Comparative study of electron field emission from randomly-oriented and vertically-aligned carbon nanotubes synthesized on stainless steel substrates

Abstract

Randomly-oriented carbon nanotubes (CNTs) and vertically-aligned CNTs have been synthesized by a thermal chemical vapor deposition (CVD) process and a plasma enhanced CVD process, respectively, on stainless steel substrates without any external catalyst. Surface topography studies reveal that polishing and chemical etching result in favorable catalytic conditions for nucleation and growth of CNTs. Scanning electron microscopy and transmission electron microscopy observations reveal the growth of CNTs with catalyst particle at the tips. In comparison to randomly-oriented CNTs, vertically-aligned CNTs demonstrate better field emission properties with lower turn-on electric field of ∼2.0 V/μm, lower threshold electric field of ∼3.2 V/μm, and a 2.5-fold increase in the field enhancement factor. The vertical alignment of the emitters benefits the emission process by reducing the screening effect and streamlining the path of ejected electrons directly onto the anode. Vertically-aligned CNTs on conducting substrates are promising emitters in cold cathode vacuum electronics because of their direct contact with the substrate and efficient performance at low operating voltages.