Revealing the Angular Symmetry of Chemical Bonds by Atomic Force Microscopy

• Published in: Science (American Association for the Advancement of Science) Vol. 336; no. 6080; pp. 444 - 449
• Main Authors: Welker, Joachim, Giessibl, Franz J.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 27.04.2012; The American Association for the Advancement of Science
• Subjects: Adatoms; Atomic and molecular collision processes and interactions; Atomic and molecular physics; Atomic force microscopes; Atomic force microscopy; Atomic interactions; Atoms; Atoms & subatomic particles; Bonding; Carbon monoxide; Chemical bonding; Chemical bonds; Chemistry; Copper; Energy; Exact sciences and technology; Flats; Frequency shift; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions; Interatomic potentials and forces; Laboratory Equipment; Mathematical minima; Microscopy; Molecular chemistry; Molecules; Morse potential; Orientation; Physics; Scanning probe microscopes, components and techniques; Scanning tunneling microscopes; Scanning tunneling microscopy; Symmetry; Terminals; Tips; Tunneling; Atomic force microscopy; Force measurement; Microscope tips; Tunnel effect; Interatomic interaction; Scanning tunneling microscopy; Adsorbed state; Tip surface interactions; Chemical bonds; Interaction potentials; Carbon monoxide; Copper; Model potential
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1219850

We have measured the angular dependence of chemical bonding forces between a carbon monoxide molecule that is adsorbed to a copper surface and the terminal atom of the metallic tip of a combined scanning tunneling microscope and atomic force microscope. We provide tomographic maps of force and current as a function of distance that revealed the emergence of strongly directional chemical bonds as tip and sample approach. The force maps show pronounced single, dual, or triple minima depending on the orientation of the tip atom, whereas tunneling current maps showed a single minimum for all three tip conditions. We introduce an angular dependent model for the bonding energy that maps the observed experimental data for all observed orientations and distances.