The effect of flow on radiolysis in liquid phase-TEM flow cells

Abstract

Applying a continuous flow to rinse radiolytic species from the irradiated volume is a widely proposed strategy to reduce beam-related artefacts in Liquid-Phase Transmission Electron Microscopy (LP-TEM). However, this has not been verified either experimentally or theoretically to date. Here we explore an extended numerical model implementing radiolytic chemistry, diffusion and liquid convection to study the peculiarities of beam-induced chemistry in the presence of a flowing liquid within a heterogenously irradiated nanoconfined channel corresponding to a LP-TEM flow cell. Intruigingly, the concentration of some principal chemical species, predominantly hydrogen radicals and hydrated electrons, is found to grow significantly rather than to decrease in respect to zero-flow when moderate flow conditions are applied. This counterintuitive behaviour is discussed in terms of reactants’ lifetimes, spatial separation of the reaction network and self-scavenging by secondary radiolytic species. In the presence of a flow the consumption of highly reactive species is suppressed due to removal of the self-scavengers, and as a result their concentration in the irradiated area increases. A proof of concept for the supply of scavengers by the flow is demonstrated. Unravelling the effect of flow on radiolysis spawns direct implications for LP-TEM flow experiments providing yet one more control parameter for adjusting the chemistry in the irradiated/imaging area, in particular for mitigation strategies by continuous supply of scavengers.

Keywords

• liquid phase electron microscopy
• finite element simulation
• radiolysis
• reaction kinetics
• fluid flow and diffusion
• nano-confinement