Controlling the Electronic Structure of Metallic Nanoparticles using Surface Chemistry

With support from the Macromolecular, Supramolecular and Nanochemistry Program (MSN) in the Division of Chemistry, Benjamin Lear of Pennsylvania State University is combining surface chemical synthesis and advanced chemical analysis tools to study how the electronic properties of metal nanoparticles are altered by molecules at their surfaces. Metal nanoparticles provide unique electronic properties that form the basis of new medical treatments, manufacture of high value chemicals, and energy conversion processes. However, there are currently limited means by which to control the underlying electronic properties and, thereby, control the efficiency and power of their use. The Lear research team is working to develop new chemical means to control and tune these electronic properties, utilizing the molecules often present at the surface of these particles. They focus on controlling the number of ways that electrons can be held on the metal. This fundamental property underpins familiar behaviors like electrical conduction, thermal conduction, and luster. Measuring the magnetic behavior of metal nanoparticles provides quantitative insight into this fundamental property. In addition to the technical impacts expected from this work, Dr. Lear and his students will be creating a website that provides clear design rules for communication through visualization of data. Because the preponderance of scientific communication relies on such visualizations, increasing the effectiveness and clarity of presentation will benefit fellow scientists, policy makers, and the general public. Under this award, the research team led by Benjamin Lear at Pennsylvania State University seeks to develop a framework for ligand control over the electronic structure of metallic nanoparticles. The underlying hypothesis is that the nature of the ligand-metal interface influences the position of the Fermi energy of the metal as well as the density of states at the Fermi energy. These properties are extracted from measurements of the Pauli paramagnetism of the particles and electron paramagnetic resonance (EPR) spectra. The team specifically seeks to understand how the influence of the ligands changes with binding mode, composition of the ligand layer, and size of the metallic nanoparticles. The team also seeks to understand the nature of the coupling between metallic electronic states and ligand electronic states, using pulse EPR. By systematically varying the ligands at nanoparticle surfaces, and measuring accompanying changes in magnetic properties, the Lear group is developing a framework that could enable other scientists and engineers to rationally control the behaviors of metal nanoparticles, increasing their utility. 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.