Robert Baptist proposed in 1996 field emitter arrays (FEAs) with microtip cathodes as electron sources in vacuum sensors. Since then a decade has passed without commercial use in total pressure measurement applications. The use of FEAs in XHV partial or total pressure measurement also did not pass the laboratory stage. The reasons are costly manufacturing in comparison to thermionic cathodes and the susceptibility of microtip cathodes to degradation at higher pressures.
Today, electron sources based on carbon nanotube (CNT) field emitters are a true alternative to FEAs with microtip cathodes. CNTs with a diameter below 20 nm possess the best field emission properties and are very robust mechanically, which justifies their use in field emission cathodes for vacuum sensors.
Starting from basic research to characterize field emission properties, long term stability and stress of CNT field emitters [2,3], we present investigations of CNT field emitter electron sources of different provenance in an ionization gauge. We used emission currents of 1 mA and an upper pressure limit of 1 Pa. We compare the results with those of Dong [4] and discuss advantages to a Bayard-Alpert gauge with thermionic cathodes. Focus of the presentation is the dimensioning of the CNT cathode for applications in ionization gauges.
[1] R. Baptist et al., J. Vac. Sci. Techn. B, 14 (1996) 2119-2125.
[2] W. Knapp, D. Schleussner, J. Vac. Sci. Technol. B, 21, 1 (2003), S. 557- 561.
[3] W. Knapp,D. Schleussner, Appl. Surf. Science 251 (2005) 164-169.
[4] C. Dong et al., Applied Physics Letters 84 (2004) 5443-5445.
|