Farming at Nanoscale Dimensions

In order to direct self-assembly, we have to understand the physical stimuli that influence atoms to assemble in a certain way as they form a nanostructure. The particular nanostructures we find most interesting are called nanowires. These are long thin crystals whose amazing length-to-width ratio could help create very densely packed transistors. Using a combination of imposed patterning and self-assembly, we can grow nanowires spontaneously using the help of catalytic particles. And we can watch the nanowires as they grow, recording the process on video using a one-of-a-kind Ultra High Vacuum Transmission Electron Microscope in our lab.

We load a flat substrate into the microscope, place catalytic particles onto it (this is the directed part of the process), then heat it and add some reactive gases. We watch what happens to the catalytic particles (this is the self-assembly part of the process) by magnifying the image by 50,000 times or more. The reaction can be slow – it takes hours for the whole experiment to be finished – but the videos show how the nanostructures grow, one layer of atoms after another. Recording videos, for example at different temperatures or with different added gases, is central to understanding every step of the nanowires’ growth. We get to see cause and effect when the conditions change, so we can work out the laws of physics that control the growth. 

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