In-situ Field Emission Characterisation of Multi-walled Carbon Nanotubes
The field emission (FE) properties of groups of carbon nanotubes (CNTs), an individual CNT and from a single gated CNT are measured using nano-manipulators fitted within a scanning electron microscope (SEM). We investigate the effect of the anode locations at anode to emitter tip distances as low as 1 μm.
Nano-manipulators were installed within an SEM chamber, and sharpened probes with an end radius of 5 μm were attached to the end of the two manipulators. The minimum step size achievable was 40 nm, with the FE performing within the SEM chamber at a vacuum pressure in the range of 10-7 Torr. The figure shows the 2 nano-manipulators within the SEM chamber. The sequence of images show one of the probes placed accurately above a single CNT.
A group of multi-walled CNTs were attached randomly to the end of a carbon fibre and their field emission characteristics recorded. It was noted that the position of the anode (which could be measured accurately within the SEM) played an important role in the performance of the emitter. Both threshold field and enhancement factors were affected only at low anode to emitter tip separations. To further our studies we performed similar emission experimentation on an isolated CNT. A CNT polystyrene polymer was physically broken to expose a CNT and its edge scanned to find a suitable emitter. Field screening effects due to adjacent emitters were removed by our ability to selectively burn off, or pull out unwanted CNTs. During FE testing the electron beam was turned off so as not to influence our results. FE testing was conducted on groups of CNT and a single CNT. Three terminal measurements were also performed on an isolated CNT.
