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

TL;DR

This study uses AFM probes to locally measure field emission from aligned carbon nanotubes, revealing detailed emission properties and effects not observable with traditional methods, including high current densities and stability factors.

Contribution

It introduces a novel AFM-based approach for local field emission measurement of aligned carbon nanotubes, providing detailed insights into their emission behavior and stability.

Findings

Achieved high electric fields up to 250 V/μm with current densities >10^5 A/cm^2.

Estimated a field enhancement factor of 40-50 and a turn-on field around 15 V/μm.

Observed current saturation explained by series resistance of about MΩ.

Abstract

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/$\mu$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 $\gamma \approx$ 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 is explained in terms of a series resistance of the order of M$\Omega$. Additional effects as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed.