Agust Olafsson

Chemistry and Biochemistry

Faculty Advisor: Jon Camden

Infrared Nano-spectroscopy of Plasmonic Materials Using High-resolution STEM-EELS

Understanding how to harness energy at the nanoscale is critically important for the rational design of the next generation of materials engineered to transduce charge, heat, or energy to their local environment. These properties are encoded in the local and bulk dielectric response as well as in particle morphology and cluster geometry, which give rise to the collective resonant excitations sustained by plasmonic and phononic materials [1]. Despite recent progress made using optical spectroscopies, a detailed picture of energy flow at the nanoscale is obscured by the diffraction limit, making spatially-resolved measurements increasingly difficult for low energy phenomena such as infrared (IR) plasmons and lattice vibrations. This research seeks to overcome this limitation by utilizing electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM) to characterize the IR responses of plasmonic nanoparticles. We achieve this by using the current generation of aberration corrected and monochromated instruments which have significantly improved the ability to probe the IR regime with high energy resolution (<6 meV). STEM-EELS combines sub-nanometer resolving power with the capability to interact with a full spectral range of target excitations, making it the ideal technique to observe resonance behaviors for single particle and few particle systems [2-3]. These capabilities will be leveraged to detail the fundamental mechanisms of energy gathering and dissipation in plasmonic systems that underlie a broad variety of energy focused applications such as IR-photocatalysis, photovoltaics, surface-enhanced spectroscopy, and more [4-5].

[1]    Maier, Stefan Alexander. Plasmonics: fundamentals and applications. Springer Science & Business Media. 2007.
[2]    Masiello et al. Characterizing Localized Surface Plasmons using Electron Energy-Loss Spectroscopy. Annu. Rev. Phys. Chem. 2016, 67, 331-357.
[3]    Camden et al. Probing nanoparticle plasmons with electron energy loss spectroscopy. Chem. Rev. 2017, 118(6), 1994-3031.
[4]    Hutter et al. Exploitation of localized surface plasmon resonance. Advanced Materials, 2004, 16(19), 1685-1706.
[5]    Willets et al. Localized surface plasmon resonance spectroscopy and sensing. Annu. Rev. Phys. Chem. 2007, 58, 267-297.