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Nanostructures Imaged in 3-D

Photonics.com
Aug 2007
CLAYTON, Australia, Aug. 1, 2007 -- 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.3-DMicroscopySchematic.jpg
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


GLOSSARY
electron
A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.
image
In optics, an image is the reconstruction of light rays from a source or object when light from that source or object is passed through a system of optics and onto an image forming plane. Light rays passing through an optical system tend to either converge (real image) or diverge (virtual image) to a plane (also called the image plane) in which a visual reproduction of the object is formed. This reconstructed pictorial representation of the object is called an image.
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
mirror
A smooth, highly polished surface, for reflecting light, that may be plane or curved if wanting to focus and or magnify the image formed by the mirror. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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