Chemical Dynamics at Surfaces
Our research is aimed at understanding the physics that drives chemical
processes at the gas-solid interface. Our work is motivated by a desire
to develop a fundamental understanding of surface reactions dynamics
that is relevant to the rational design of future catalytic and
photocatalytic materials. Toward this end we are working to address the
challenge of understanding reaction mechanisms, transition states,
molecular interactions, and energy transfer timescales that determine
the efficiency, selectivity and structure-function relationships in
Surface chemical processes, such as the oxidation of CO pictured in this
cartoon, can be driven by energy transfer from the surface to adsorbed
atoms and molecules. Among the factors that determine the reactivity is
the efficiency of the surface–adsorbate energy coupling into the
reaction coordinate. Electrons can play a dominant role in the energy
transfer process. In such cases, the energy coupling will depend
sensitively on the overlap of the molecular and surface density of
states, which is in turn dependent on the physical and electronic and
structure of the substrate–adsorbate complex. We are investigating these
relationships at “molecularly-relevant” time and length scales.
In particular, we are developing existing time-resolved ultrafast-laser
methods for the investigation of model catalytic systems, and we are
exploring new methods to temporally and spatially resolve surface
chemical transformations at “molecularly relevant” time and length
scales, i.e., with sub-picosecond and sub-nanometer precision.
Our research targets model systems relevant to energy-related catalysis
and photocatalysis, including single crystal metals, oxides, and metal
nanoparticles on oxide supports.
We are currently investigating dynamical chemical processes in two
distinct programs: (i) Chemical Physics, where our focus is on
molecule–surface energy transfer dynamics and using photoinitiated
diabatic processes to “clock” surface chemical reactions and
(ii) Chemical Imaging, where our focus is on combining ultrafast laser
pumping with scanning tunneling microscopy (STM) to develop and apply
new approaches to probing electron and molecular dynamics relevant to
nanophotocatalysis. In the former, ultrafast light pulses are used to
deposit energy into the electron temperature bath of a metal to initiate
chemical reactions at a well-defined point in time. In the later, the
STM probe tip is used as an electron source or detector to initiate
chemistry or follow the time evolution of photoexcited electrons with
sub-nanometer spatial resolution. In all cases the common thread is the
key role that electrons play in transferring energy to the adsorbate(s).
“Clocking” Heterogeneous Catalysis
Our work in this area addresses ultrafast investigations of surface
chemical dynamics as part of a larger program in
The overall goal of our component of this larger program is to establish
links between vibrational, electronic and charge transfer dynamics and
the chemistry at the molecule–surface interface.
The adjacent cartoon illustrates a time-resolved “pump–probe” experiment
where we employ ultrafast pulses of light to drive chemistry on model
catalytic surfaces to investigate reaction mechanisms and probe energy
This research is a component of the Chemical Physics program in the
Chemistry Department at Brookhaven and involves collaborations with
Surface Dynamics Group),
on the Nanoscale),
Temporally and Spatially-Resolved Nanophotocatalysis
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.
The adjacent cartoon illustrates a proposed method for subpicosecond
time-resolved scanning tunneling microscopy wherein the STM is used as a
local probe of electrons photoexcited by ultrafast laser pulses.
This program is a joint effort with
Interface Science and Catalysis Group)
for Functional Nanomaterials.