In Pixar's Inside Out, Joy proclaims, "Do you ever look at someone and wonder, what's going on inside?" My group asks the same question about nanomaterials whose function plays a critical role in energy, biology, and information-relevant processes. In this presentation, I will describe new techniques that enable visualization of nanoparticle phase transitions and light-matter interactions with nanometer-scale resolution. First, we explore nanomaterial phase transitions induced by solute intercalation, to understand and improve materials for energy storage applications. As a model system, we investigate hydrogen absorption and desorption in individual palladium nanocrystals. Our approach is based on in-situ electron energy-loss spectroscopy in an environmental transmission electron microscope. By probing hydrogen-induced shifts of the palladium plasmon resonance, we find that sub-30nm single-crystalline nanoparticles do not exhibit phase-coexistence and that surface effects dictate the size dependence of the hydrogen absorption pressures. Then, we introduce a novel tomographic technique, cathodoluminescence spectroscopic tomography, to probe optical properties in three dimensions with nanometer-scale spatial and spectral resolution. Particular attention is given to reconstructing a 3D metamaterial resonator supporting broadband electric and magnetic resonances at optical frequencies. Our tomograms allow us to locate regions of efficient cathodoluminescence across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. This tomographic technique could be used to precisely locate radiative recombination centers in light-emitting diodes, to probe the nanoscale distribution of defect states in organic photovoltaics, and potentially to provide new label-free avenues for biological imaging. Taken together, our results provide a general framework for high-resolution visualization of chemical reactions and light-matter interactions, well-below the diffraction limit and in three-dimensions.
Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.
Refreshments in the lobby of Varian Physics at 4:15 pm.
Autumn 2015/2016, Committee: A, Linde (Chair), S. Chu, P. Hayden, M. Schnitzer, L. Senatore