Femtosecond Photoinitiated Nanoparticle Surface Chemistry

The goal of this program is to bring together the ultra-fast and the ultra-small in order to understand the physics behind the unique chemistry of nanostructured materials. Towards this end we aim to apply techniques developed to probe the chemical dynamics of 2-D planar surfaces with femtosecond time resolution to the study of the chemistry of molecules adsorbed on supported nanoparticles.

About ten years ago a new class of surface chemical processes was demonstrated and has very recently begun to be exploited to study reaction dynamics on 2-D planar surfaces. These processes involve non-adiabatic excitation driven by the absorption of femtosecond light pulses. However, very little has been done to explore these phenomena on nanoscale materials, where size-dependent properties are expected to impact the dynamics of surface chemical transformations.

There are several aspects of nanoscale systems that we expect to lead to significant changes in their photochemical reactivity and dynamics. We expect spatial confinement of ballistic electrons, size-dependent electronic structure and the sensitivity of electron-phonon coupling to surface thermal vibrations to significantly extend hot electron lifetimes in small nanoparticles. Also, enhancements in photoelectron yield from nanoparticles have been indicated. These effects are expected to dramatically impact photochemical cross sections at nanoparticle surfaces, as well as their dynamics. In particular we aim to explore size-dependent behavior of the photoinduced chemistry and chemical dynamics as the size of the nanoparticles is varied through the size regime spanning the non-metal to metal transition.

The study of photoinduced nanoparticle surface chemistry is important to materials applications in industrial catalysis, atmospheric chemistry, the chemistry of soils and nanofabrication. Because the proposed work addresses femtosecond time scale measurements of electron-mediated chemical transformations on nanoscale surfaces, it intersects with three ongoing efforts at BNL: the Ultrafast Optical Sources Cluster in the Center for Functional Nanomaterials, the Laser-Electron Accelerator Facility, and the Catalysis on the Nanoscale Program. Thus this work nucleates discovery in an important area with the promise of continued growth in a number of different venues at BNL.

This program is supported by a Laboratory-Directed Research and Development Grant (LDRD). We acknowledge Brookhaven National Laboratory for this support.

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Last Modified: June 28, 2012