An increase in the field emission from vertically aligned multiwalled carbon nanotubes caused by NH3 plasma treatment

We modified vertically aligned multiwalled carbon nanotubes (MWCNTs) grown on a Cu substrate by NH3 direct current plasma treatment for varying durations and investigated their microstructure and field emission properties. A great improvement on the field emission properties of the MWCNTs was obtained after the plasma treatment. Specifically, the MWCNTs after 1.0 min plasma treatment demonstrated the best field emission performance with the field enhancement factor increasing from 319 to 546, the turn-on electric field decreasing from 11.93 to 8.84 V/μm, and the highest emission current reaching 0.85 mA, as compared to the untreated sample. The improvement was attributed to the morphology change: the tapered structure of the MWCNTs generated by the plasma etching and the increased inter-tip distance due to the cluster structure of the thin tips. The open-ended tips and the increased structural defects introduced by NH3 plasma also played a role in the enhancement of field emission properties of the MWCNTs.