Solid-state fabrication of ultrathin freestanding carbon nanotube–graphene hybrid structures for field emission applications

Abstract

A solid-state method was developed to fabricate field emission (FE) devices composed of freestanding and ultrathin carbon nanotube (CNT)–graphene nanoribbon (GNRs) hybrid emitter arrays that function as cathodes. The array was made by using a laser to irradiate the freestanding 200 nm-thick CNT films. The FE devices had lateral structures with the electron beam being generated by the 1D emitter arrays. The device was able to generate an emission current of 846 μA, which is equivalent to one emitter generating 150 nA at 200 V. The high FE performance is attributed to the ultrathin nature of the array coupled with the well-separated emitters. This remarkably improved the field penetration and effectively reduced the screening effect. Additionally, the emitter array had the hybrid structure of double-walled CNTs and GNRs, both of which have exceptional electron emission ability due to their unique graphitic structures. The influence of the anode–cathode distance (AC distance) on the FE performance was investigated. When the AC distance increased, the plot of emission current against applied voltage shifted toward higher voltage. However, the plot of current density against electric field (that is, the voltage normalized by the AC distance) shifted to the lower field regime. Therefore, the threshold field at which the current density reached 1 mA/cm2 decreased as the AC distance increased. This resulted from the increase in the corresponding field enhancement factor.