CaSTL Seminar with Phillip Christopher

Date: 
Thursday, April 16, 2015 - 01:00
Location: 
2201 Natural Sciences II
Speakers: 
Phillip Christopher, UC Riverside
Event Title: 
Unique properties of photon-assisted catalysis at metal nanocrystal surfaces
Host: 
Eric Potma

Photon driven chemical reactions at metal surfaces have been studied for over forty years with a focus on non-adiabatic, electron driven chemical processes in the context of controlling reaction selectivity. A majority of these studies have been executed on metal single crystals, where surface electric fields have small magnitudes and chemistry is typically driven through substrate-mediated excitation of adsorbate-metal bonds that competes with hot charge carrier diffusion into the bulk. These characteristics result in catalytic processes with characteristically low yields and minimal, if any, ability to control the outcome of probed chemistry as the processes of photon absorption and induced chemical reactions are delocalized from each other.

 

Metal nanocrystals offer opportunities to overcome these limitations through the enhanced electric fields created in response to excitation of localized surface plasmon resonance and exploiting huge surface area to volume ratios that allows chemistry by direct photoexcitation of adsorbate-metal bonds. In this talk I will discuss recent results where we show that decaying plasmonic excitations at junctions of Ag nanocrystals can be efficiently funneled into catalyzing O2 dissociation on the Ag surface. Associated with plasmon driven chemical reactivity are unique wavelength, intensity and isotope dependencies, which shed light on fundamental mechanistic insights. In a second example, I will describe how the large surface area to volume ratio characteristic of sub 5 nanometer diameter metal crystals can be exploited to control outcome of catalytic processes through direct photoexcitation of targeted adsorbate metal-bonds. The implications of these results and unresolved questions will be discussed.