Zooming In

August 30, 2009

There are reports at both the BBC News and the New Scientist about an apparent breakthrough in the microscopic imaging of the very small, by scientists at IBM Research in Zürich. (This is the same lab where Gerd Binnig and Heinrich Rohrer invented the scanning tunneling electron microscope in 1981, for which they won the 1986 Nobel Prize in Physics.)  The IBM group has managed, for the first time, to capture an image of an intact organic molecule, pentacene, which consists of five linked benzene rings, showing its structure, even to the positions of the hydrogen atoms on the periphery.  (Both stories have an image of the molecule.  It is about 20 ångstrom  units long, or 2.0 × 10-9 meter.)

Although images on this scale have been produced before, previous techniques have not been able to image molecules, because the imaging itself disrupted the molecular structure.  The team used a modified method of atomic force microscopy, with a single moecule of carbon monoxide ( CO ) at the tip of the probe:

The molecule is very fragile, but the researchers were able to capture the details of the hexagonal carbon rings and deduce the positions of the surrounding hydrogen atoms.

Although van der Waals force attracted the tip to its target, a quantum-mechanical effect called the Pauli exclusion principle pushed back. This happens because electrons in the same quantum state cannot approach each other too closely

When I was studying chemistry and physics in college, we covered the structure of these molecules, and their physical and chemical properties.  Quantum theory told us how things should behave at an atomic and sub-atomic scale, but it wasn’t something we could measure — we thought it was pretty cool that we could measure bond lengths and angles with a microwave spectrometer.

This development could be of significant value in the design of nanotechnology components, and perhaps in the development of drugs, since the function of so many biologically important molecules depends on their shape.

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