摘要
In chemical vapor deposition (CVD) of carbon nanotubes (CNTs), formation and density control of nano-sized catalysts is critical in obtaining vertically aligned nanotubes. Two commonly adopted methods of achieving catalytic nanoparticles are heat-treatment and plasma pretreatment of a catalytic thin film. In this study, the CNTs were grown inside silicon trench arrays utilizing microwave plasma CVD. The effects of hydrogen plasma pretreatment of the nickel catalysts on the growth of CNTs and their subsequent field emission characteristics were investigated. Without plasma pretreatment, randomly oriented, short CNTs with low tube density grew. With plasma pretreatment, vertically aligned and highly dense CNTs were observed to grow but longer pretreatment resulted in shorter CNTs. The plasma pretreatment technique was successfully employed to achieve gated CNT microcathodes with a convex-shape surface profile, having quasi-uniform electric field distribution on the CNT tips. CNT sample with 1-min pretreatment exhibited the lowest turn-on field of ∼5 V/μm and achieved a current density of 1.0 mA/cm 2 at a threshold field of 8.0 V/μm. Overall, the hydrogen plasma pretreatment has been demonstrated to be a useful technique for the synthesis of vertically aligned CNTs and surface profile tweaking in gated structures. © 2006.