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Summary form only given, as follows. A number of investigators have reported that coating silicon and metal substrates with several forms of diamond has led to significant improvement in the electron emission properties. We restrict this report to the effects on field electron emission from needle-shaped substrates before and after coating. Several forms of diamond and the influence of subsequent surface and thermal treatments were investigated. Needle shaped emitters were chosen because the same specimen could be extensively characterized by conventional field emitters methods before and after coating and/or after each subsequent treatment. The emitters are also conveniently shaped for detailed electron microscopic studies of the same interface and coating microstructure through which the emitted electrons must be supplied from the substrate. The substrates studied include: silicon, molybdenum, and nickel; diamond coatings were performed by: plasma CVD using bias enhanced nucleation and other nucleation techniques, as well as by dielectrophoresis, using different powders and thermal treatments. Surface treatments by O/sub 2/ and Cs were also investigated, as were several environmental ambients (including H/sub 2/ and D/sub 2/). Thermal treatment of the powders, after dielectrophoretic deposition was also studied in an attempt to maximize emission while retaining optimal stability.