Kao-Chao Lin

Growth and field emission characteristics of carbon nanotubes using Co/Cr/Al multilayer catalyst

A multilayer catalyst, Co/Cr/Al, was employed to synthesize carbon nanotubes (CNTs) at atmospheric pressure by thermal chemical vapor deposition (thermal CVD). The relative growth rates, calculated on the basis of the average lengths of nanotubes grown at different temperatures, were utilized to estimate an activation energy of 0.84 eV for the multilayer catalyst. Such a low activation energy implies that the nucleation and growth of nanotubes could be effectively enhanced via the multilayer catalyst due to the well-distributed small catalytic nanoparticles by Al supporting layer and higher activity by Cr co-catalyst layer. It was also found that nanotubes grown using this configuration at 500 °C exhibited excellent field emission characteristics, and showed a highly uniform emission image in a phosphor-coated anode plate.

Carbon-Nanotube-Based Field Emission Devices with a Self-Focusing Gate Structure

Carbon nanotubes CNTs have attracted much attention for application in field emission displays FEDs due to their high geometric aspect ratios, chemical inertness, and excellent emission capacity. 1-3 Two types of operation configurations have been demonstrated in recent years: diode and triode. The triode-type configuration seems to be a promising candidate because of its better driving ability in low-voltage operation. 4-6 Several triode-type device structures have been proposed, including normal gate, under gate, and side gate structures, and the normal gate structure seems to be more promising in terms of low operation voltages as well as device performance. 7-11 For application to FEDs, a high anode voltage is essential for high efficiency of the phosphor, high brightness, and color purity. The high anode voltage requires a large vacuum gap between the cathode and anode plates so as to avoid the problem of arcing. Accordingly, the large vacuum gap may give rise to an issue of electron-beam spreading, which would cause cross talk between adjacent pixels and would deteriorate the resolution of displays. Therefore, a focusing structure which could effectively control the trajectory of electrons and reduce the cross-talk noise is necessary. Several focusing structures of FEDs have been announced to overcome the issue of electron-beam spreading, such as the planar electrode, 12 double-gate, 13 and mesh-electrode structures. 14 Those structures have some drawbacks, however, such as manufacturing complexity and reduction in emission current due to the focusing electrodes. In this work, CNT-based field emission devices with a selffocusing gate structure are proposed which do not require additional focusing electrodes as compared with other structures. The results of the simulation and luminescent images reveal good control of electron trajectory with this self-focusing structure, effectively reducing the spot size on the anode plate. Therefore, the focusing structure combined with simple processes is promising for application in FEDs.

Improvement of Luminescent Uniformity via Synthesizing the Carbon Nanotubes on a Fe?Ti Co-deposited Catalytic Layer

Uniformity has been considered to be one of the most important criteria for carbon nanotubes (CNTs) to be utilized as the emitters in field-emission displays (FEDs) or backlight units (BLUs). Using co-deposited Fe and Ti film as a catalyst, a uniform distribution of catalytic nanoparticles was obtained after hydrogen pretreatment as compared with nanoparticles obtained only using a pure Fe film. It might be attributed to the suppression of coalescence of the Fe nanoparticles in the co-deposited Fe–Ti film during the CNTs growth. In addition, the length variation of the CNTs synthesized by thermal-chemical vapor deposition (thermal-CVD) was also remarkably suppressed. This resulted in a significant improvement of the luminescent uniformity, and homogeneous light emission was obtained from the CNTs at 700 V.

Improved Field-Emission Properties of Carbon Nanotube Field-Emission Arrays by Controlled Density Growth of Carbon Nanotubes

The density distribution of CNTs is one of the crucial parameters determing the field-emission property of CNTs. To effectively control the density of CNTs, an inactive thin-film layer was deposited on a catalyst. The results showed that improved field emission property could be obtained with a thin SiO layer on the catalyst layer as the precursor. For 3.5 nm Fe and 3.5 nm SiO on 3.5 nm Fe as a catalyst, the turn-on field could be decreased from 3.7 V/µm. to 2.2 V/µm and the field-emission current density increased from 2.6×10-8 A/cm2 to 2.4×10-4 A/cm2 when the applied field was 4 V/µm

