Improved crystallinity of double-walled carbon nanotubes after a high-temperature thermal annealing and their enhanced field emission properties

High-purity double-walled carbon nanotubes (DWCNTs) were synthesized by catalytic decomposition of CH4 over Fe-Mo/MgO catalyst at 900 degrees C. After purification, the DWCNTs were annealed at 1300 degrees C in vacuum condition of 10(-5) Torr. The DWCNTs before and after the high-temperature thermal annealing were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. It was observed that the annealed DWCNTs had enhanced crystallinity and reduced defects. In addition, the DWCNTs showed better field emission performance after high-temperature thermal annealing. The annealed DWCNTs indicated the turn-on field of about 1.16 V/mu m at 0.1 mu A/cm(2) and the threshold field of about 2.12 V/mu m at 1.0 mA/cm(2). Moreover, the annealed DWCNTs exhibited better emission stability compared with the nonannealed DWCNTs. Such a remarkable improvement of field emission performance was attributed to the enhanced crystallinity and reduced defects of the annealed DWCNTs.