STRUCTURE OF A MOLECULE

Science 28 August 2009:Vol. 325. no. 5944, pp. 1110 - 1114DOI: 10.1126/science.1176210
Reports
The Chemical Structure of a Molecule Resolved by Atomic Force MicroscopyLeo Gross,1,* Fabian Mohn,1 Nikolaj Moll,1 Peter Liljeroth,1,2 Gerhard Meyer1
Resolving individual atoms has always been the ultimate goal of surface microscopy. The scanning tunneling microscope images atomic-scale features on surfaces, but resolving single atoms within an adsorbed molecule remains a great challenge because the tunneling current is primarily sensitive to the local electron density of states close to the Fermi level. We demonstrate imaging of molecules with unprecedented atomic resolution by probing the short-range chemical forces with use of noncontact atomic force microscopy. The key step is functionalizing the microscope’s tip apex with suitable, atomically well-defined terminations, such as CO molecules. Our experimental findings are corroborated by ab initio density functional theory calculations. Comparison with theory shows that Pauli repulsion is the source of the atomic resolution, whereas van der Waals and electrostatic forces only add a diffuse attractive background.
1 IBM Research, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland.2 Debye Institute for Nanomaterials Science, Utrecht University, Post Office Box 80000, 3508 TA Utrecht, Netherlands.