The use of radiation chemical methods in liquid cell electron microscopy: main concepts and limitations
By: Patricia Abellan - SuperSTEM Laboratory, SciTech Daresbury campus, United Kingdom
Radiolytic synthesis routes and wastewater remediation methodologies exploit the chemical effects produced by the interaction of high-energy γ-rays and electrons with liquids to produce nanomaterials and to break-down water pollutants, respectively. In the (scanning) transmission electron microscope, (S)TEM, the formation and degradation dynamics of nanomaterials can be investigated in-situ using the effect of the 60-300kV incident electrons in combination with liquid cells. Many theoretical and experimental efforts have been devoted to understanding how irradiation in the (S)TEM affects DI water and different aqueous solutions, since water is the most common solvent used in the electron microscope. Furthermore, radiation chemists have used water for decades for general kinetics studies, thus producing a large amount of information that is now available for potential EM applications. These kinetics studies provide a base to understand drastic experimental differences observed when small changes to the initial composition of the solution are made. For instance, competing kinetics can explain why the pH decreases during irradiation of DI water while it can increase when including certain solutes in the solution. More generally, radiation-chemical methods can be applied to liquid cell experiments to tune the environment for specific applications in the fields of chemistry and materials sciences.
In this seminar I will introduce experimental conditions for which the solvent in a solution dictates the radiation chemistry during in-situ liquid cell EM, which main factors change the production of radicals and the basics of competing kinetics in radiation chemistry. I will discuss the case of water more in detail but also introduce some general concepts on the radiation chemistry of organic solvents and specific properties that can benefit liquid cells experiments; such as the possibility of minimal production of reactive species or of net production of molecular species of lower reducing/oxidizing power. Finally, I will discuss general methods for finding more suitable synthesis/corrosive environments for controlled nanoparticles formation or dissolution using the electron beam by either reproducing a selective reducing or oxidizing environment and show examples in the (S)TEM when available.