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Nonlinear Fowler–Nordheim plots of the field electron emission from graphitic nanocones: influence of non-uniform field enhancement factors

Well-aligned graphitic nanocones were synthesized on polished pristine p-type (100) silicon wafers through plasma enhanced hot filament chemical vapour deposition. The field electron emission properties were investigated using anode probes of different diameters. Non-linearity was observed in the field electron emission (FEE) Fowler–Nordheim (FN) plots at high electric field. The numerical calculations based on the superposition of two types of characteristic emission sites are consistent with the experimental data. The non-linearity in the FN plot may be attributed to the non-uniform field enhancement factor (FEF) of the graphitic nanocones. At low electric field, electrons are emitted mainly from nanocones with large FEF, corresponding to a small slope magnitude in the FN plots. With the increasing electric field, the nanocones with small FEFs also contribute to the emission current, which results in a reduced average FEF and so a larger slope magnitude. If the difference in FEFs of the two types of emission sites is large, the emission sites with smaller FEF may not be able to participate in emission even at the highest electric field tested in the experiments and the FN plot remains a straight line determined presumably by the emission sites with larger FEF.