Taeyoung Choi

A Single Molecule Kondo Switch: Multistability of Tetracyanoethylene on Cu(111)

Single tetracyanoethyelene (TCNE) molecules on Cu(111) are reversibly switched among five states by applying voltage pulses with the tip of a scanning tunneling microscope. A pronounced Kondo resonance in tunneling spectroscopy indicates that one of the states is magnetic. Side bands of the Kondo resonance appear at energies which correspond to inter- and intramolecular vibrational modes. Density functional theory suggests that molecular deformation changes the occupancy in TCNEs molecular orbitals, thus producing the magnetic state.

Building blocks for studies of nanoscale magnetism: adsorbates on ultrathin insulating Cu2N

Scanning tunneling microscopy and spectroscopy were performed to study transition metal adatoms (Fe, Co, Cu) and individual metal-dithiol complexes on insulating Cu2N islands. Adsorption of metal adatoms on Cu2N is surprisingly complex and in the case of Fe, we find two distinct adsorption states for each of two distinct adsorption sites. Connection of these metal adatoms to dithiol molecules was pursued to model a single molecule junction, with the aim of understanding further details about the nature of metal/molecule electrical contact. Pronounced changes in local density of states, magnetic anisotropy and Kondo interactions were observed for Co adatoms connected to dithiol molecules. These results illustrate some of the challenges and opportunities for STM studies of nanoscale magnetism in complex systems.