Characterizing Temperature Gradients Surrounding Plasmonic Nanoheaters and Elucidating their Effects on Chemical Reactions

Professor Stephan Link of the University of Illinois Urbana-Champaign is studying how light absorbed by metal particles a few billions of a meter (nanomoeter) in size is converted into heat. When the particle size is reduced to nanometer dimensions, noble metals have intense colors distinct from their bulk form. These colors are tunable with particle size and shape. Metal particles are therefore explored for their use in various applications that require the transformation of light energy into localized heat, relevant for novel catalysis and advanced manufacturing approaches. However, measuring temperature on the length scale of nanometers is challenging. This research will develop methods to probe temperatures generated by light absorption in a spatially resolved manner, aiming to determine differences between the temperature of the metal particle, its surface, and away from the particle in the surrounding medium. Professor Link will employ complementary thermometry techniques, each sensitive to one of these spatial regions. In addition, Professor Link will participate in programs that educate both college and community college students about nanotechnology to inspire and prepare them to pursue potential careers in science, technology, engineering, and math. Professor Stephan Link of the University of Illinois Urbana-Champaign aims to quantify temperature gradients among core, surface, and surrounding medium in single- to many-particle plasmonic nanoheaters, and to establish their implications in plasmon-assisted photochemical processes. Quantifying temperature at the micro-nanoscale remains a significant obstacle because different thermometry techniques measure temperature in distinct spatial domains: within the nanoheater, at its surface, or in the surrounding medium. Furthermore, while an isolated nanoparticle reaches a constant core temperature that decreases in the surrounding medium inversely with distance, at the many-particle level thermal gradients flatten these temperature profiles due to collective heating effects. This nanoparticle-density dependence of temperature differences among spatial domains must be understood in order to optimize heat-driven physical and chemical processes at the nanoheater surface or in its local surrounding medium. This research addresses the need for characterizing nanoscale temperature profiles through complementary thermometry techniques while varying the nanoparticle density and following a model plasmon-assisted chemical reaction. Translating the knowledge gained from characterizing micro-nanoscale temperature profiles for plasmon-assisted chemical reactions is relevant for the fast-growing field of plasmonic manufacturing. The results generated here have also broad implications for other areas such as quantum information technologies, microelectronics, advanced manufacturing, solar steam generation, and nanomedicine. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.