Quantitative Scattering Microscopy (QSCAT) for Nanoscale Imaging of Ion Insertion Chemistry

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With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, a research team led by Justin Sambur and Randy Bartels of the Departments of Chemistry and Electrical and Computer Engineering, respectively, at Colorado State University is developing quantitative scattering microscopy, or QSCAT, a new microscopy approach that uses light to quantify the number of ions in a host material. Accurate and precise measurements of ion concentrations are critical to the successful operation and performance of many technological applications that benefit society, including lithium-ion batteries, energy-saving electrochromic “smart” windows, water desalination systems, ion separation membranes, and neuromorphic transistors. The problem with current electrical-based measurement approaches is that one electron detected in the electrical circuit does not always equal one ion inserted in the host material. To address this measurement selectivity problem, the research team will leverage the fact that inserted ions change the way light travels through a material to develop a light scattering-based measurement technique (QSCAT) that exploits the acute relationship between optical and electronic properties of solids. This research project seeks a simple, selective, sensitive, quantitative, and high-throughput optical microscopy technique to quantify ion insertion chemistry at the single nanoparticle-level. The development of QSCAT microscopy has the potential to accelerate materials characterization and, therefore, the discovery and development of functional materials that impact and benefit society. The project provides training opportunities that will help build a diverse scientific workforce, including training opportunities for students from groups that are underrepresented in science.The QSCAT microscopy technique being developed by the research team uses quantitative phase and field amplitude information related to the light that scatters from single particles (or localized regions on a surface) in order to selectively measure ion insertion processes in a host material. This approach isolates the ion-insertion process from all other processes that contribute to the electrochemical current response (for example, double-layer charging, solid electrolyte interphase (SEI) layer formation, corrosion, interfacial charge transfer), and does so via widefield imaging where hundreds of particles can be studied in a single experiment. The intellectual merit of the project will be the development of a robust and simple quantitative phase method that extracts the real and imaginary parts of the optical susceptibly perturbations of an ion insertion host. Because the approach is not a form of interferometric microscopy with coherent laser light, the current state-of-the-art in the field, QSCAT should reduce or eliminate issues such as multiple reflections, surface quality, dust contamination, thermal drift, fluid flow, and sample stability that ultimately limit sensitivity and selectivity. The research has the potential to enable new electroanalytical methods to interrogate charge storage mechanisms and surface chemical processes at the single nanoparticle level by allowing researchers to quickly determine structure-property relationships for systems of interest that cannot be interrogated with current optical microscopy approaches. Understanding higher-level effects, such as how particle morphology and exposed surface facets contribute to reactivity, has the potential to provide critical design principles that could be used to advance materials discovery. The broader impacts of the work include the potential to provide new insights into the behavior of materials that are important for energy storage and other important applications, as well as dissemination of the work through educational and outreach activities related to the research.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.