Electron Energy Loss Spectroscopy with Phase Structured Probes

Advances in monochromation and aberration-correction in electron microscopy have made electron energy loss spectroscopy (EELS) a widely used tool in materials science. EELS has been used to map surface plasmons and phonon excitations. Typically, samples are excited using a focused probe or large planewave illumination. We study how electron beams can be structured with various techniques such as diffracting holograms or programmable phaseplates. Structuring the electron wavefunction allows the beam to be tailored to the symmetries of the sample. This can be used to probe specific excitations that would be traditionally inaccessible due to overlap with other modes in either spatial extent or energy. There is even the possibility of transferring quantum numbers such as orbital angular momentum (OAM) to the sample. We discuss the techniques required for these experiments as well as the theoretical and experimental work that is ongoing in this exciting area of electron microscopy.