A local field emission study of partially aligned carbon-nanotubes by atomic force microscope probe

Atomic force microscopy (AFM) was used to study the field emission (FE) properties of a dense array of long and vertically quasi-aligned multi-walled carbon nanotubes grown by catalytic chemical vapor deposition on a silicon substrate. The use of nanometric probes enables local field emission measurements to be made allowing the investigation of effects that are not detectable with a conventional parallel plate setup, where the emission current is averaged over a large sample area. The micrometric inter-electrode distance allows one to achieve high electric fields with a modest voltage. These features made us able to characterize field emission for macroscopic electric fields up to 250 V/mu m and attain current densities larger than 10(5) A/cm(2). FE behaviour is analyzed in the framework of the Fowler-Nordheim theory. A field enhancement factor y approximate to 40-50 and a turn-on field Eturn-on similar to 15 V/mu m at an inter-electrode distance of I pm are estimated. Current saturation observed at high voltages in the I-V characteristics is explained in terms of a series resistance of the order of MO. Additional effects, such as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed. (C) 2007 Elsevier Ltd. All rights reserved.