Chuan-Ping Juan

Effects of High-Density Oxygen Plasma Posttreatment on Field Emission Properties of Carbon Nanotube Field-Emission Displays

The effects of oxygen plasma posttreatment (PPT) on the morphology and field emission properties of carbon nanotube (CNT) arrays grown on silicon substrates are proposed and experimental results are reported. Oxygen PPT led to an enhancement in the emission properties of CNTs, which showed an increase in total emission current density and a decrease in turn-on field after plasma treatment. Scanning electron microscopy (SEM) images showed reduced densities of the CNTs, which resulted in a decrease of the screening effect in the electric field. Raman spectra showed an increase in the number of defects which served as field-emission sites when the plasma power or treatment time with the plasma increased. Transmission electron microscopy (TEM) images were used to identify the quality of the nanotubes, so that we could clearly find evidences of improvement in the field emission properties after plasma treatment. The measurement of electrical characteristics revealed improved field emission properties under proper plasma conditions. The turn-on field decreased from 4.8 to 2.5 V/µm, and the emission current density increased from 78.7 µA/cm2 to 18 mA/cm2 at an applied field of 5.5 V/µm.

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.

Pillar Height Dependence of Field-Emission Properties in an Array of Carbon Nanotube Pillars

Carbon nanotube pillars with optimal field-emission properties, including a high field enhancement factor β of 5384 and a low turn-on field Eto of 0.84 V/µm, have been achieved when the ratio of interpillar spacing to pillar height is 2. However, when this ratio exceeds 2, the field enhancement factor increases with increasing pillar height since the field can be enhanced by increasing the aspect ratio. When the ratio is smaller than 2, the field enhancement factor decreases with increasing pillar height owing to the increased field-screening effect. A simulation has been performed to verify the experimental results.

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.

Fabrication and Characterization of lateral Field Emission Device Based on Carbon Nanotubes

A lateral field emission device based on carbon nanotubes (CNTs) is proposed and the experimental results are reported. In this method, the distance between polysilicon anode and the CNTs cathode was determined by the wet etching process. Thus, the interelectrode gap is easily formed in good uniformity and reproducibility with dimensions below 1 micrometer. The CNTs were selectively grown with microwave plasma enhanced chemical vapor deposition system (MPCVD). The turn-on voltage of the fabricated device with interelectrode gap of 0.6 /spl mu/m is as low as 2 volt, and the emission current density is as high as 4 mA/cm at 20 volt. The emission current fluctuation is about /spl plusmn/15% for 2100 sec.

Dependence of Ferroelectric Characteristics on the Deposition Temperature of (Pb,Sr)TiO3 Films

The pulsed laser deposition (PLD) of (Pb,Sr)TiO3 (PSrT) films on Pt/SiO2/Si at low substrate temperatures (Ts), ranging from 300 to 450 °C, has been investigated. The PLD PSrT films prepared at low Ts exhibit ferroelectric properties, good crystallinity, and no significant interdiffusion between the PSrT film and the Pt bottom electrode. The conduction mechanism is identified as Schottky emission at low electric fields and as Poole–Frenkel emission at high electric fields. PSrT films grown at appropriate Ts yield fewer interface states and fewer trapping states, leading to a smaller leakage current. The enhanced (100) preferred orientation of PSrT films deposited at Ts=350–400 °C exhibits optimum ferroelectricity. In addition, the dielectric constant and ferroelectricity are associated with the preferred orientation. This shows that the electrical characteristics strongly rely on the preferred orientation and trapping states, which could be controlled by varying the substrate temperature (Ts≤450 °C) during PLD.

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.

Coaxial-Structured Solar Cells with Silicon Nanostructures

Coaxial-structured solar cells with different lengths silicon nanowires (SiNWs) fabricated by e-beam lithography and transformer coupled plasma reactive ion etching (TCP-RIE) were demonstrated in this paper. With the intrinsic amorphous silicon thickness of 15 nm and n-layer thickness of 25 nm, the shortcurrent density and the conversion efficiency of the flat film solar cell were 17.58 mA/cm and 3.16 %, respectively. Furthermore, the short-current density increased from 20.75 to 27.90 mA/cm and the conversion efficiency increased from 3.59 to 4.69 % when the silicon nanowires length was increased from 0.5 to 1 μm. The proposed coaxial-structured solar cells with SiNWs exhibited nearly 48.42 % efficiency enhancement over the plat film solar cell.