C60 molecules show atom-like states Characterization

May 30, 2008

Calculation of a delocalized atom-like orbital on a one-dimensional wire of C60 molecules. (Courtesy of Jin Zhao.)

Atom-like molecular electronic orbitals can be found bound to the hollow core of buckminsterfullerene (C60) cages in addition to the molecular orbitals present in the carbon framework, say researchers from the University of Pittsburgh and the Donostia International Physics Center in Spain [Feng et al., Science (2008) 320, 359].

The ‘superatom molecular orbitals’ (SAMOs), as they have been named by the team, bring to mind the spherical s, p, and d symmetries of atomic orbitals. “Such orbitals should be a common feature of hollow molecules such as C60, carbon nanotubes, and others derived by wrapping or rolling of molecular sheets”, says Hrvoje Petek of the University of Pittsburgh.

The team used scanning tunneling microscopy (STM) and density functional theory calculations to study the electronic structure of single C60 molecules, one-dimensional C60 quantum wires, and two-dimensional C60 assemblies. At low temperatures and using a STM bias greater than 3.5 V, a transition from a π molecular orbital to nearly free-electron (NFE)-like character can be observed in these molecules.

“Our research shows that hollow molecules with atom-like orbitals can achieve sufficient wave function overlap for electrons to delocalize over a molecular assembly as would free electrons in metals,” adds Petek. “If this could happen close to the Fermi level, such molecules could conduct like metals.”

The team will investigate how specific modifications of C60 molecules lower the energy of superatom orbitals, in order to bring them within the reach of practical applications, explains Petek.

Katerina Busuttil