Chemical Imaging Group Research:
Ultrafast and Chemically-Specific Microscopy for Atomic-Scale Imaging of
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
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
Interface Science and Catalysis Group)
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.