Collaborative Research: Probing and Controlling Exciton-Plasmon Interaction for Solar Hydrogen Generation

Both semiconductors and metals can be produced in the form of nanoparticles, a size of about 10,000 times smaller than the thickness of a typical human hair. Certain semiconductor nanoparticles, called semiconductor quantum dots, exhibit new properties when the electrons, also called excitons, in the tiny crystals are spatially squeezed and exposed to light.

Similarly, when a group of electrons in a small metal nanoparticle are confined in space and subject to light, hot electrons, called plasmons, are generated in these metal nanostructures that exhibit novel characteristics. Interaction between excitons in semiconductor quantum dots and plasmons in metal nanostructures are expected to result in new fundamental phenomenon and to be useful for many emerging technologies.

In this collaborative project, PI Jin Z. Zhang from the University of California Santa Cruz and PI Shengli Zou from the University of Central Florida will study semiconductor quantum dots-plasmonic metal nanostructures with controlled electronic interactions as a new class of hybrid nanomaterials called semiconductor-metal heterojunctions. Unlike traditional semiconductor or metal materials, these heterojunctions give rise to unusual properties and novel functionalities.

Working with their students, PIs Zhang and Zou will develop ways to create new semiconductor-metal nano-heterojunctions where the electrons communicate in a controlled manner by linking molecules. This project can have significant impacts on applications ranging from nano-photonics to environment and energy, for example advancing renewable solar fuel generation.

This project will also provide opportunities for training future scientists and engineers in advanced experimental and computational techniques. Through their “open lab” focusing on “Solar Hydrogen from Seawater” each summer, local high school students and teachers will be introduced to the research of this project to enhance public awareness about science.

This collaborative research team will develop novel semiconductor-metal nano heterojunctions to investigate the fundamental interactions between exciton generated on semiconductor quantum dots and plasmon produced in plasmonic metal nanostructures, named “plexciton” from a dynamic perspective using ultrafast laser spectroscopy. This research is motivated by the need to address the challenge that electronic coupling between semiconductor quantum dots and plasmons in plasmonic metal nanostructures is not well understood, hindering device applications in emerging technologies based on semiconductor-metal heterojunctions involving light illumination.

The project involves the systematic study of fundamental factors, such as size, shape, and surface of both the semiconductor quantum dots and plasmons in plasmonic metal nanostructures, which determine the electronic coupling between the semiconductor quantum dots and plasmons in plasmonic metal nanostructures. This will be accomplished by developing designer linker molecules that control and enhance the coupling between them.

The electronic coupling between semiconductor quantum dots and plasmons in plasmonic metal nanostructures will be characterized using a combination of time-resolved photoluminescence, transmission electron microscopy, infrared spectroscopy, nuclear magnetic resonance, electrochemistry, Raman spectroscopy, and ultrafast pump-probe laser spectroscopy methods. Unique conductive or aromatic ligand molecules will be used to both stabilize the semiconductor quantum dots and plasmons in plasmonic metal nanostructures and alter and enhance their electronic coupling so that synergistic effects are achieved between the two nanostructures for photonics applications including light energy conversion into electricity or chemical fuel such as hydrogen.

Computational studies will explore the semiconductor quantum dots-plasmons in plasmonic metal nanostructures interaction and guide and corroborate experimental studies. The project will also provide opportunities for training future scientists in advanced experimental and computational techniques. Through their “open lab” which focuses on “Solar Hydrogen from Seawater” each summer they will introduce the research of this project to local high school students and teachers to enhance public awareness about science.

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.