Double-Pass Electron Energy Loss Spectroscopy of Suspended Split-Ring Resonators

Abstract

Swift electrons passing near metal-dielectric interfaces can excite travelling electromagnetic waves confined to the charge density at the interface, known as surface plasmon polaritons (SPPs). The excitation process retards the swift electrons to an extent which can be resolved using electron energy loss spectroscopy (EELS). Scanning transmission electron microscopy (STEM) paired with EELS can characterize these losses with high energy and spatial resolution but is a time-averaged technique. Hence, spectral data provides statistical information about the number of electrons which underwent a particular energy exchange, but their existences are otherwise spatiotemporally ambiguous. We have developed and tested a scheme which partially lifts this veil. This thesis details the steps taken to fabricate a split-ring resonator so that single electrons sequentially pass by both ends of the resonator, enabling what we refer to here as double-pass EELS. We provide evidence that single electrons have excited SPPs in both events, and that this aloof analogue to common plural scattering may also lead to an amplification in the second event. This suggests that our technique could be considered a single electron pump-probe spectroscopy, with wide-ranging applications, particularly in quantum research.