APPLIED RESEARCH IN THIN-FILM FIELD-EMISSION TUBES.
Abstract:
Recent progress in the development of micron-size field emission diodes is reported. There has been a continuing difficulty in forming asperities on the molybdenum areas at the bases of micron-diameter cavities despite good results with bare molybdenum films. During this quarter, investigations of source-to-substrate configurations confirmed that asperity density is dependent on the angular displacement of the source and substrate axes used during the deposition of molybdenum cathode films. Also, it was found possible to grow asperities on molybdenum films deposited at normal incidence to the substrate but originating from source areas in the range from about 20 degrees to 50 degrees relative to the source axis. The influence of the vacuum environment, substrate temperature during molybdenum deposition, and aluminum thickness were then investigated for a fixed configuration 45 degrees source angle, normal incidence on substrate. The results indicate the following asperity growth is optimum in residual gas pressures of the order of 0.000001 torr the aluminum thickness should be about 200A or less and the growth process is insensitive, over wide limits, to the substrate temperature used during molybdenum deposition. Moreover, it was found possible to grow asperities on a molybdenum surface over which aluminum oxide had previously been deposited and etched away i.e., similar to the molybdenum areas at the bottoms of cavities without the necessity for first depositing a fresh layer of molybdenum. Specimens with micron-diameter diode cavities have been subjected to the asperity formation process and are awaiting electrical tests for field emission activity. Author