The Preparation And Mechanism Of Anti-electron Emission Hf And SiC Thin Film

In this dissertation, the effect that hafnium film has on the suppressing grid emission in pulsed-controlled grid traveling wave tubes has been studied, while the working mechanism of Hf films has been discussed. In our experiments, the hafnium films were deposited on molybdenum substrates by radio frequency magnetron sputtering technology, and the barium oxide layers were prepared by the chemical method to simulate the grid structure of traveling wave tubes. Then, the surface phase and compositional change in the grid was studied under high temperature by annealing from 900K to BOOK, which can be used in explaining the suppression mechanism of hafnium film.The electron-emission characteristics of the grids with and without Hf, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using an analogous-diode method. The surfaces of the grids were analyzed by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The results showed that electron-emission current from the Mo grid coated with Hf film was less than that from the Mo grid without Hf. During the course of the testing, active electron-emission substances from the cathode were deposited continuously onto the surface of the grid. Due to BaHfO₃ and Ba₂HfO₄ compounds and Ba-Hf diffusion, the Mo grid coated with Hf effectively reduced the electron-emission substances on the grid from the cathode, which reduced grid electron emission.On the other hand, we studied some character of SiC films. We have studied that in different conditions, the SiC films performed different character such as FT-IR., XRD and so on.