Multi-scale, multi-dimensional imaging of natural and synthetic materials

My research uses correlative, multi-scale approaches, based mainly on electron and light microscopy, to understand how nano- and atomic-scale features affect the bulk optical and electronic properties of crystals.

Plasmonics and Plasmon-Driven Processes

Industries creating inorganic, organic, and agricultural chemicals use a staggering 4.2% of the worldwide delivered energy, mainly from unsustainable fossil fuels. Meanwhile, the sun provides energy that could be utilized to power photochemical reactions sustainably and cleanly. Recent advances revealing how localized surface plasmon resonances (LSPRs), light-driven electron oscillations in metal nanoparticles, can concentrate light at the molecular scale made the dream of efficient photochemistry one step closer. My group works on synthesizing and characterizing new, Earth-abundant plasmonic materials that can trap and concentrate (sun)light directly at a catalytic surface to efficiently and intelligently power and choreograph chemical reactions.

Multiscale Optical/Electron Spectroscopy

A central theme of my current and future research is to use and develop techniques to correlate the optical, compositional, and structural properties of optical materials across length scales in order to unravel structure-function relationships relevant for photocatalysis, plasmonics, sensing, and semiconductors. To this end, we build and utilize optical spectroscopy tools, electron microscopy approaches, and correlative techniques that enable use to interrogate both the optical and structural properties of nanomaterials, from the millimeter to nanometer scale. We also develop specialized sample chambers and markers, enabling the flow of reactive or inert gases and liquids and the easy retrieval of specific areas in subsequent electron microscopy investigation. With such tools, my group routinely correlates the plasmon-induced photon scattering in a variety of single nanoparticles with their size, shape, composition, and local environment; we are also investigating the effect of defects in semiconducting 2D materials (e.g. MoS₂) and of doping in plasmonically active indium tin oxide (ITO).

Localized surface plasmon resonance (LSPR) schematic (left image) shows the coherent oscillation of conduction electrons excited by the light’s electric field. Top right image: Scanning transmission electron micrograph of a Au/Pd NP. Bottom right image: Experimental near-field field map (electron energy loss spectroscopy) of its lowest energy LSPR

• E. R. Hopper, C. Boukouvala, D. N. Johnstone, J. S. Biggins, E. Ringe, “On the Identification of Twinned Body-Centred Cubic Nanoparticles”, Nanoscale (2020), 12, 22009-22013. DOI: 10.1039/D0NR06957D
• E. Ringe, “Shapes, Plasmonic Properties and Reactivity of Magnesium Nanoparticles” Invited Feature Article in J. Phys. Chem. C (2020), 124, 15665-15679. DOI: 10.1021/acs.jpcc.0c03871
• J. Asselin, C. Boukouvala, E. R. Hopper,  Q. M. Ramasse, J. S. Biggins, E. Ringe, “Tents, Chairs, Tacos, Kites and Rods: Shapes and Plasmonic Properties of Singly Twinned Magnesium Nanoparticles” ACS Nano (2020), 14, 5968-5980, DOI: 10.1021/acsnano.0c01427
• J. Asselin, C. Boukouvala, Y. Wu, E. R. Hopper, S. M. Collins, J. S. Biggins, E. Ringe, “Decoration of Plasmonic Mg Nanoparticles by Partial Galvanic Replacement”, J. Chem. Phys. (2019), 151, 244708  DOI: 10.1063/1.5131703
• C. Boukouvala, E. Ringe, “Wulff-Based Approach to Modeling the Plasmonic Response of Single Crystal, Twinned, and Core-Shell Nanoparticles” J. Phys. Chem. C (2019), 123, 25501-25508 DOI: 10.1021/acs.jpcc.9b07584
• J. S. Biggins, S. Yazdi, E. Ringe, “Magnesium Nanoparticle Plasmonics” Nano Lett. (2018) 18, 3752-3758 DOI: 10.1021/acs.nanolett.8b00955