Effect of Cathode–Anode Distance on Field Emission Properties for Carbon Nanotube Film Emitters

The influence of the cathode–anode distance (gap) on field emission (FE) properties is investigated for carbon nanotube film emitters. Any increase in the gap can cause a clear shift in the plot of emission current (I) against applied field (EA) (I–EA curve) to the low field regime, resulting from an increase in the corresponding field enhancement factor (βFN). However, normalization of these I–EA curves through the use of the local field (EL) concept shows that the emission sites are invariant during a change in the gap, although they attain stronger EL at larger gaps. When a modified Fowler–Nordheim plot [ln (I/EA2)–2ln βFN vs 1/EA] is employed, the plots obtained at various gaps provide a unique intercept with the vertical axis, consistent with the experimental data measured at differing gaps.