The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy
Leo 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.
2 Debye Institute for Nanomaterials Science, Utrecht University, Post Office Box 80000, 3508 TA Utrecht, Netherlands.
* To whom correspondence should be addressed. E-mail: lgr{at}zurich.ibm.com
