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 muA/cm(2)) decreases from 3.9 to 1.5 V/mum after the sample is treated with hydrogen plasma for 30 min. High emission spot density of about 1.5 x 10(4) cm(-2) is achieved at an applied electric field 5.2 V/mum. 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. (C) 2003 Elsevier B.V. All rights reserved.