eDrop · Droplet Photoelectron Imaging

Angle-resolved photoelectron spectroscopy of aerosol droplets (“droplet photoelectron imaging”) is a novel approach to study fundamental aspects of the electron dynamics in liquids and across interfaces. Our recent proof-of-principle studies demonstrate that droplet photoelectron imaging not only complements, but also significantly extends the range of accessible information over established methods. Two aspects are unique to droplets: Firstly, the droplet size can be varied over a wide range from submicrons to microns. While large droplets provide overlap with liquid microjet and bulk studies, small droplets offer additional control by acting as efficient optical resonators. These optical cavity effects can be exploited to control where in the droplet the photoelectrons are generated; e.g. surface versus volume. Secondly, comprehensive information about photoelectron kinetic energy and angular distributions can be obtained fast and in a straightforward way by velocity map imaging.Building on our proof-of-principle studies, we propose to exploit the versatility of the droplet approach to address fundamental questions regarding electron dynamics in liquids and across interfaces: Can this new tool provide the missing data for low-energy electron scattering in water and other liquids and resolve the issue of the “universal curve”? How do slow electrons scatter across liquid-gas and buried liquid-liquid/solid interfaces and how does this depend on the composition and curvature of the interface? How is the ultrafast relaxation dynamics of electrons following above-band-gap excitation influenced by electron scattering and confinement effects? Low-energy electron scattering is a determining factor in radiation chemistry and biology and a central aspect of the solvated electron dynamics, while interfacial processes play a key role in atmospheric aerosols. Droplet photoelectron imaging opens up new ways to study such phenomena.