Emission and life characteristics of thin film top-layer scandate cathode and diffusion of Sc O and W

We investigated top-layer scandate cathodes, which are the most promising of scandate cathodes. Among the cathodes which we prepared with a layer of various thickness, the best pulse emission of 80 Arcm2 at 1300 K was recorded with cathodes having a top layer consisting of a Sc2O3 layer 2 nm thick on a W layer 8 nm thick. The emission variation of these cathodes was evaluated in life tests. The life characteristics were good in both diode and triode evaluation. We also determined diffusion coefficients of W and Sc2O3 with unporous W pellets covered with a Sc2O3 and W layer. Variations of surface concentrations of these pellets during life tests were measured using Auger electron spectroscopy. The diffusion coefficients were 6.4=10y19, 1.0=10y18, and 1.6=10y18 cm2rs at 1220 K, 1300 K, and 1370 K. Chemical states of O, Sc, and W are discussed based on detailed analysis of Auger electron spectra. q1999 Elsevier Science B.V. All rights reserved.