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Chemical Imaging Group Research:

Ultrafast and Chemically-Specific Microscopy for Atomic-Scale Imaging of Nano-Photocatalysis

Our efforts in this new initiative involve developing and applying novel techniques to substantially enhance our ability to understand atomic-scale mechanisms of photocatalytic reactions through experiments combining spectroscopic chemical specificity, sub-nanometer spatial resolution, and sub-picosecond temporal resolution. These techniques will be applied to study of the dynamics of photoinduced chemical transformations at nanostructured surfaces. We are currently pursuing two related avenues: (i) electron induced surface and adsorbate manipulation and chemistry and (ii) time-resolved scanning-tunneling microscopy. The multidimensional approach underlying this work represents a new way of imaging surface chemical reactions and their relation to ultrafast carrier dynamics.

Initial experiments involving atomic manipulation and spatially-resolved chemistry have been focused on model photocatalytic systems and are based on the unique capability of the STM to deliver a highly spatially-localized electron flux to the surface to induce diffusion and desorption.

Work in the area of time-resolved STM has involved combining ultrafast laser excitation with STM detection and imaging to resolve photochemical surface events and electron dynamics, and relies on spatially-resolved electron detection with the STM in conjunction with pulse correlation methods to provide simultaneous sub-nanometer and sub-picosecond measurement of carrier dynamics.

This program is a joint effort with Peter Sutter (team leader, Interface Science and Catalysis Group) at the Proximal Probes Facility in Brookhaven’s Center for Functional Nanomaterials.


Schematic illustrations of local electronic excitation and local detection of photoexcitation. The image at the left illustrates desorption induced by electronic excitation where pulses of electrons from the STM tip initiate the process at a well-defined point in space. The image at the right shows how light energy deposited into the electron temperature bath of a metal can be locally probed by the STM. Excitation with an ultrafast laser pulse initiates the process at a well-defined point in time. In both cases we are investigating the central role that electrons play in surface photochemistry.

 

 

 Last update on: February 03, 2009