Enhancement of electron field emission from density-controlled carbon nanotubes

In this study, we investigated the effect of catalyst pretreatment by NH3 plasma on the growth of CNTs by plasma-enhanced chemical vapor deposition and their field emission properties. Thickness of catalytic Ni was varied from 5 to 100 angstrom. It was found that the catalyst nanoparticles which were essential for the CVD synthesis of CNTs were formed well after plasma pretreatment and the size of the nanoparticles was strongly dependent on the Ni thickness and plasma pretreatment. In field emission measurement using diode-type configuration, the low-density and smaller-diameter CNTs synthesized from Ni catalyst layer after NH3 plasma pretreatment showed a smaller electric-field-screening effect, which, in turn, increased the field enhancement factor by a factor of 4 compared with as-grown CNTs from Ni without plasma pretreatment. CNT emitters obtained from plasmapretreated 25-angstrom-thick Ni catalysts showed excellent field emission characteristics with a very low turn-on field of 1.1 V/mu m at 10 mu A/cm(2) and a high emission current density of 1.9 mA/cm(2) at 4.0 V/mu m, respectively. In addition, experimental results revealed that the catalyst thickness might be optimized for electron emission efficiency.