Change of surface morphology and field emission property of carbon nanotube films treated using a hydrogen plasma

Large-scaled homogeneous multi-wall carbon nanotube (MWNT) films have been obtained at room temperature by a transfer technique. The surface morphology and microstructure features of the films before and after hydrogen plasma (HP) treatment were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and micro-Raman spectra. The electrical resistance in the temperature range 5–296 K and field emission in diode structure for the MWNT films were examined. Electron microscopy results demonstrated that the surface of treated nanotubes had become open palpus-like graphite layers or were covered by the onion-like carbon nanoparticles. The temperature dependence on electric resistance for MWNT films, which was fitted by three-dimensional variable range hopping conduction, was observed; and the slope and scope of the temperature dependence for the treated film were larger than that of the untreated one. The field emission tests indicated that the turn-on field (at 0.1 mA/cm2) decreases from 3.9 to 1.5 V/mm after the sample is treated with hydrogen plasma for 30 min. High emission spot density of about 1:5 104 cm 2 is achieved at an applied electric field 5.2 V/mm. The conversion mechanism of the treated carbon nanotubes(CNTs) microstructure and the reason for the change of electronic properties and field emission of MWNT films were discussed. # 2003 Elsevier B.V. All rights reserved