The carbon nanotube has good field emission properties, so it has been used as the electron source on the field emission display panel. To obtain a high emission current, the electric field at the tip of the nanotube must be large enough. This article studies the variation of electric field with different types of nanotubes. The emission current of the nanotube is also calculated for various geometrical parameters of nanotubes. From the simulation results, the influence of the geometrical parameters on the emission performance of nanotubes is studied.

In the normal gate CNT-FED, the gate electrode is used to modulate and address the electron beam. Some electrons may bombard on the gate electrode, thus the luminant efficiency of CNT-FED decreases. This paper proposes a new gate structure, which is the metal mesh with cone funnels. MgO film and MgF2 film are vaporized on the surface of the mesh and the funnels. When the primary electrons bombard on the gate electrode with initial energy, the secondary electrons and backscatters are generated. As results, more electrons can pass through the gate electrode and land on the anode. Consequently, the brightness of the novel triode structure CNT-FED can increase obviously. In the paper, we show the results of numerical simulation of the secondary electron emission process with Monte Carlo method. Some CNT-FED devices with the new type of gate structure are fabricated. The surface of the gate electrode is coated with MgO, MgF2 and SiO2 film, respectively. The results of emission experiments are also shown in this paper.

Charge accumulations on the wall of the chunnels in field emission devices are analyzed with the Monte Carlo method. The chunnel's wall is dielectric, and secondary electrons are generated when electrons hit the chunnel's wall. Under the electron bombardment, the secondary emission induces charging on the wall. It is implied that in the field emission process, the upper part of the chunnel's inside wall is positively charged, while the lower part of the chunnel's inside wall and the chunnel's underside wall are negatively charged. Four models with different forms of chunnels are studied. We analyze the effect of charge accumulation in different models by comparing the potential distributions near the cathode and the current density distributions of the cathode, respectively. The results show that increasing the slope of the chunnels will reduce charge accumulations at the chunnel's underside wall. Also, the energy distributions of electrons arriving at the anode are analyzed, and it suggests that the chunnel's slope may decrease the ratio of primary electrons directly on the anode to all the electrons on the anode.

In the manufacture of electron optical system, the dimension and alignments of the electrodes may have some small perturbations. The performance of the electron optical system is affected by these tolerances. It is important to analyse the in#uence of the tolerance. Usually, the perturbations of the potential and the trajectory are obtained by the difference of parameters at various positions of the movable electrode. Because the value of the tolerance is usually very small, it is diffcult to estimate the acceptable tolerance. Serious numerical error may also be introduced in this method. This paper proposes another method to determine the acceptable tolerance in the manufacture. In this method, the derivative of the potential versus the displacement vector is obtained from the unperturbed field. Then the derivative of trajectory is calculated with the RK method from the normal result. According to the first-order approximation, the acceptable tolerance can be determined. This paper analyses some typical perturbations in the main lens of CRT. (1999 Elsevier Science B.V. All rights reserved.

The fabrication of carbon nanotube emitters with excellent emission properties is described. The multi-walled carbon nanotubes (MWNTs) produced by chemical vapor deposition (CVD) method were purified with oxidation method and mixed with organic binding pastes and then screen-printed on glass substrates with ITO film. We applied anode voltage gradually to refine the emission behavior of the emitter by cleaning the top surface of screen-printed carbon nanotubes (CNTs). The density of the carbon nanotubes is about 2:5 108/cm2. Diode field emission experiments were performed in dynamic vacuum system to study the emission current, the emission uniformity, etc. Bright and stable character emission images were obtained in the diode structure and the emission current could approach 1 mA/cm2.

In the design of a charged particle optical system, many geometrical and electric parameters have to be optimized to improve the performance characteristics. In every optimization cycle, the electromagnetic field and particle trajectories have to be calculated. Therefore, the optimization of a charged particle optical system is limited by the computer resources seriously. Apart from this, numerical errors of calculation may also influence the convergence of merit function. This article studies how to improve the optimization of charged particle optical systems. A new method is used to determine the gradient matrix. With this method, the accuracy of the Jacobian matrix can be improved. In this paper, the charged particle optical system is optimized with a Message Passing Interface (MPI). The electromagnetic field, particle trajectories and gradients of optimization variables are calculated on networks of workstations. Therefore, the speed of optimization has been increased largely. It is possible to design a complicated charged particle optical system with optimum quality on a MPI environment. Finally, an electron gun for a cathode ray tube has been optimized on a MPI environment to verify the method proposed in this paper.