Optimization of Vertically Aligned Nature of CNTs for Improved Field Emission Behavior

Abstract

For improved field emission behavior, we demonstrate the PECVD technique to grow highly ordered, selectively grown, vertically aligned carbon nanotubes (CNTs) with optimum density. We report the optimization of vertically aligned CNTs by optimizing catalyst thickness, dot size of catalyst and the spacing between them.

We made an attempt to optimize the catalyst thickness to understand the effect over density, diameter and height of CNTs. SEM images reveal that the catalyst thickness as well as the dot size and the spacing is helpful in optimizing the vertical alignment of CNTs. The vertically aligned CNTs provide a large number of tips as compared to horizontally aligned CNTs over an area. Also, the high value of the enhancement factor required to achieve a better FE behavior is also plausible with vertical CNTs. The field emission results confirm that the vertically aligned CNTs bring a large current density at relatively low threshold field. We were able to achieve a current density of 100 mA/cm² at a field of 6 V/µm. Density and therefore screening effect also becomes important factors that hinder the performance of CNT‐based emitters. However, in our typical samples we observed less discrepancy in the density, and the density so calculated was in the order of 10⁹/cm².

Keywords:

• Carbon nanotubes
• Field emission
• Screening effect
• Vertical alignment of CNTs

ACKNOWLEDGMENT

The authors wish to acknowledge Mask fabrication group, Silicon Group and MMIC division of Solid State Physics Laboratory for mask fabrication, photolithography over silicon & SEM characterization of grown carbon nanotubes.