Life Testing of Patterned MWCNTs for use as a Field Emitter in a TOF Mass Spectrometer. Rachael A. Bis1, Stacy Snyder3, Bryan Hicks2, Jonathon Brame2, Stephanie Getty1, Todd King1, Patrick Roman1 and David Allred2; 1NASA Goddard Space Flight Center, Greenbelt, Maryland; 2Brigham Young University, Provo, Utah; 3Department of Physics, Lehigh University, Bethlehem, Pennsylvania.
Multi-walled carbon nanotubes are being evaluated as a field emitter material for the electron impact ionization source for a miniaturized time of flight mass spectrometer. A patterned array of MWCNT towers was grown by thermal chemical vapor deposition to form the cathode of a triode electron emission device. The MWCNTs were grown in vertical towers onto a silicon substrate to a height of approximately 10µm. Life testing was performed with the MWCNT grid using a triode configuration, where the MWCNT cathode is located 200µm from a grid electrode, and transmitted electrons are collected at an anode, 1.6mm from the grid. The cathode was negatively biased, compared to the grid and anode, and the emitted current was collected and measured independently at the grid and at the anode. Fowler-Nordheim tunneling behavior was observed, and a field enhancement factor of 900 was estimated. Life testing studies reveal that current was detectable at both the anode and the grid for over 500 hours. Stable current of 0.3µA was maintained at the anode for the first 350 hours of life testing, with reduced current of 0.06 µA for an additional 150 hours.