Nanoparticles Viewed in 3-D

A new x-ray microscope has been devised that can, for the first time, examine nanoparticles -- materials smaller in scale than one billionth of a meter -- in three dimensions. The device could be used to make better materials for electronics, optics and biotechnology applications.

Subhash Risbud, professor of Chemical Engineering and Materials Science at the University of California, Davis; John Miao of UCLA and colleagues from Japan and Taiwan published a paper in Physical Review Letters on Nov. 21 describing the new microscope and technique.

Transmission electron microscopy (TEM) has traditionally been used to study nanomaterials, but because electrons do not penetrate far into materials, the sample preparation procedure is usually complicated and destructive. Another disadvantage is that TEM only provides two-dimensional images.

The new method shines a powerful x-ray source onto a nanoparticle and collects the x-rays scattered from the sample. Then computers construct a three-dimensional image from that data. The microscope can resolve details down to 17 nm, or a few atoms across.

Using the new microscope, Risbud and colleagues were able to take detailed 3-D pictures of a quantum dot of gallium nitride, and also to study the structure inside it at a nanometer scale. Quantum dots are tiny particles that change their optical and electronic properties, depending on the particle size. Gallium nitride quantum dots could be used in blue-green lasers or flat-panel displays.

"The present work hence opens the door for comprehensive, nondestructive and quantitative 3-D imaging of a wide range of samples including porous materials, semiconductors, quantum dots and wires, inorganic nanostructures, granular materials, biomaterials, and cellular structure," they wrote in the article.