Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

DYNAMIC STUDIES OF PHOTO- AND ELECTRON-INDUCED REACTIONS
ON NANOSTRUCTURED SURFACES
Richard Osgood, Center for Integrated Science and Engineering, Columbia University,
New York, NY 10027, Osgood@columbia.edu
Program Scope or Definition:
Our current research program examines the photon- and electron-initiated reaction
mechanisms, half-collision dynamics, and other nonequilibrium-excited dynamics effects,
occurring with excitation of adsorbates on well-characterized metal-oxide and
nanocrystal surfaces. In order to explore these dynamics, we have first developed new
synthesis methods for uncapped nanocrystals with specific reconstructions and orientation
in a UHV STM instrument. We have used tunneling from the tip of our STM ( and
will use an in situ flood UV lamp) to excite adsorbate molecules at specific sites of these
nanocrystals. The resulting chemistry and surface dynamics are then investigated via imaging
of reaction fragments in the vicinity of the reaction sites. Additional research tools
are time-of-flight detection, XPS, standard UHV probes, in situ TPD, and molecular
computational tools. Our initial experiments have been directed toward electronictunneling
reactions in a series of linear aromatics on rutile TiO2(110) surfaces, as well as
the determination of the conditions needed to form uncapped TiO2 nanocrystals with a
known atomic structure. Our adsorbate molecules have been chosen to have sufficient
binding energy to examine reactions at temperatures of > 100K.
From the perspective of DOE energy needs, photoexcitation is of continuing interest
for its importance in photocatalytic destruction of environmental pollutants, in several
methods of solar-energy conversion, and in a variety of applications of nanotechnology.
Our recent work in this program has yielded several new research findings regarding
the preparation of nanocrystals and their reactive properties, the structure of adsorbed aromatics
on TiO2 surfaces, and the observation of tip-induced-electron bond cleavage
within these molecules.
Recent Progress:
The methodology of our research program is to progress from measurements on a planar
single-crystal sample of TiO2(110) surface to comparable experiments on a nanocrystal
surface. The nanocrystals are prepared using surface-alloy growth, which is a synthesis
method pioneered in our group; thus characterization of this method forms an important
component of our research. In our talk here, we will focus on
both the nanocrystals, thermal-induced reactions and molecular
orientation, and on our recent research on tip induced reactions
of adsorbate molecules on a single-crystal TiO2 surface. Our
central tool for this research is our instrumented STM system.
Adsorption Geometry of Reaction Target Molecules on a Reconstructed
Surface: Planar Aromatics on Single-Crystal, Ru-
Fig. 1: 5 nm × 5 nm
STM image of 4bromobiphen-yl-exposed
TiO2 (110) surface at
T=300K. Bright ellipselike
features are due to Ti
sites in TiO 2 substrate.
tile TiO2(110)
Molecular orientation plays a key role in many surface or interfacial
applications involving self-assembly, catalysis, and
charge transfer. STM in conjunction with a pristine surface is a
powerful tool that allows direct observation of the geometric
orientation of adsorbed molecules and hence can further our
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