A Molecule Carrier

We found that anthraquinone diffuses along a straight line across a flat, highly symmetric Cu(111) surface. It can also reversibly attach one or two CO2 molecules as cargo and act as a molecule carrier, thereby transforming the diffusive behavior of the CO2 molecules from isotropic to linear. Density functional theory calculations indicated a substrate-mediated attraction of ∼0.12 electron volt (eV). Scanning tunneling microscopy revealed individual steps of the molecular complex on its diffusion pathway, with increases of ∼0.03 and ∼0.02 eV in the diffusion barrier upon attachment of the first and second CO2 molecule, respectively