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Tetrapod zinc oxide (T-ZnO), being a kind of nano-material, has large specific surface area and surface binding energy, which will make it sensitive to the ambient gas condition. So the field emission properties will be influenced by the gas adsorption when being applied as the cathode materials of field emission devices. Carbon monoxide is the main residual gas in T-ZnO field emission devices. In this paper, carbon monoxide was introduced into a field emission device with T-ZnO emitters. The field emission currents of tetrapod ZnO were compared before and after exposure to CO.

To study the mechanism of current degradation of a cold cathode, the outgassing measurement of a field emission diode with tetrapod zinc oxide (ZnO) cathode has been taken with a quadrupole mass spectrometer (QMS) in an ultra-high vacuum (UHV) system. It was found that the H2, CO2, CO, and CH4 were outgassed from the diode during the working process. The partial pressure of outgassing increases with the increased emission current density. The field emission properties of the cold cathode, such as turn-on field, threshold field and the emission current density, were largely related to the pressure of the outgases. From the outgassing experimental results, the relation between the emission current degradation and the outgassing of field emission devices has been found. Due to the outgassing, the work function of ZnO cold cathode increases, while the field enhancement factor decreases. Therefore, the outgassing plays very important role in the current degradation for the field emission devices (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Zinc oxide is a wide band gap semiconductor (WBGS). Its band bending, which usually favors field emission by lowering surface barrier and bringing more electrons to the bottom of conduction band, can be quite dramatic under high field. In the last few years, different kinds of ZnO nano-materials has been synthesized and applied as the cathode materials for field emission. For better application of ZnO in commercial field emission devices, long-term current stability is one of the most important aspects to be ensured. So in this paper, the field emission behavior of screen printing tetrapod ZnO will be studied by exposing to CO, which is the main residual gas in sealed tetrapod ZnO (T-ZnO) field emission device.

In order to study whether the ambient gases affect the emission current stability of the cathode, the cathode should be the same one. In addition, the working condition should be kept constant except the ambient gas condition, so that other factors, which may also lead to the emission current degradation of the cathode, can be avoided. Only the influence from the residual gases will be concerned. For this consideration, an experimental system was set up, as shown in Fig. 1. It consisted of a vacuum system with a quadrupole mass spectrometer (QMS) and FE device opening set to introduce the residual gases inside the FE device into the analysis system.

The effects of ion bombardment on the field emission of screen printed tetrapod zinc oxide cathodes are reported. The field emission characteristics of this cathode degrade strongly after Ar ion bombardment for 10min at an energy of 3keV and ion current of 5µA. The emission current density decreases from 1.65 to 0.32mA/cm2 at 4.50V/µm field strength, while the turn-on field increases from 2.16 to 3.11V/µm at a current density of 0.1µA/cm2. This result demonstrates that the field emission of the ZnO emitters severely degrades upon ion bombardment. The emission degradation can be attributed to a lower value of the field enhancement factor β, which is caused by changes of the morphology, and a higher work function ϕ, which is caused by changes of the surface composition of ZnO.

Tetrapod zinc oxide (T-ZnO), being a kind of nano-scale material, has a large specific surface area and high surface binding energy, which will make it sensitive to ambient gases; hence, the field emission (FE) properties of this ZnO nanomaterial will be influenced by gas adsorption. The effect of methane on the field emission of T-ZnO emitters was investigated. It was found that CH 4 enhanced the field emission substantially. By curve fitting we are able to describe the experimental results adequately as a function of the methane pressure. The increase of the field emission is caused by a lower work function of the ZnO-emitters.

The Ba and BaO evaporation rates of a thermionic cathode have been measured at 145K and 170K above the typical operating temperature being about 1033K. According to the measurement result, the relationship between cathode lifetime and operation temperature has been discussed. A comparison life test also be done between a poisoned but reactivated cathode and a normal one under the same condition. We found almost the same emission current at the beginning but different current decrease speed and Ba evaporation rate at the course of the life test.

Evaporation of carbon nanotubes (CNT) cathodes and the degradation of its field emission are reported in this paper. After 100h at 1323K the emission current density decreases from 6.50 to 0.20mA/cm2 at 7.50V/µm field strength, while the turn-on field increases from 1.92 to 2.45V/µm at a current density of 0.1µ/cm2. The C+-ion current in a mass spectrometer has also been measured to compare the CNT evaporation at different cathode temperatures between 1173K and1373K. The results indicate that the CNT evaporation rate increases greatly at temperatures above 1100K. Scanning electron microscopy (SEM) images show that the emission degradation can be mainly attributed to the decreased value of field enhancement factor β, which is caused by CNT evaporation.

The true outgassing from cathodes is often masked by the production of gases released by phosphors in field emission displays (FEDs). The outgassing characteristics of CNT cathode and ZnO cathode for application in FEDs are presented. Quadropole mass spectrometer[QMS] has been used to measure the outgassing characteristics from carefully prepared samples of CNT and ZnO cathodes in ultra-high vacuum(UHV) system. We observe that the outgassing rate of Z n O cathode is much lower than it of CNT cathode due to its solid structure, but they have the similar outgassing. It has been shown that the main components of released gases are water vapor, carbon monoxide, carbon dioxide and oxygen.

Field emission characteristic and stability of a carbon nanotubes (CNTs) cathode have been studied by testing the emission current at different levels. By monitoring the emission I-V curves, we can obtain a relative stable maximum current from a CNTs cathode, after reaching the maximum current, the emission current fluctuate seriously and sparking can be seen at the site of emission. From the experimental results, the causes of emission instability and sparking is concluded and the influence of the sparking and ion bombardment on the emission performance of a CNTs cathode is obtained

In this paper, a novel gun of RF power amplifier based on always-on cathode was described. Double hopping electron funnels are fabricated into the devices. RF modulated signal is applied on the aluminum electrode. The process of secondary electron emission, potential distribution and trajectories were simulated. In the simulation model, the primary electrons, which are low energy, emit from the ring cathode with proportional spacing

An efficient method is used to improve the emission stability and uniformity of the field emission from a carbon nanotube (CNT) cathode. In this method, a fully sealed device with CNTs cathode is exhausted by a pumping system. At the same time, this device is baking at a temperature about 400degC and maintains for a few minutes, and an overload current is applied. The overload current can burn the nanotubes which are over-outcrop to the surface. Besides this, successive emission cycles process is designed to aging the cathode and get rid of the residual gas stored in the cathode layer. Consequently, the emission stability and uniformity of a CNTs cathode have been improved apparently

A new triode structure for printable carbon nanotube field emission displays is described in this paper. In the structure, silver paste is printed on the surface of a metal mesh and acts as the gate electrode. Between the gate and the metal mesh is a dielectric layer. MgO film and MgF/sub 2/ film are deposited on the surfaces of the mesh and the funnels by evaporation. A voltage applied on the metal mesh, the primary electrons emit from the CNT cathode and bombard on the surface of the metal mesh with initial energy. The secondary electrons and backscatters are generated. Because of the low energy of the secondary electrons, the gate can control the emission current easily. Therefore the range of the modulate voltage can be withdrawn. The dielectric layer on the surface of the metal mesh must be compact, otherwise silver paste will penetrate in after firing and under high voltage, breakdown of the insulator materials will occur by surface flashover. This paper reports the fabrication process of dielectric layer and the preparation of the materials.