EPSCoR Research Fellows: NSF: Monochromated STEM EELS of intercalated 2D materials bilayers

This Research Infrastructure Improvement (RII) EPSCoR Research Fellows project provides a fellowship to an Assistant Professor and training for a graduate student at Brown University. This work is conducted in collaboration with Dr. Jordan Hachtel at Oak Ridge National Laboratory (ORNL). Through the fellowship, the PI will study how sodium and potassium atoms behave when inserted between layers of ultrathin materials such as graphene and molybdenum disulfide (MoS2), including how much electrical charge passes from these atoms into the surrounding material. This matters for two reasons: it could inform energy storage technologies that rely on abundant sodium and potassium rather than scarce, strategic lithium, and the transferred charge can also change the electronic behavior of these materials in ways that may be harnessed in future quantum technologies. The project draws on physics, chemistry, and materials science, using one of the world's few electron microscopes equipped to resolve minute, atomic-scale energy changes in these materials. The fellowship will train a new researcher, build a lasting partnership between Brown University and the national laboratory, and support U.S. leadership in energy storage and quantum technologies. This project uses monochromated scanning transmission electron microscopy (STEM) electron energy loss spectroscopy (EELS), achieving sub-10 meV energy resolution, to characterize sodium (Na) and potassium (K) intercalation in two-dimensional (2D) materials bilayers: homo-bilayers of graphene or MoS₂, and graphene/MoS₂ hetero-bilayers. While atomic-resolution imaging will resolve intercalant ordering, the project's central contribution is spectroscopic: quantifying charge transfer between the intercalated atoms and their 2D hosts, resolving vibrational and electronic fine structure inaccessible to conventional, non-monochromated instruments, and correlating intercalant distribution with structural phase transitions in the MoS₂ host. Sample preparation will be performed at Brown University, with spectroscopic characterization conducted at ORNL's Nion HERMES instrument, one of few systems worldwide offering both atomic-resolution imaging and single-digit meV spectral resolution. This project will establish STEM EELS expertise at Brown, a capability currently unavailable within the Rhode Island EPSCoR jurisdiction, training a graduate student in advanced electron spectroscopy, and laying groundwork for future proposals in 2D materials, electrochemistry, and quantum materials science. This project is supported by the EPSCoR Research Infrastructure Improvement Program: EPSCoR Research Fellows, which supports early- and mid-career investigators in eligible jurisdictions to develop collaborations at the nation’s private, government or academic research institutions. 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.