Field Emission from Multi-walled Carbon Nanotubes and its Application in Nanoelectromechanical Systems

Doktorsavhandling, 2006

Films of aligned multi-walled carbon nanotubes (MWCNTs) are interesting for applications such as cold emission cathodes in flat-panel display technology and in lighting elements. MWCNTs are, besides this, good candidates to be used in nanoelectromechanical systems (NEMS). Films consisting of MWCNTs have been fabricated using two different methods, thermal chemical vapour deposition (TCVD) and plasma enhanced chemical vapour deposition (PECVD). The results from electron field emission measurements show that high electron emission currents lead to ohmic heating and induce irreversible changes in the MWCNT films. The heating is higher for TCVD films compared with PECVD films, and can be explained by the poorer quality MWCNTs produced by TCVD. Spectral measurements of the emitted light from the films show black-body radiation corresponding to temperatures ranging from 1500-2200 K for the TCVD films. These high temperatures lead to degradation and emitter failure and can be a problem for future industrial applications. In addition, individual MWCNT have been investigated using a combined scanning tunnelling microscope (STM) and transmission electron microscope (TEM). In these experiments we observed an enhanced electron emission due to the resistive heating that increases the emitter temperature and gives a non-linear Fowler-Nordheim plot for high emission currents. The second subject of this thesis concerns the ability to use MWCNTs in NEMS. The realisation and experimental measurements of a three terminal nanorelay show that, by applying a gate voltage, a MWCNT can be electrostatically deflected. In the given design, the tip of the nanotube was moved to establish physical and electrical contact with a drain electrode. This structure is suggested to work as a switch operating at GHz frequency, having very low dissipation. Other applications, suggested by the theoretical calculations, are e.g. tunable filters for GHz signals. However, high frequency measurements are still to come.