Matter-Beam Interactions: Photochemistry with Virtual Photons?

It has recently been appreciated that the convergent electron beams used in scanning transmission electron microscopes (STEMs) can not only be employed for purposes of structural determination, but also for inducing local chemical transformations. STEMs have already been used to build heterostructures from substitutional defects in two-dimensional materials with atomic precision; a feat with transformative technological implications. However, the mechanisms underlying the chemical processes initiated by the matter-beam interaction are not yet well-understood. I will present our recent progress towards first principles methods for describing the electronic response of materials to high energy electron irradiation. I will also discuss the selection rules for electronic excitations that can occur in the materials, which depend explicitly on the incident electron's point of impact. Finally, I will give an overview of a study in which these methods are applied to reveal defect-centered excited states of silicon-doped graphene nanostructures, and the effects of beam-induced population of these exited states on the reactivity of the silicon defect.