Nanostructures Imaged in 3-D

An optical technique more than a century old has helped solve a major problem with surface electron microscopy -- the inability to receive depth information about a sample -- and now allows fast-moving nanostructures to be imaged in three dimensions and in real time.

Monash University physicists David Jesson, Konstantin Pavlov and Michael Morgan solved the problem by developing a new technique that incorporates an experiment from the 1800s to determine surface shape and depth. The breakthrough will enable scientists to see, in real time, fast-moving images of the tiniest droplet or the smallest structure evolving and be able to see how they behave and interact on surfaces.

Schematic showing how a 3-D line profile (white line) can be obtained from Lloyd's fringes in surface electron microscopy. (Image courtesy Monash University)

"How materials develop and react with other materials forms the basis of a great deal of scientific research, and what we have achieved is the ability to view small clusters on surfaces as they are evolve and interact," professor Jesson said. "Previously, scientists have had to freeze-frame each image by removing specimens from the growth or heating environment and link them together. Our discovery means that images can be now captured as a real-time video which also shows the depth of the structure. This will open up new opportunities for theorists to model and understand the changes in nanostructures being developed for a new generation of computers, lasers and communication systems, and is a new tool for studying surface shape dynamics on small-length scales."

Jesson's team discovered 3-D imaging of nanostructures is possible while using photoemission electron microscopy, or PEEM, to look at droplets of liquid gallium sitting on a mirror-flat surface of gallium arsenide.

"We created interference fringes by illuminating the droplets with ultraviolet light using a classic 19th century physics experiment known as Lloyd's Mirror, where light reflected off a mirror interferes with light coming directly from the source," he said.

They found that the bright interference fringes result in the emission of electrons which can be imaged using a surface electron microscope. Applying the same principle as viewing a standard topographic map of a mountain range, they were able to determine the height of the structure by counting the contour lines.

"Fringes are sensitive to the 3-D shape of the gallium droplets and are distorted by the electric field due to the topographic features. This can then be corrected using image processing, to provide a real-time relief map showing how the surface of the metallic droplets evolves," Jesson said.

This work was recently published in Physical Review Letters 99 and is also featured in the Physical Review Focus of the American Physical Society.

For more information, visit: www.monash.edu.au/news