[Under construction]2014 AFOSR MURIShedding light on plasmon-based photochemical and photophysical processesPO: Dr. Michael Berman, Molecular Dynamics and Theoretical Chemistry PI: Dr. Nancy Halas, Rice UniversityWebsite: TBD
The proposed MURI will advance our fundamental understanding of heterogeneous photocatalysis, a topic at the junction of chemistry, physics, and photonics engineering, which is currently poorly understood. The efficient coupling of light energy to drive otherwise thermodynamically unfavorable chemical reactions is of particular interest to the DoD for energy and sustainability-related applications leading to new, asymmetric technologies. For example, the direct use of sunlight to create clean fuels or to remediate dangerous biological or chemical agents would be truly revolutionary. Plasmon-induced processes have been shown to drive chemical reactions, primarily through generation of hot carriers in the metal which transfer to adsorbate molecules, lowering reaction barriers. Optical excitation of plasmons also leads to the generation of intense local electromagnetic fields known as “hot spots”, and strong photothermal effects. The latter process have recently been shown (by our team members) to give rise to plasmon-induced solar steam generation at an efficiency of over 80%.
The proposed MURI team brings together experts in plasmonics and nanoscale and ultrafast spectroscopies to study the fundamental mechanisms of plasmon-induced photochemical and photophysical processes. Team members are: Louis Brus (Columbia U.), Emily Carter (Princeton), Renee Frontiera (U. Minnesota), Peter Nordlander, Stephan Link, Junrong Zheng, and Naomi Halas (PI) (Rice U.). Also included on our team is Christoph Lienau from the University of Oldenburg, Germany (not on budget). Theorists in the areas of first-principles quantum theory of adsorbate-surface interactions (Carter) and quantum plasmonics (Nordlander) will interact directly with experts in plasmon-enhanced chemical processes and photocatalysis (Brus), plasmonic nanostructure design/synthesis/fabrication and –enhanced spectroscopies (Halas), and optical spectroscopies. These include single-nanoparticle methods (Link), 2D UV-Vis-IR (Zheng), time-resolved and fsec stimulated surface-enhanced Raman scattering (Frontiera) and time-resolved photoemission with 10 fsec time resolution (Lienau). Our MURI team’s focus will be on designing and developing plasmonic substrates as efficient hot electron/hole sources. The charge transfer process from photoexcited surface plasmons to adsorbate molecules will be studied using these substrates and model molecular systems. Studies will include four chemical reactions: (a) light-driven dissociation of diatomic molecules at surfaces, (b) the hot hole-driven photo-oxidation and electron transfer growth of nanoparticles; (c) photocatalytic water splitting, and (d) the photoreduction of CO2, critical for the solar-based production of liquid fuels. This full range of experimental capabilities will be used to study plasmon-induced liquid-vapor phase transitions. The anticipated outcome of this research will be a significant advance in our fundamental understanding of plasmon-induced chemical and physical processes, successful strategies for developing useful plasmonic substrates that drive these processes, and a knowledge base that will enable the study of plasmon-induced processes as a major new frontier in physical chemistry research.