Tests were performed on FEPET, Inc. carbon thin film cathodes to characterize lifetime, resistance to environmental conditions, and performance stability. The cathodes were found to exhibit half lifetimes on the order of 7000 h in sealed glass envelopes. Operation in oxygen and water were found to degrade the cathode performance severely. Xenon had no effect on the cathode lifetime or stability, demonstrating its resistance to ion sputtering. During characterization in vacuum systems, initial turn on was quick and stable. Carbon thin films are suitable cathode materials for display, microelectronic, and ion propulsion uses.