Empirical Investigation of Carbon Nanotube Pillar Array Field Emitter Geometry for Increased Current Densities

Since their discovery in 1976 and detailed report in 1991, carbon nanotubes (CNTs) have gone through a great deal of research devoted to studying their extraordinary properties and applications. The high aspect ratio structure of CNTs, their chemical stability high thermal conductivity, and mechanical strength, are attributes that make CNTs excellent candidates for cold field emitters. CNTs are capable of achieving longer lifetime and higher current densities at lower applied fields, thus making them highly attractive for field emission applications requiring high current densities. However, until now, fabricating stable and robust CNT cold field emitters has been very difficult while simultaneously achieving economical manufacturing. The high current density required for certain applications such as microwave amplifiers still remain a tremendous challenge.;In spite of the progress made in recent years on understanding the fundamentals of CNT emitters and on how to implement CNTs in applications requiring electron sources, wide-scale adoption remains elusive. There are still many factors that contribute to the CNT emission process which arc not fully understood, particularly with respect to achieving optimal emission current and emitter stability. Phenomena such as field screening, local field enhancement and the edge effect have been explored in the last few years. For many applications where CNT emitters can be implemented, several of the above mentioned phenomena have not been fully explored. Previously, we have demonstrated that CNT pillar arrays (CPAs) offer a practical solution for the fabrication of stable and easy to manufacture CNT cathodes. A CNT pillar is described as a uniform, highly dense, vertically aligned, compact bundle of CNTs. Vertical self-alignment of CNTs results from the van der Waals interaction between neighboring CNTs and contributes to the excellent structural stability of CNT pillars. These CNT pillar structures exhibit lower turn-on fields and a higher current density when compared to that of continuous CNT films. In this work, we explore the structural effects of CNT emitter arrays on the field emission properties of the CNT cathodes. The geometry of each pillar was specifically chosen to investigate the effect of the cathode geometry on the electric field enhancement at the edges of the structure This enhancement effect is called the "edge effect" and can be described as a phenomenon where the electric field is enhanced along the edges of a CNT pillar structure. By varying the geometry of the pillar structures, we now have a means to increase emission current density.