Measuring Carrier and Structural Dynamics of Silicon with Ultrafast Electron Energy-Loss Spectroscopy

Electron energy-loss spectroscopy (EELS) probes a material’s electronic and chemical properties by measuring the energy loss of electrons due to inelastic interactions with the material. Ultrafast electron microscopy enables EELS to achieve high spatiotemporal resolution, allowing for the mapping of charge transport and recombination after photoexcitation. We will discuss our current progress toward this goal, starting with early findings on a silicon (Si) thin film membrane. We measure both the volume plasmon and the L_2,3 edge of photoexcited Si to investigate carrier and structural dynamics. The excited carrier density is derived from the redshift of the volume plasmon peak, and a model based on density functional theory and the Bethe-Salpeter equation is employed to predict the transient Si L_2,3 edge. Additionally, we will discuss relationships between the volume plasmon and broadening in the Si L_2,3 edge that cannot be explored by using photons. Overall, our approach represents a crucial first step in analyzing ultrafast dynamics of photoexcited states in nanostructures, interfaces, and grain boundaries of materials for energy applications, highlighting its advantages over other ultrafast spectroscopy techniques.