Researchers at the Elettra synchrotron facility, ICTP's 'light source' partner in Trieste, have recently discovered a holographic technique for deciphering the structure of atoms.

Atomic Holograms

Alberto Morgante

Atoms may be small, but understanding their structure is no small matter. In fact, since the time of the famed physicist and Nobel Prize winner Ernest Rutherford in the early twentieth century, scientists have sought to discern the structure or arrangement of atoms in molecules, crystals and all sorts of biological, chemical and physical configurations.
How have they sought to accomplish this task? Relying on a variety of tools, including spectroscopic microscopes, X-rays and synchrotron light sources, they have literally bounced stuff off atoms in tiny 'pinball-game-like' environments to produce a scattering process that ultimately projects a discernible pattern. The problem has been that the pattern could only be interpreted through time-consuming calculations. To simplify and speed up the time for analysis, scientists have sought to apply algorithms to generate an immediate image of the atoms. This process is called 'inversion.'
Now a group of researchers that includes Italian physicist Alberto Morgante, who oversees the Aloisa beamline at the Elettra Synchrotron Light Source in Trieste, has taken the inversion process a significant step forward by successfully marrying electron scattering techniques to photoelectronic holography to create 'strikingly beautiful' three-dimensional images of the local arrangement of atoms. Morgante's work was conducted jointly with a group of researchers at the University of Zurich in Switzerland.
There is good reason why this breakthrough technique, which has been labelled "internal source holography," recently received extensive press coverage in Nature, Physical Review Letters, and Europhysics News. Previously, researchers were forced to devise complex mathematical models to project the possible arrangement of atoms. As Morgante explains it, "the analytical process was a difficult one, requiring trial-and-error procedures that were not only terribly time-consuming but often ended in failure. After all," Morgante observes, "modelling researchers were literally working in the dark since there was no way to confirm the models' predictive power through experimentation and observation."
"Internal source holography," Morgante says, "sheds light on the structure of atoms in ways that give researchers a reasonable fix on atomic arrangements without expending a great deal of time or engaging in a great deal of guess work. In fact, for simple molecules and crystals, the arrangement can be discerned through a few straightforward mathematical calculations no more difficult than multiplication or division."
As a result, while data collection remains a tedious task, the analytical process has become much faster and more reliable. For this reason, Morgante and his colleagues are anticipating that photoelectron holography will prove an invaluable tool in a broad range of fields, including biology (in the study of molecules), chemistry (in the examination of catalysts), and physics (in research on nanostructures).
Internal source holography, notes Morgante, "will reveal the structure of small atomic clusters that cannot be crystallised for analysis by conventional X-ray crystallography." The result is a more precise picture of our atomic world that is likely to reveal expanded pathways of understanding in a variety of scientific fields.

For more detailed information about photoelectron holography, see "Hologram of Atoms," Nature 410 (26 April 2001), pp. 1038-1039; "Imaging Atom Sites with Near Node Photoelectron Holography," Europhysics News 32/5 (September/October 2001), pp. 172-175; and "Atomically Resolved Images from Near Node Photoelectronic Holography Experiments on A1(111)," Physical Review Letters 11 (12 March 2001), pp. 2337-2340.

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