Sizing Up Atoms with Electron Holograms

Article excerpt

In their ongoing quest to see the all-but-invisible, physicists have developed a method for using patterns of scattered electrons to observe the three-dimensional atomic textures of materials. In this emerging technology, called electron holography, investigators exploit the wave-like properties of electrons to make their observations (SN: 10/15/88, p.252).

Now scientists have used a lensless electron projector to discern the arrangement of atoms in several types of materials. In the Sept. 16 PHYSICAL REVIEW LETTERS, Hans-Werner Fink and Heinz Schmid of IBM's Zurich (Switzerland) Research Laboratory and their colleagues describe the technique and the calculations that helped them create holograms of carbon fibers and of thin gold films. Since doing that work, they have produced a holographic image of DNA--published here for the first time--demonstrating that the approach also works with biological materials.

Fink and Schmid illuminate their samples with a beam of electrons emitted from an ultrathin tungsten tip similar to that used in scanning tunneling microscopy. By sharpening this tip to a width of one atom, they create a beam coherent enough to make atomic-scale holograms.

"Holograms are not direct pictures of objects; they are sort of smeared-out representations," explains Hans Jurgen Kreuzer, a physicist at Dalhousie University in Halifax, Nova Scotia. He and Dalhousie colleague Andrzej Wierzbicki worked with the IBM scientists to make a model for predicting the scattering patterns and to interpret experimetnal results. "We now have a theory that eliminates the guesswork," Kruezer says.

But these researchers and others agree that the images still need work. …