Hf was deposited onto the surface of Mo grids by ion-beam-assisted deposition. 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 and x-ray photoelectron spectroscopy. The results showed that electron-emission current from the Mo grid coated with Hf film was less than that from the Mo grid without HE 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 compounds and Ba-Hf diffusion, the Mo grid coated with Hf effectively reduced the electron-emissiori substances on the grid from the cathode, which reduced grid electron emission. © 2005 American Vacuum Society.