Quantifying Aqueous Radiolytic Products in Liquid Phase Electron Microscopy

Abstract

Liquid phase electron microscopy (LPEM) is rapidly gaining importance for in situ studies of chemical processes. However, radiolysis due to interactions between the liquid medium and the electron beam results in the formation of highly reactive species that influence the studied processes. Our understanding of LPEM radiolysis is currently based on simulations that rely on data collected from measurements at low electron flux intensities, requiring extrapolation by several orders of magnitude to match the intensities utilized in LPEM. We demonstrate direct electrochemical measurements of radiolytic products during in situ LPEM, which allows us to directly assess the high flux accuracy of low-flux radiolysis models. Using a specially designed liquid cell for electrochemical detection, we quantify the primary expected stable radiolysis products H 2 and H 2 O 2 in a scanning electron microscope. We find H 2 production is rapid and in reasonable agreement with predictions, but H 2 O 2 levels are lower than expected from the low-flux extrapolated radiolysis models. This study demonstrates a new approach to experimentally validate simulations and indicates that the chemical environment may be far more reducing than predicted from current models.

Precision of Radiation Chemistry Networks: Playing Jenga with Kinetic Models for Liquid-Phase Electron Microscopy

“…As main products, we consider relatively stable chemicals (e.g., H 2 O 2 decomposes slowly) that are experimentally accessible in situ , e.g., via electron energy loss spectroscopy or electrochemical approaches . For pure water, this denotes H 2 , H 2 O 2 , and O 2 .…”

“…As main products, we consider relatively stable chemicals (e.g., H 2 O 2 decomposes slowly) that are experimentally accessible in situ, e.g., via electron energy loss spectroscopy 33 or electrochemical approaches. 34 For pure water, this denotes and O 2 . Moreover, we track the parameters defining the acidity under irradiation, namely the radiolytic acidity π* and the radiolytic ion product K W *.…”

“…It is worth noting that albeit the G-values used within this work provided simulations with excellent agreement with experiments in LP-TEM, 20 they appear not to fully explain phenomena during cryo-TEM 44 or liquid-phase SEM. 34 Yet, for sparsening the kinetic model, this is of minor importance, as shown in Supporting Figures S23 and S24. Consequently, the model with reduced complexity is believed to be applicable for adjacent high dose rate low LET irradiation, 47 such as γor (hard) X-rays.…”

“…It is worth noting that albeit the G-values used within this work provided simulations with excellent agreement with experiments in LP-TEM, they appear not to fully explain phenomena during cryo-TEM or liquid-phase SEM . Yet, for sparsening the kinetic model, this is of minor importance, as shown in Supporting Figures S23 and S24.…”

Unraveling chemical processes during nanoparticle synthesis with liquid phase electron microscopy and correlative techniques

“…74,75 Recent results from Mølhave lab directly quantified radical production in aqueous solution using electrochemistry and found evidence of hydrogen and sulfate radical production, but not hydrogen peroxide production. 76 The absence of hydrogen peroxide is in direct contrast to expectations from radiolysis models; however, the hydrogen peroxide concentration could be below the detection limit of the electrochemical measurement. Taken together, these results provide initial experimental evidence suggesting that LPTEM researchers should use literature G -values and rate constants derived from low dose rate experiments with caution and consider performing experimental data fitting or direct measurements to evaluate radiolysis kinetic parameters.…”