Study on the composition and phase change of BaO/Hf/Mo under high temperature

Hafnium films were deposited onto the molybdenum grids by radio-frequency magnetron sputtering from an Hf target in argon gas. Emission current of Mo grids coated with and without Hf film during the lifetime testing, which were contaminated by active electron-emission substances (i.e. Ba or BaO) from the cathode, were measured using an analogous-diode method. The results show that emission current from the Mo grid coated with Hf film is much less than that from the Mo grid without Hf film. The BaO layer was deposited on Hf/Mo substrates by chemical method in order to simulate the working conditions of the grids contaminated by electron-emission substances from the cathode. The suppression mechanism of electron emission from the Mo grid coated with Hf film is discussed according to the experimental results and the calculation of the reaction free energy.