Jinchan Wang

Effect of ion bombardment on the field emission property of tetrapod ZnO

The influences of ion bombardment on the field emission performance of tetrapod ZnO nanostructures are reported. As the scanning electron microscopy images and photoluminescence spectrum show, the tips of the field emitters are destroyed and the surface state of the field emitters is also changed after the ion bombardment. The ion bombardment has a considerable effect on the field emission properties of the tetrapod ZnO field emitters. After Ar+ ion bombardment with the energy of 3 keV and the ion current of 0.05 μA for 30 min, the turn-on field increases about 63% and the threshold field increases about 77%, respectively. There are two main reasons for the variation in field-emission property: (1) the decrement of the field enhancement factor β, which is caused by the variation in morphology of field emitter; (2) the increment of work function φ, which is caused by the changed concentration of the surface oxygen vacancy.

Study of a micro chamber quadrupole mass spectrometer

Copyright @ 2008 American Vacuum Society / American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Vacuum Science and Technology Part A: International Journal Devoted to Vacuum, Surfaces, and Films, 26(2), Article number 239 and may be found at http://scitation.aip.org/content/avs/journal/jvsta/26/2/10.1116/1.2827512.

Residual gas analysis based on carbon nanotube field emission display

The authors measured the residual gas spectrum of a field emission display (FED) with carbon nanotube (CNT) emitters and found that the main residual gases inside a sealed CNT FED, containing an evaporated Ba getter, are H2, CH4, CO, Ar, and CO2, all of which are typical residual gases of electronic vacuum tubes. Additionally they also measured the electron stimulated desorption of gases by operating their field emission devices.

Novel gun of rf power amplifier based on always-on cold cathode

A novel gun double hop gun of rf power amplifier based on an always-on ringed cold cathode is suggested. Double hopping electron funnels, including a metal funnel and a glass funnel, are fabricated in. MgO film is deposited around the walls of the funnels by electron beam evaporation. Secondary electrons or backscatters (elastic and inelastic) escape from the dielectric film (MgO) under the bombardment of accelerated electrons and are driven to the exit window of the glass funnel by a modulated voltage. Among the escaping electrons, the ratios of secondary emission electrons, elastic scatters, and inelastic scatters are 90%, 9%, and 1%, respectively. Most of the escaping electrons at the exit window have low energy (<50eV) and can be easily controlled by the modulated voltage with low amplitude (∼100V) applied on the electrode of the glass funnel. The average velocity in the Z direction of the escaping electrons increases as the amplitude of the modulated voltage (Vgate) increases. The distributions of th...

Effect of CO on the field emission properties of zinc oxide

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.

Study the electronic responses of individual nanoparticles by electron energy loss spectroscopy in a transmission electron microscope

Plasmon coupling of dimers of Ag nanoparticles is studied by the EELS as shown in Fig 1a [1]. The spectroscopic images in the above Fig. 1a are extracted from 2.8eV, 3.4eV and 3.6eV respectively, where one can see the preferable exciting points of the features around the Ag nanoparticles. With the aid of DDA calculation(Fig. 1b), the three features are identified as the in-phase plasmon coupling, non-coupling and anti-phase coupling modes. The in-phase mode is able to conduct the light transportation due to its dipolar nature, which redshifts from the 3.4eV at large spacings to 2.7eV near touching (Fig. 1c). Such behaviour is also observed in the chain of 3 and 4 nanoparticles. The experiment provides clear evidence on the plasmon coupling of Ag nanoparticles. Extracting the dopant states in the Co-doped ZnO nanoparticles [2]. In order to assign the dopant-introduced states in the low-loss EELS, we employ both the core-loss EELS and the valence EELS on the same Co-doped ZnO nanoparticles by spatially mapping the dopant concentration distribution via the core-loss EELS (Fig 2a 2b 2c) and simultaneously by identifying the dopant features in the accumulated valence EELS via the measured dopant richness (Fig 2d). Three Coincidentally-growing Co dopant states are successfully determined in Fig. 2e. The experimental inputs feed the first-principles calculation, which generates full electronic structure of the doped ZnO nanoparticles. The experiment supports the carrier mediated room-temperature magnetism, which is a main confusion with current dilute magnetic semiconductors.

Ambient gas properties of field emission devices

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.

Effect of ion bombardment on the field emission of a zinc oxide cathode

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.

Ba/BaO evaporation measurement during accelerated life test

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.

Enhanced field emission of tetrapod zinc oxide in methane

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 CH4 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.