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The dance of the droplet

10 June 2009

The Low Energy Electron Microscope

Monash scientists have discovered a new way that liquid droplets move on surfaces that requires no surface modification or external forces - a discovery made possible by a high-tech microscope that records surface dynamics.

The world-first discovery was recently published in the prestigious journal Science.

Using the Low Energy Electron Microscope (LEEM) Professor David Jesson and Dr Wen Xin Tang from the School of Physics evaporated gallium arsenide - a semiconductor used in technology - to discover the new type of droplet motion.

"Droplet motion is seen in everyday life; rain droplets running down a window pane or liquid drops moving about on a hot plate," Professor Jesson said.

"While most droplet motion is due to a range of outside factors - such as changes to surfaces or external forces - we’ve been able to show that none of these elements are actually required to move a droplet, providing new physical insight into how surfaces evaporate and can unexpectedly propel droplet motion."

Professor Jesson said the LEEM combined a surface electron microscope with a semiconductor growth system that allowed the team to deposit materials one atomic layer at a time and record the growth processes in ultra-high vacuum.

"By making real-time movies of surface dynamics we are able to better understand the underlying physics governing droplet formation and see things that no-one else has seen - hence the moving drops," Professor Jesson said.

"Researchers already know how to re-crystallise droplets under arsenic.

"This discovery may allow us to use surface features such as steps to guide droplets into position and then re-crystallise them, thus creating new gallium arsenide quantum structures in the positions we want for new applications in areas such as quantum computing."

The Monash team is working with Dr Jerry Tersoff of IBM (USA) on the project.