IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Vacuum Science & Technology Monday Sessions
       Session VST-MoM

Paper VST-MoM2
Getter Requirements for a CRT with a Diamond Coated FE Electron Source

Monday, October 29, 2001, 10:00 am, Room 125

Session: Sealed and Insulating Vacuum Systems
Presenter: V. Nemanic, ITPO, Institute of Surface Engineering and Optoelectronics, Slovenia
Authors: V. Nemanic, ITPO, Institute of Surface Engineering and Optoelectronics, Slovenia
M. Zumer, ITPO, Institute of Surface Engineering and Optoelectronics, Slovenia
B. Zajec, ITPO, Institute of Surface Engineering and Optoelectronics, Slovenia
T. Tyler, North Carolina State University
Correspondent: Click to Email
A single diamond coated field emitter (FE) tip could be used as a replacement for the thermionic cathode in small electron beam devices offering better opto-electronic performance. The most important parameter limiting the use of field emitting sources is their short lifetime, which is closely related to the pressure level within the pinched off device. After the initial evacuation of the tube and bake-out, getter selection and the activation procedure would seem to play the crucial role. In the present study, the pressure of miniature CRTs was measured by a spinning rotor gauge (SRG) after the initial evacuation and bake-out procedures, again after activation of the getters, and finally during operation under typical operating conditions. Two commercial getter types were studied: Ba evaporable (St15/AM/O/9.5) and non-evaporable (NEG, St 172), made by SAES and built into the CRTs with either an oxide coated thermionic cathode or a diamond coated FE tip. The later were fabricated by electrochemically etching 125µm molybdenum wire in KOH, resulting in tips with radii of @<=@ 50nm. The bare tips were then coated with nanodiamond via electrophoresis using a 2g /L suspension of diamond in ethanol. After the evaporation of barium getters by the prescribed procedures, the pressure did not drop, but increased slowly from 1x10@super - 5@ mbar up to 1x10@super -3@ mbar, later shown to be methane. In CRTs with oxide cathode, getter pumping action could be triggered by switching on the cathode heater, which efficiently cracked the methane generated. In CRTs with a FE tip, there was no way to decrease the residual methane pressure to the desired level. The FE tips, previously approved and characterised in UHV, were thus irreversibly damaged ab initio. In CRTs with NEGs, no pressure increase was registered by the SRG during several days. This means that they can maintain the residual atmosphere at the level that may provide a long-term operation of devices with diamond coated FE electron sources.