Thin multi-walled carbon nanotubes synthesized by rapid thermal chemical vapor deposition and their field emission properties

Thin multi-walled carbon nanotubes (MWCNTs) were successfully synthesized by a rapid thermal chemical vapor deposition (RTCVD) method using a liquid catalyst. The growth of the thin MWCNTs was achieved by decomposition of C ₂H ₂ over Fe-Mo/MgO/citric acid directly at 700 °C for 30 min. Most thin MWCNTs, which had about 6~8 graphene layers, showed high purity (~90%) and good crystallinity. Moreover, they showed homogenous morphology and uniform diameters. The average outer diameter of the thin MWCNTs was about 8 nm. The uniform diameter and good homogeneity of thin MWCNTs were mainly attributed to prevention of catalyst agglomeration at high temperature due to a short reaction time, and the high purity of thin MWCNTs was caused by suppression of the residual CNT growth after finishing a reaction in RTCVD process. Field emission properties of the thin MWCNTs were measured in a vacuum chamber at a pressure of less than 2 ? 10 ^-7 Torr. The turn-on field was about 3.35 V/μ, at the emission current density of 0.1 μ?/cm2, and the emission current density was 2.5 mA/cm ² at an applied field of 6.7 V//i,m. Particularly, the thin MWCNTs showed strong emission stability at emission current density of 0.8 mA/cm ² for 20 h.