title: Bond-order discrimination by atomic force microscopy.
abstract: We show that the different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes can be distinguished by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)-functionalized tip. We found two different contrast mechanisms, which were corroborated by density functional theory calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images decreased with increasing bond order because of tilting of the CO molecule at the tip apex.
authors.affiliation: IBM Research-Zurich, CH-8803 Rüschlikon, Switzerland. lgr@zurich.ibm.com
authors.forename: Leo
authors.initials: L
authors.lastname: Gross
authors.forename: Fabian
authors.initials: F
authors.lastname: Mohn
authors.forename: Nikolaj
authors.initials: N
authors.lastname: Moll
authors.forename: Bruno
authors.initials: B
authors.lastname: Schuler
authors.forename: Alejandro
authors.initials: A
authors.lastname: Criado
authors.forename: Enrique
authors.initials: E
authors.lastname: Guitián
authors.forename: Diego
authors.initials: D
authors.lastname: Peña
authors.forename: André
authors.initials: A
authors.lastname: Gourdon
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meyer
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D004583:Electrons; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons; D011083:Polycyclic Compounds; D012965:Sodium Chloride; D003300:Copper; D002248:Carbon Monoxide; C012256:coronene