Effects of annealing Ni catalyst in nitrogen-containing gases on the surface morphology and field-emission properties of thermal chemical vapor deposited carbon nanotubes

Abstract

Ni catalyst was annealed in N 2O/N 2/NH 3 in order to study the effects of the annealing on the surface morphology and field-emission characteristics of synthesized carbon nanotubes (CNTs). The morphology and composition of the CNTs show that the grain size and composition of the Ni catalyst can be modified by N 2O, N 2, and NH 3 pretreatments. Scanning electron microscopy images of evaporated Ni after N 2O pretreatment show that the Ni particles are more uniformly distributed, and their sizes are relatively small. It is found that the CNTs grown on Ni pretreated with N 2O have the highest surface density and the highest emission current. This improvement is accomplished through the more uniformly distributed and smaller Ni particles obtained by N 2O pretreatment. The growth of amorphous carbon is also suppressed. The reasons for this improvement are that nitrogen and oxygen atoms dissociated from N 2O in the pretreatment can oxidize the catalyst particles and inhibit their growth so that the resulting Ni metal nuclei become smaller and more uniformly distributed, which is beneficial to CNT growth.