In a collaboration with electricalengineers at the Beckman Institute, we are investigating the switchingof energy flow in large molecular structures on surfaces. Theexperiments combine ultra high vacuum scanning tunneling microscopywith both high-resolution and femtosecond laser excitation of thesurface, allowing simultaneous spatial and energy/time resolution.Projects include:

-Laser-assisted desorption of hydrogenatoms to accelerate patterning of hydrogen-passivated silicon surfaces.While an STM tip can remove hydrogen atoms from the surface by breakingthe H-Si bond, this is a very inefficient process that requires as manyas 10^11 electrons scattering off the hydrogen-silicon bond. Bypre-exciting with a laser pulse, the rate of this process may beenhanced.

-Detection of laser absorption onsurfaces by changes in the electron density, a form of single moleculeabsorption spectroscopy. Targets include carbon nanotubes, organicpolymers, and light-emitting proteins.

-Measurements of energy flow andelectron transfer in organic oligomers and dendritic materials. Bybiasing molecules with the STM tip, energy flow can be channeled intodifferent parts of large molecules, effectively turning them into fewnm-sized switches.