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Overview

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 chemistry.

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.

 Research Programs

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).

Chemical Physics:
“Clocking” Heterogeneous Catalysis

Our work in this area addresses ultrafast investigations of surface chemical dynamics as part of a larger program in Surface Chemical Dynamics. 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. …more »

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 transfer timescales.

This research is a component of the Chemical Physics program in the Chemistry Department at Brookhaven and involves collaborations with Mike White (White Surface Dynamics Group), Ping Liu (Catalysis on the Nanoscale), and Alex Harris (Ultrafast Surface Dynamics).

Chemical Imaging:
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.
 
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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 Peter Sutter (team leader, Interface Science and Catalysis Group) at the Proximal Probes Facility in Brookhaven’s Center for Functional Nanomaterials.

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 Last update on: March 09, 2009