Study On Thermionic Emission Mechanism And Surface Analysis Of La-Mo Film Cathode Deposited By Pulsed Laser Deposition

La₂O₃-Mo cathode used for the vacuum emission tube is a new kind of emission materials which have being hoped to replace radioactive ThO₂-W cathodes. Cathode emission is a kind of superficial phenomenon. Cathode emission performance depends principally on the cathode materials'composition and configuration of the surface layer. Experiments have verified the formation of LaOx (x<1.5) which plays an important role in the La₂O₃-Mo cathode emission. How the surface La/O ratio to influence cathode property is difficult in getting proof because cathode work under the high vacuum environment as well as Lanthanum is easy to oxidize since cathode is discovered 40 years ago. Investigating thoroughly the function of surface layer in the electron emission will be benefit to the understanding of cathodes mechanism and provide the theory guiding for the extensive application. This thesis investigates firstly the task using a new device which is acquired by reforming the vacuum chamber of AES (Auger energy spectra) and connecting with PLD (pulsed laser deposition). By means of PLD we prepare different La/O ratio thin film to simulate cathode surface active layer, test the emission properties and analyses surface composition in similar work environment. The relationship between cathode surface La/O ratio and cathode emission performance is firstly determined. The paper gave the theoretical analysis about cathode working mechanism at the different stages when cathode surface La/O is changing and put forward the new cathode emission theoretical viewpoint which is different from that of traditional theory and explained the actual experiment phenomenon. The thesis confirmed the best deposition craft by means of understanding the function of each part of the cathode device. The final craft as follow: deposition time 15 minutes, thin film thickness 100nm, test temperature 1483K. LaO_x (x<1.5) films were prepared by pulsed laser deposition (PLD) under various vacuum conditions. By controlling the ambient pressure, nonstoichiometric La-rich La–O films were gained. The electron emission properties of these cathodes were measured in the film deposition chamber without exposed to the atmosphere.