Credit: © 2009 AAAS

Traditionally, chemists have used indirect spectroscopic methods to understand the structure of single molecules; making inferences from techniques such as infrared and NMR spectroscopy. The advent of new microscopy techniques, however, has allowed a more direct visualization of such structures.

Non-contact atomic force microscopy (NC-AFM) works by scanning a surface with an oscillating tip that, without making physical contact, interacts with different surface features, which induce variations in the oscillating frequency. These can be measured and an image of the scanned area created. This technique, however, has failed to achieve the resolution required to image an individual molecule and differentiate all atoms. Now, a team led by Leo Gross from IBM research in Zurich has imaged1 all of the atoms in pentacene on either a conducting or non-conducting surface — remarkably even including the C–H bonds.

The improved resolution was achieved by functionalizing the AFM tip with an adsorbed molecule of carbon monoxide. This modifies the interactions between the surface and the tip and allows it to get closer to the molecule without disturbing it. This enables high-resolution imaging as the tip can then get close enough to 'feel' (Pauli) repulsive forces associated with regions of high electron density overlap, such as where the pentacene atoms and bonds appear.