A local field emission study of partially aligned carbon-nanotubes by AFM probe

We report on the application of Atomic Force Microscopy (AFM) for studying 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 allowing investigation of effects non detectable with a conventional parallel plate setup, where the emission current is averaged on a large sample area. The micrometric inter-electrode distance let achieve high electric fields with a modest voltage source. Those features allowed us to characterize field emission for macroscopic electric fields up to 250 V/$μ$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 $γ\approx$ 40-50 and a turn-on field $E_{turn-on} \sim$15 V/$μ$m at an inter-electrode distance of 1 $μ$m 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 M$Ω$. Additional effects as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed.

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