| AVS 59th Annual International Symposium and Exhibition | |
| Scanning Probe Microscopy Focus Topic | Tuesday Sessions |
| Session SP+AS+BI+ET+MI+NS-TuA |
| Session: | Advances in Scanning Probe Imaging |
| Presenter: | J. Lee, University of California, Irvine |
| Authors: | J. Lee, University of California, Irvine S.M. Perdue, University of California, Irvine A. Rodriguez Perez, University of California, Irvine P.Z. El-Khoury, University of California, Irvine V.A. Apkarian, University of California, Irvine |
| Correspondent: | Click to Email |
Taking advantage of both elastic and inelastic tunneling processes of a molecule isolated at the double-barrier tunneling junction of a scanning tunneling microscope, both static and dynamic parts of the Hamiltonian can be visualized with submolecular resolution. This is illustrated by imaging Jahn-Teller (JT) driven vibronic dynamics within Zn-etioporphyrin (ZnEtio), in its various reduced forms, in what may be regarded as nature’s choice of a molecule as a controllable current switch. Unique interpretations are afforded through simultaneously recorded functional images, such as maps of: a) energy resolved differential current, b) spectrally resolved electroluminescence, c) conduction bistability, d) reduction/oxidation potentials (maps of charging and discharging). We focus on the radical anion, ZnEtio-, which is reduced by injecting an electron to a single ZnEtio molecule adsorbed on a thin aluminum oxide film grown on NiAl(110). In contrast with the neutral, the saddle-shaped radical anion lies flat on the surface of the oxide. The discharge map directly shows that the excess electron is localized in the 2px orbital of the entire porphyrin macrocycle, as a result of the JT active rectangular (B1g) distortion of the molecule. The static JT potential leads to conduction bistability, with reversed switching polarity depending on whether tunneling electrons are injected in the occupied 2px orbital or the diamond (B2g) coordinate which serves as a transition state that connects the px and py orbitals at the two B1g minima. In addition to the JT switching, the dynamic JT states are directly imaged through electroluminescence spectra, induced by injection of a second electron in the anion. The spectra consist of a continuum due to radiative ionization of the dianion, and sharp Fano resonances of the vibronic progression of the JT active modes. A detailed analysis of the spectra yields the vibronic couplings and the wavefunctions. Vibronic structure is inherent in STM topographic images, and has hitherto not been fully recognized.