FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Materials Science and Technology Division
determining catalytic properties: the energy of the electrons and the electron density at the surface of the
films. Moreover, confinement can induce magnetism in otherwise nonmagnetic metals. We have grown
ruthenium quantum films of different thicknesses. Two different growth modes resulted in interesting
properties for catalysis and nanoengineered magnetism. Accordingly, electronic and magnetic properties
of these films were studied both in situ and ex situ using scanning tunneling microscopy, X-ray
photoemission spectroscopy, and superconducting quantum interference device measurements.
Mission Relevance
The project is directly relevant for the science mission of DOE: we will utilize quantum mechanical
effects to directly control catalytic action, pushing the field forward from catalyst discovery to true
catalyst design—a goal stated in the DOE report Basic Energy Needs—Catalysis for Energy. The project
is also relevant for the Defense Advanced Research Projects Agency (DARPA) since it promises the
design of a nanoscale catalyst for decentralized and on-demand hydrogen production for clean energy.
The DARPA program Surface Catalysis for Energy (DARPA-BAA-08-48) has expressed interest in work
that would follow the proof of principle in this project. We have been successful in obtaining follow-on
funding for continued research in this direction through the DOE Office of Basic Energy Sciences
(ERKCS87).
Results and Accomplishments
Despite initial difficulties to grow quantum stabilized films, two surprising discoveries were made. Due to
an unexpected growth mode of ruthenium on silicon, the project has split into two directions and the stage
of water splitting has not yet been reached. Nevertheless, both directions have progressed well. First,
ruthenium deposition on silicon unexpectedly resulted in the growth of ruthenium nanocrystals with a
very narrow size distribution. While ruthenium in bulk form is paramagnetic, we have surprising evidence
that these ruthenium nanocrystals are (weakly) ferromagnetic, potentially opening new avenues towards
nanoengineered magnetic materials. The second direction was started in order to obtain atomically flat
films of ruthenium (instead of the nanocrystals that were obtained on silicon substrates) for controlled
catalytic water splitting experiments. We are using a nearly lattice matched palladium substrate in this
direction of research. Our results suggest that quantum stabilized ruthenium thin film growth can be
obtained. These are the first transition metal quantum films ever realized. Against expectations, this
growth mode only appeared after a high temperature annealing step. This contrasts with all other known
quantum stabilized film growth that only survives (far) below room temperature. High temperature access
to quantum mechanically tunable nanoscale metal films bears great promise not only for academic model
systems but, more importantly, for real industrial applications. Currently, we are performing further
experiments to conclusively establish ferromagnetism in the nanocrystals to reach publication stage, and
we are optimizing the flat quantum film growth to study water splitting in well-defined samples.
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