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

摘要

We report on the application of Atomic Force Microscopy (AFM) for studyingthe Field Emission (FE) properties of a dense array of long and verticallyquasi-aligned multi-walled carbon nanotubes grown by catalytic Chemical VaporDeposition on a silicon substrate. The use of nanometric probes enables localfield emission measurements allowing investigation of effects non detectablewith a conventional parallel plate setup, where the emission current isaveraged on a large sample area. The micrometric inter-electrode distance letachieve high electric fields with a modest voltage source. Those featuresallowed us to characterize field emission for macroscopic electric fields up to250 V/$\mu$m and attain current densities larger than 10$^5$ A/cm$^2$. FEbehaviour is analyzed in the framework of the Fowler-Nordheim theory. A fieldenhancement factor $\gamma \approx$ 40-50 and a turn-on field $E_{turn-on}\sim$15 V/$\mu$m at an inter-electrode distance of 1 $\mu$m are estimated.Current saturation observed at high voltages in the I-V characteristics isexplained in terms of a series resistance of the order of M$\Omega$. Additionaleffects as electrical conditioning, CNT degradation, response to laserirradiation and time stability are investigated and discussed.