New understanding of 'holy grail' nanowire technology

New computer simulations can now replicate the way nanoclusters (above) behave at the nanoscale.

After several years of exhaustive research, computer simulations developed by IRL's nanotech modelling group, headed by Shaun Hendy, can now replicate the way molecules behave at the nanoscale.

Nanoscience and nanotechnology encompass a range of techniques across the whole spectrum of science, physics, medicine, engineering and chemistry. However, molecular nanotechnology, the science of manipulating atoms and molecules to build new material atom by atom, is completely different.

Molecular-based electronic devices, such as hydrogen or methane sensors and computer chips, need extremely fine wires, called interconnects, to hold all the components together, and it is the technology for constructing these interconnects that has, until now, proven so elusive.

Shaun Hendy says that the familiar laws of physics don’t apply at this level, meaning matter behaves in strange and unpredictable ways.

“The difficulty with nanotechnology is that when you’re trying to assemble very small things you can’t watch the process and see what’s happening in real time. You can look in the microscope at the beginning of the process and again at the end but you have to guess what’s going on in between. What we do is fill in that gap using computer simulations to find out what’s happening,” he says.

“The advantage is that we can then see what’s happening all the way through and if a client wants to know what would happen if they did something slightly differently, we can test it in an afternoon, whereas they would have had to do a big experiment that could have taken a couple of months to set up.”

The nanowires are made by blowing tiny clusters of metallic nanoparticles, called nanoclusters, into trenches etched into insulating substrates within a vacuum chamber. If the velocity of the nanoparticles is tuned correctly, the nanoparticles will bounce off parts of a surface that are flat, yet stick to parts of a surface that have been pre-patterned. Nanoscale electronic devices can then be assembled by prepatterning surfaces and depositing nanoparticles at the right velocity.

Nanoparticles are ultra-small, less than 100 nanometres wide (a single human hair is around 80,000 nanometres in width), and can only be seen with an electron microscope. They are everywhere in nature and are used worldwide in an array of scientific and technical applications, such as sunscreen and cosmetics.

Christchurch-based start-up company, Nano Cluster Devices has been using IRL’s simulations in their development of a hydrogen sensor – the first of what Simon Brown, NCD’s Executive Director hopes will be a comprehensive range of products using the self-assembling nanowire technology.

“When nanoparticles touch each other they coalesce, or merge, like two droplets of water do on the wall of your shower,” says Simon Brown.

“Most of us are used to looking at things in the macroscopic world and we don’t expect two soccer balls, for example, to coalesce into each other. At the nanoscale however, lots of things are very different. The input from Shaun and his team has been crucial to our understanding of the processes involved in creating our nanowires.

“This new technology means that our hydrogen sensors, and others such as sensors for methane or ammonia, for example, could be made at a fraction of the cost of a conventional sensor. They are also expected to be faster, have greater sensitivity and be more reliable than conventional sensors,” he says.

Other applications for the self-assembling nanowire technology are in the semiconductor industry, such as interconnects for silicon chips. Nano Cluster Devices has worked very closely with Texas Instruments, a large US chip manufacturer, and with Novellus, a large supplier of equipment to the semiconductor industry.

“This is a flagship nano-electronics project for us, says Shaun Hendy. "Molecular nanotechnology is very new and this project will hopefully have spinoffs in other areas – for example, we’ve been able to use this capability in our nanoparticle modelling work with Victoria University.

“Being the pioneers, if you like, in an emerging technology which could have such a global impact – it’s very exciting.”