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Image: Phys. Rev. Lett. 85, 2749

Seeing the atomic details deep inside solid materials is no easy feat. Scanning probe microscopy (SPM) resolves only surface features, and transmission electron microscopy is limited to samples readily traversed by electrons. But Robert Magerle of the University of Bayreuth in Germany has found a way to best both of those approaches. His "nanotomography" method turns a scanning probe microscope on successive layers of a material to build up three-dimensional images of its innards at the nanometer scale. The work appears in today's issue of Physical Review Letters.

For proof of concept, Magerle imaged a synthetic rubber consisting of two polymers, polystyrene and polybutadiene. He first depicted its surface using SPM and then repeated the process 12 times, shaving away a 100 nanometer layer of the sample with a beam of oxygen ions before each step. A computer added up the individual two-dimensional pictures to produce a composite volume image (right). As a bonus, Magerle found, the image offered new structural information about the copolymer, showing exactly how cylinders of its constituents were joined.

Magerle's technique, which lends itself to full automation, should prove especially useful on hard materials, such as metals, crystals, semiconductors and ceramics, and might be able to flesh out defects in transistors that are now missed. "This approach may be quicker, cheaper and more straightforward than competing methods," notes Christopher Harrison of Princeton University. "The combination of SPM and etching techniques should support novel observations, while opening up new avenues for discovery."