Effect of Vacuum on Carbon Nanotube Field Emission Display

Influence of Vacuum Degree on CNT Field Emission Display Tian Changhui12, Zhu Changchun2, Wang Qijun2, Liu Xinghui2, Wang Xiaoli2 (1. School of Science, Air Force Engineering University, Xi’an 7100512, China;School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China ) It is concluded that the electrons directly collide with the phosphor, and there is no gas discharge (plasma) causing the phosphor to luminesce. When the pressure is higher than 5 Pa, the voltage cannot be added due to the large amount of discharge gas (a certain short-circuit characteristic occurs between the anode and the cathode), and the screen cannot be observed to become bright. When the pressure is lower than 5Pa, in the pressure range of 5Pa to 01Pa, as the vacuum degree decreases (air pressure is large), the bright spot flickers to a large extent, and the indicator pointer of the pointer ammeter is significantly increased. Observed in the vacuum range of 0l1~10-4Pa, the change of air pressure has little effect on the field emission current and the brightness.

From the above observed facts, under the circumstance of carbon nanotube field emission, regardless of the gas pressure, the luminescence of the display is caused by electrons bombarding the phosphor. There is no problem that the electrons cause the gas discharge (plasma) to emit ultraviolet light to cause the phosphor to emit light. When the vacuum is low, the gas ionization will reduce the voltage actually applied between the cathode and the anode, so that electrons cannot be emitted.

Fund Project: National Natural Science Foundation of China Key Program (60036010) Ministry of Education Doctoral Fund Project (2000069823) Claw: c Tianchang Shaanxi Shipwright Granted the CNT to shoot the monitor. Theoretical analysis Since the electronic work function of gas molecules is much larger than that of carbon nanotubes, the probability of gas molecules directly relying on the electric field to ionize is small. The effect of vacuum degree on the emission of carbon nanotubes should be mainly Caused by electronic collisions. These collisions have the following effects: changing the direction of electron motion, reducing the directional energy of the electrons, ionizing the gas, or causing the gas to emit ultraviolet light, which then causes the phosphor to emit light. The impact of vacuum on field emission is analyzed by calculating the collision frequency of electrons and gas molecules.

21 Electron Collision Frequency Calculation During the process of electrons moving from the cathode to the anode, it is theoretically analyzed that electrons and electrons and electrons and gas molecules should collide.

Since the electron radius is much smaller than that of gas molecules, and the electron motion is mainly acceleration motion in the same direction, the collision probability between electrons is completely negligible with respect to the collision of electrons with gas molecules. According to the theory of gas molecular dynamics 13|, electrons are considered as another gas (ie, a model that considers two kinds of molecular collisions), and taking into account that the electron radius is much smaller than that of gas molecules, and the electron speed is much greater than that of gas molecules. The average free path of an electron motion can be derived: The average collision frequency of electrons and gas molecules is based on, the current density is related to the distance between cathodes and anodes, and has nothing to do with the electron velocity. Based on this calculation and taking into account that the number of electron bombardment phosphors is also proportional to the current density, so I think that measuring the effect of vacuum on the display uses a product of air pressure and anode and cathode spacing (pd) more reasonable than using air pressure (p). The greater the gap between cathode and anode, the higher the vacuum required by the device. The ignition voltage of the gas in the tube plate display (P§P) is gds. The balance between the frequency of the electron collision and the gas pressure is calculated using the parameters in Table 1 for normal displays.

The relationship between electron mean free path and gas pressure The collision frequency and pressure of electron and gas are shown in Table 1. The electron current density calculation and analysis circuit shows that the current in the circuit is generated by the electron motion, and the middle unit moves from the cathode to the anode. The total number of electrons should be equal to the indicated value of the ammeter in the loop divided by the charge of the electron. According to the definition of current density, calculate the current density of the test J = IAS -2 This value is basically consistent with the relevant research report 151. According to the relationship between the current density J and electron density electron charge e and electron velocity Ve: can be obtained The number of electrons per unit time from the cathode to the anode per unit area can be seen. Under the 200mm cathode and anode spacing, the collision frequency of electrons and gas molecules per unit area is 1017~1018m-2s-1 at 5Pa atmospheric pressure. It can be seen that this value is close to the number of electrons per unit time from the cathode to the anode, which indicates that a large number of electrons collide with the gas to ionize the gas, reducing the electric field strength between the cathode and the anode, and the electrons cannot be emitted.

3 Conclusions Through experimental observation, it can be shown that, under the circumstance of carbon nanotube field emission, regardless of the gas pressure, the luminescence of the display is caused by the electron bombardment of the phosphor, and no electrons cause the plasma luminescence to cause the phosphor to luminesce. When the vacuum degree is too low, the gas ionization will cause short-circuit characteristics between the anode and the cathode, which will reduce the voltage actually applied between the anode and the cathode, so that electrons cannot be emitted.

The calculation of the collision probability between electrons and gas molecules shows that using the product of the gas pressure and the distance between cathodes and anodes as a standard, it is more reasonable to measure the effect of gas on the field emission than just using vacuum. The larger the cathode and anode spacing of the field emission display, the higher the vacuum requirement.

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