Success stories
John Spencer and Kirsten Edgar: Synthesis of Carbon Nanotubes
In the protected environment of a quartz tube in a laboratory at Victoria University the creeping spidery arms of nanotubes self-assemble themselves into existence. Professor John Spencer and his PhD student Kirsten Edgar have initiated the growth of these fascinating nanoscopic structures. But what are nanotubes? You may ask and why are they growing in a Victoria University Laboratory? The answer is that these nanoscopic structures discovered only 13 years ago are all the rage on the science scene. In an age with increasingly vast amounts of information and increasingly small devices to process it, the properties of these uncommonly small, very strong, electrically conducting materials are irresistible. If it were possible to control the growth of these tubes so that their size, shape and position could be pre-determined they would open the doors to a whole nano-world of possibilities: nano-electronics, nanotweezers, nanolithography, nanotube reinforced composites, data storage, solar storage, noble radioactive gas storage; the list is endless. John and Kirsten, however are concerned only with the synthesis of nanotubes, understanding how they grow and trying to control the type and size of tube that grows.
There are so many different kinds of nanotubes: single wall, double wall, long, short, twisted, straight, skinny, fat and many more and the electronic and structural properties depend on these classifications. It is very difficult to sort the nanotubes once they are made so to get a single type of nanotube, required for a particular application the best idea is to control their growth from the beginning. This is the aim of research at Victoria University. It is, however no small task.
The essential elements for synthesizing carbon nanotubes are a volatile carbon source, a metal catalyst (with high surface area to grow the nano-tubes on) and a furnace to reach around 900°C. The nanotubes are grown inside a quartz tube in the furnace. Carbon vapour is fed into the tube from one end and the catalyst usually sits in a quartz boat in the middle. When this is all set up all they have to do is wait for the nanotubes to grow themselves. Carbon in the gas phase is absorbed into the metal catalyst (at these temperatures it moves through very rapidly) and somehow exuded as nanotubes from the catalyst surface. No one knows how this happens, which makes it extremely difficult to determine, let alone control what type of nanotube results.
A field of nanotubes
To get a particular type of nanotube it is important to have well defined catalyst centers. In other words, if the size of the catalyst particles vary the nanotube type will most likely vary too. Kirsten has come up with a new technique for applying the well defined catalyst particles. It is called electrospray. A solution of catalyst is charged in a capillary so that when released it repels itself creating a very fine mist. The solvent evaporates leaving fine catalyst particles around 12-50 atoms in size. Because this technique was developed here at Victoria University, Kirsten had to design and build all her equipment from scratch. She would have an idea and hand the plans over to Alan Rennie and Manu Pouajen-Blakiston in the workshop who turn them into reality. The electrospray technique has proved very successful. Nanotubes grow all over the walls of the quartz tube and they are beginning to be able to define the type that will grow.
Because nanotubes are so small you don't know what you've got until you look at them with a powerful microscope. The transition electron microscope (TEM) that was due to be installed at Victoria University arrived broken in its case late last year and was sent back. This has significantly slowed down the process. Kirsten has had to use the TEM at Wellington hospital instead. She also travels to Sydney to use their high resolution TEM. Raman Spectroscopy is also a very useful analysing tool. The vibrational peaks in the Raman spectrum can be used to determine the diameter of nanotubes and the purity of the sample.
As is often the case in the field of nano-technology very little is known about the principles on which these tiny structures behave. Before progress can be made in terms of applications, the foundations of understanding have to be layed. It is painstaking but step by step progress is being made paving the way for the nano-revolution to follow in its wake.
