Nanotube Research
Carbon nanotubes have a range of unique and exciting physical properties and have, for the past two decades, received a great deal of attention from the scientific community. We are interested in understanding the atomic structure of nanotubes, their use in electronic devices, and their electron spin properties.
Nanotube Synthesis
We have used a wide variety of SWNTs, DWNTs and MWNTs from commercial sources, plus academic collaborators, made by pulsed laser ablation, arc-discharge, HiPCo, and chemical vapour deposition.
Within our laboratory, we have grown ultralong horizontally aligned carbon nanotubes on silicon wafers by CVD. These are suitable for field effect transistor device fabrication. The image shows SEM images of our horizontal SWNTs on silicon with alignment markers.
The SWNTs grow by the 'kite' mechanism, where they lift off the substrate and travel down-stream in the gas flow as the SWNT grows in length, resulting in long horizontal nanotubes in an insulating 300nm silicon dioxide substrate.
SWNTs grown across 1mm gaps.
Nanotube structure
We investigate the structure of carbon nanotubes using aberration corrected transmission electron microscopy (TEM). By operating the microscope at an energy of 80 keV it is possible to minimise the damage done to the carbon nanotubes during imaging.
We have shown that the stability of a single wall carbon nanotube (SWNT) under electron beam irradiation at an accelerating voltage of 80kV, is dependant upon their diameter, cleanliness, defect density and attachment to supports. Smaller diameter tubes are easily damaged by the electron beam.
The detailed atomic resolution of our TEM images has allowed us to reveal, for the first time, the remarkable atomic deformation mechanics of a SWNT. These results confirm that SWNTs behave as Timoshenko beams with shear strain occurring during flexing. The figure below shows (a) a chiral SWNT, (b) a zig-zag SWNT, and (c) higher magnification image of (b). For more information read the full text; Warner et al. Resolving Strain in Carbon Nanotubes at the Atomic Level, Nature Materials, 10, 958-962, (2011)
Nanotube electronic properties
The electronic behaviour of carbon nanotubes is strongly dependant on their precise atomic configuration with some tubes being semi-conductors and some metallic. We have fabricated high mobility solution processed SWNT field effect transistors and studied their correlations structural knowledge obtained from TEM.(below).
Nanoelectronic devices from horizontal CVD grown CNTs:
