 1 μA/cm2 were 4.6 and 11.1 V/μm for the nanorods and nanotubes grown at −100 and −200 V, respectively. The emission areas, calculated from the Fowler–Nordheim plots, were much larger in the nanorods than the nanotubes. It is considered that a larger amount of crystalline defects in nanorods plays a major role in improving their FE characteristics.