Single Molecule Imaging, Spectroscopy, Dynamics, and Chemistry

   Our research focuses on nanoscale chemical and physical phenomena with an emphasis on probing the basic properties of single atoms and molecules in their nano-environment on solid surfaces. The goal is to obtain detailed descriptions of single atoms and molecules which form the basis for understanding chemical and physical processes at surfaces and properties of nanostructured condensed matter and molecular materials.

    The understanding of matter and its interactions with the surrounding at the atomic and molecular level is the central theme of our research program. The ability to control chemistry at the level of individual atoms and molecules underpins the way they interact and use the available energy to affect chemical transformation. The study of magnetism down to single atoms allows the understanding of how the electron spins play a role in chemical and physical processes.

    The scanning tunneling microscope (STM) is a tool which not only allows us literally to see individual atoms and molecules but also to manipulate and spectroscopically characterize them. It is an all-purpose tool and is in effect a nanoreactor carrying out reactions with atoms and molecules in the nanocavity of the tunnel junction. Since the coupling of electrons to the nuclear motions provides the driving force for chemical transformation, the STM with its tunneling electrons can be tuned to induce atomic and molecular motions and to dissociate and form chemical bonds.

    Tunneling electrons can be spin polarized. The STM can be used to probe magnetism and the effect of magnetic impurity on superconductivity and other solid state phenomena associated with the electron spin.

We have demonstrated that chemical analysis with the STM is possible with inelastic electron tunneling spectroscopy (IETS) and have reached the limit of sensitivity of vibrational spectroscopy, that of a single bond. The ability to measure spatially resolved vibrational intensity with sub-Angstrom resolution in single molecules makes it possible to directly determine quantitatively a number of fundamentally important physical and chemical processes.

    The STM can be used effectively to probe solid state and molecular materials at the spatial limit. Its versatility is reflected in a wide range of problems which have been successfully investigated. These include intramolecular energy transfer, energy dissipation resulting from bond breaking, chemical identification and structural determination of reactants and products involved in the making of individual chemical bonds and intermediates in multistep reactions, the coupling of electrons to nuclear motions via individual molecular orbitals (orbital-specific chemistry), electrical conductivity through single molecules (molecular electronics), classical and quantum diffusion (tunneling) of single hydrogen atoms, the spatially dependent interactions between two molecules, and the fundamental motions of molecules (rotation, vibration, translation).

Last Updated: May 8, 2013