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A comprehensive investigation has been carried out to determine the source of an inherent temporal instability in the spatial distribution and the electron emission current obtained from field electron-emitting carbon fiber tips of type Polyacrylonitrile VPR – 19, thermally treated at 2800 °C. These instability effects have been successfully overcome by coating the carbon fiber tip with a sub-micron layer of dielectric polystyrene coating. The influence of the coating thickness was studied and an optimum thickness of (0.1–0.2) μm that produced high emission stability and found to possess the significant reduction in the intensity fluctuations of the field electron emission patterns. The current-voltage characteristics, Fowler-Nordheim plots, Murphy-Good plots and the scanning electron micrographs in addition to the field electron emission patterns were used in this investigation to study the emission characteristics of carbon fiber tips before and after samples are being coated with polystyrene dielectric layer. Comparison between the emission process from the clean and composite tips are reported and the current-voltage characteristics were obtained at a threshold field that is a few times lower than that of the clean tip. At low emission current levels linear Fowler-Nordheim and Murphy-Good plots were obtained with a slope value lower than that of the clean tip. The spatial distribution consisted of a very bright spot without any internal structure. Experiments have also shown that the coated tips are not affected by the variations of pressure conditions down tombar. These results suggest that a polystyrene coated fiber tip offers better performance than the clean carbon fiber tip as a new field electron emission source.

Influence of polystyrene layer on the field electron emission performance of nano-apex carbon fibre emitters