Formation, cathodoluminescence and field emission of ZnO quantum dots attached on oxygen plasma activated carbon nanotubes

A simple method to grow uniform ZnO quantum dots homogenously on the whole surface of multi-wall carbon nanotubes (MWCNTs) with oxygen plasma activation was reported in this work. The ZnO quantum dots can be successfully grown without catalyst using and well attached on the whole surface of MWCNTs with 20 s oxygen plasma treatment (O20). The ZnO quantum dots are uniform in the diameter of ~15 nm, and exhibit a single crystalline hexagonal wurtzite structure with lattice fringe of ~0.52 nm and growth direction along the [0001] axis from XRD and HRTEM results. Auger electron spectroscopy results show that the elemental composition of Zn on O20 sample can reach up to 43.8%, and the Zn/O ratio is ~1. From cathodoluminescence results, O20 sample shows a small ratio of green emission intensity to ultra-violet emission intensity, revealing that O20 sample has a highly crystalline structure with fewer oxygen deficiencies. ZnO quantum dots attached on MWCNTs with longer durations of oxygen plasma treatment result in a slight blue shift of both UV and green emission. Besides, O20 sample also reveals outstanding field emission properties (turn-on field of 0.27 V/μm, threshold field of 3.24 V/μm, field enhancement factor of 11897) greater than pristine MWCNTs (turn-on field of 4.39 V/μm, threshold field of 6.16 V/μm, field enhancement factor of 1582). Therefore, ZnO quantum dots attached on oxygen plasma activated carbon nanotubes successfully combine the particular advantages of ZnO and MWCNTs.