Correlation between field electron emission and structural properties in randomly and vertically oriented carbon nanotube films

We investigated the influence of the structural properties of randomly oriented carbon nanotube (R-CNT) and vertically oriented carbon nanotube (V-CNT) films on their field electron emission properties. The R-CNT and V-CNT films were synthesized using FeNi catalysts by means of thermal and dual-RF plasma-enhanced chemical vapor depositions, respectively. The structural properties of the R-CNT and V-CNT films were dependent on the initial thickness of the FeNi catalyst. As the FeNi film thickness decreased, the diameters of both types of CNTs decreased. Although the field electron emission property of the V-CNT film was improved with increasing the aspect ratio of V-CNT, the field enhancement factor, beta, obtained from the Fowler-Nordheim plot was found to be 100 times larger than that obtained from the geometric properties. R-CNTs exhibited a lower threshold field than V-CNTs. These results suggest that the field emission property is markedly influenced by the surface state rather than by the geometric factors of CNTs.