ZnO quantum dots decorated on optimized carbon nanotube intramolecular junctions exhibit superior field emission properties

Abstract

Highly efficient carbon-based 1D light-emitting devices require multi-quantum well heterostructures with sensitive optical properties. However, carbon nanotubes (CNTs)-based composites become much worse than expected and most of their applications such as field emission are thwarted because dispersing CNTs among one another is difficult. We demonstrate that such sensitive optical and limited field emission properties can be attained and improved, respectively, through the use of ZnO nanocrystal selective quantum well heterostructures grown on carbon nanotubes to fabricate carbon-zinc-oxide (CZO) nanotubes. ZnO can be effectively and uniformly decorated on the carbon nanotubes intramolecular junctions with abundant functional groups and also with large surface adsorption area produced by CNTs surface plasma pre-treatments at room temperature. The cathodoluminescence (CL) spectrum of the CZO nanotubes exhibits a weak UV emission peak and two distinct strong green emission peaks at 2.51 eV and at 2.4 eV, attributed to zinc-rich ZnO band-to-donor transitions and oxygen-rich ZnO band-to-acceptor transitions, respectively. Furthermore, the CZO nanotubes reach an extremely low turn-on field of 0.1 V μm⁻¹, low threshold field of 3.1 V μm⁻¹, but high field enhancement factor β of 110 × 10³. The field emission properties are dramatically enhanced by ZnO quantum dots decorated on the carbon nanotube intramolecular junctions, which not only provide extra electron emission paths and higher carrier concentrations, but also protect the emitter from ion bombardment during operation.