Understanding parameters affecting field emission properties of directly spinnable carbon nanotube webs Original Research Article

The electron field emission (FE) properties of highly aligned carbon nanotube webs (CNTWs) spun directly from carbon nanotube forests are elucidated in this study. By controlling the synthesis parameters, a series of CNTWs with different structural properties are synthesized and the effect of web areal density and the length of the constituent nanotubes on the field emission property studied. An empirical/analytical factor (Tip Factor, T) is developed which relates the structural properties of the web to their effect on the effective concentration of free nanotube ends, and hence on FE. The validity of T as a measure of tip concentration is further demonstrated by measuring the pull-off adhesive forces using an AFM-based technique. Both FE and mechanical adhesion are linearly related to T. These results suggest that in order to achieve the highest field emission or dry adhesion webs, features desired include short nanotubes, with dense and even coverage of the surface.