Modulating single molecular electron sources with light: Opportunities and challenges

Applying a strong, constant electric field at single-C-60 molecule protrusions formed on a metallic substrate can cause electrons to be emitted from individual single molecules into a vacuum. The shapes of such single molecular electron sources reflect the shapes of the molecular orbitals from which the electrons originate. By illuminating the source with light pulses, photo-excited electrons can be emitted from different molecular orbitals, thereby modulating the electron sources at a subnanometric scale. In this context, we discuss the opportunities presented by this light-induced modulation of electron emission for developing a unique scheme to integrate ultrafast switches into a single molecule and for advancing high-resolution, ultrafast electron microscopy. We also discuss the experimental and theoretical challenges associated with this approach, such as the requirements for picoscale stability and controllability of molecular positions, as well as the need for large-scale ab initio calculations under strong constant fields.