Low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon films

Abstract

The low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon (ta-C) films was investigated. Ta-C films prepared by a filtered arc deposition technique were annealed at 400 °C for 60-120 min in a nitrogen atmosphere. The density and sp3 content in as-grown film were 3.3 g cm-3 and ~90%, respectively. After annealing, no obvious changes in film density or sp3 content were observed. The threshold electric field of electron emission of annealed ta-C films increased. Through annealing the clustering of sp2 bonded carbon would occur, resulting in bandgap reduction and the eventual increase of the emission barrier. After a given annealing period, the degree of clustering increased, and was responsible for the threshold electric field increasing further. The results implied that the control of the sp2 bonding configuration in addition to the sp3 bonding is important in obtaining good emission properties for ta-C films.