Arrays of vertically aligned tubular-structured graphene for flexible field emitters

Abstract

Arrays of tubular-structured reduced graphene oxide (RGO) were fabricated by a simple method involving filtration of a solution containing highly dispersed RGO sheets. The length and alignment of the tubular-structured RGO arrays were controlled by the filtration rate and by tuning the interactions between the hydrophobic RGO sheets and the porous walls, rather than the top surfaces, of the polycarbonate filter membrane. As expected, the lengths of the RGO arrays increased with higher filtration rates; however, maximum field emission characteristics were obtained at an intermediate filtration rate because field screening reduced electron emission from the longer-length RGO arrays. ZnO-coated RGO arrays showed excellent emission stability without significant current degradation or fluctuations, even under O₂ exposure. The ZnO layer protected the emission site of the RGO arrays from the reactive ion bombardment of oxidative gas species. Moreover, the RGO arrays were highly flexible with preservation of the field emission properties, even at large bending angles. The excellent field emission characteristics of the tubular structured RGO arrays were attributed to the high crystallinity, abundant sharp edges, and the chemical stability of the RGO arrays, as well as the strong interactions between the RGO arrays and the substrate.