Properties of Carbon Nanotubes Via a Thin Ti Capping Layer on the Pretreated Catalyst

Screening effect and reliability are two of the most important issues in carbon nanotube-based field-emission devices. A thin Ti capping layer has been deposited on the hydrogen-pretreated catalytic iron nanoparticles to control the density of subsequently grown carbon nanotubes. In this way, the screening effect can be remarkably reduced due to the density of carbon nanotubes down to 10 7 from 10 9 cm -2 as compared to the control specimens. Thus, the turn-on field can be improved to be 2.1 from 3.8 V/μm at the emission current density of 10 μA/cm 2 . Furthermore, the electrical breakdown field can be increased to more than 7 V/μm and the lifetime of carbon nanotubes at high electric field (10 V/μm) can be greatly prolonged from a few seconds to more than 1 h. This can be attributed to better adhesion and lower contact resistance between the carbon nanotubes and the substrate.

The Reliability Improvements of Carbon Nanotubes Emitters by Utilizing an Fe–Ti Codeposited Catalyst

In this report, carbon nanotubes (CNTs) partially immersed into the codeposited metal layer have been synthesized by utilizing an Fe–Ti codeposited catalyst in a thermal-chemical vapor deposition system. This structure could enlarge the contact area between CNTs and substrates to provide better adhesion properties than that in the case of CNTs synthesized from a pure Fe film. Therefore, an abrupt decrease in emission current due to mechanical destruction at a high electric field and a gradual degradation in emission current due to Joule heating were remarkably suppressed. A stable emission current of about 30 mA/cm2 at 7.7 V/µm for 2,500 s was obtained without obvious degradation.

A Quasi-Planar Thin Film Field Emission Diode

A novel quasi-planar thin-film field emitter is fabricated by thin-film deposition and wet etching processes. The spacing between the emitters and collectors could be well controlled on the basis of the thicknesses of Cr thin films, which create submicron gaps. A forming process increases emitter surface roughness and results in a higher field enhancement factor, which shows better field emission characteristics. The turn-on voltage (at which the current level is 100 nA) of the device with a Cr thin film thickness of 300 nm is as low as 12 V, and the current fluctuation in 1 hour test at a driving voltage of 20 V represents a variation from -86 to +114%.

Field emission improvement through structure of intermixture of long and short carbon nanotubes

A novel density control with a structure of an intermixture of long and short carbon nanotubes (CNTs) is first obtained by precisely controlling pretreatment time and hydrogen content. This unique structure of CNTs is probably due to the uniform distribution of large and small iron nanoparticles under optimum pretreatment condition. Scanning electron microscopy is performed to confirm the morphology of catalytic nanoparticles after pretreatment. The obtained results show that a low turn-on field (~2.2 V/µm) and an ultra high field emission current density (0.4 A/cm2 at 6.46 V/µm) can be achieved through this novel structure of CNTs.

Growth and Field Emission Characteristics of Pillar-Like Carbon Nanotubes Using Co-Ti/Al Co-deposited Multilayer Catalyst at Low Temperature

In this essay, the pillar-like CNT field emission arrays synthesis with co-deposited catalysts at low temperature (550 ) was proposed. Pillar-like CNT has been successfully synthesized by thermal CVD system. The current density of this proposed pillar like CNTs was as high as 1272 2 -on field was 3.6 . Additionally, the reliability was more stable as lower than 7% degradation of initial current density.

7.2: Carbon Nanotubes Synthesized at Low Temperature and a Novel Self‐Focusing Gated Field Emission Device

A method for synthesis of CNTs at low temperature using thermal CVD is proposed. A multi-layered catalyst, Co/Ti/Al, has been successfully utilized to synthesize carbon nanotubes at 500°C by thermal CVD via modifying the flow rate of reaction gases. The flow rates of ethylene, hydrogen, and nitrogen are determined to be 125, 10, and 1000 sccm to improve the growth and field emission characteristics of CNTs at low temperature. Moreover, a novel self-focusing gated device was proposed to resolve the problem of electron beam divergence.