Systematic Study of Plasmon-Induced Charge and Energy Transfer in Metal-Semiconductor Hybrids

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Nontechnical DescriptionThe interaction between light and matter is fundamental to numerous processes in nature, technology, and science. The ability to control light/matter interaction by targeted design of materials and devices is an important part of basic materials science research. Metal nanoparticles possess optical properties that are distinct from their bulk behavior due to the formation of plasmons, the collective excitations of the electron cloud inside a nanoparticle. Plasmons can be very strong light absorbers and their optical properties can be widely tuned, making them promising targets for a broad range of applications such as light sensors and solar energy conversion. However, it is challenging to extract the energy that is contained in plasmons due to their extremely short life time. This research is studying the mechanisms that govern coupling between plasmons and other excitations in matter by combining carefully designed model systems and ultrafast spectroscopies. This project is strongly interdisciplinary, combining Material Science, Physics, and Chemistry. It offers many opportunities for undergraduate and graduate research across these disciplines. A new higher-level undergraduate course, covering the electronic and optical properties of nanomaterials, is being developed as part of the project. In addition, the PI is developing a new module for the University of Delaware’s K-12 Engineering Initiative that supports teachers in STEM education. The module combines hands-on experiences and lectures focusing on the optical properties of nanomaterials.Technical DescriptionThe goal of the project is to understand under what conditions efficient direct plasmon-induced charge and/or energy transfer can be realized and what parameters govern the underlying processes. The project investigates plasmonic interactions between noble metal nanoparticles with tunable optical properties and semiconductors with adjustable electronic properties by ultrafast spectroscopic techniques. The approach combines model systems that allow systematically changing the parameters that are involved in plasmon-induced energy transfer with ultrafast spectroscopic techniques that can identify the formation, dynamics, and the products of plasmon-induced excitations. Highly ordered, homogeneous, and precisely tunable two-dimensional metal/semiconductor hemispherical nano-heterostructure arrays act as test-beds to identify charge transfer mechanisms. The well characterized model systems are investigated by femtosecond transient absorption spectroscopy in the visible and mid-IR spectral range, by time-domain THz emission spectroscopy, and by time-resolved THz absorption spectroscopy. These ultrafast methods are combined with standard materials characterization techniques to measure and identify dynamics of charge and energy transfer processes as a function of optical and electronic material properties. This project develops a detailed predictive understanding of charge and energy transfer mechanisms, that are necessary for rational design of metal/semiconductor hybrid structures for applications such as solar energy conversion and opto-electronics.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.