The Radiation Chemistry of Vitrified Water Ice Interfaces Studied by Electron Energy Loss Spectroscopy

While the radiolysis of liquid water by high-energy electrons has been extensively studied by conventional radiation chemistry methods, the radiolysis of water at interfaces and inside an electron microscope and the radiolysis of water ice are still poorly understood. Electron energy loss spectroscopy (EELS) can be performed inside the scanning transmission electron microscope (STEM), and thus, can allow for in situ analysis of radiation damage effects. In frozen hydrated aqueous specimens, cryo-EELS has already been used to study radiation damage.[1-3] Using new monochromated sources, with higher energy resolutions on the order of &lt; 100 meV[4] and increased peak(signal)-to-background (S/B) ratio, new insights on the radiation damage of materials have been recently made possible. Recently, we have shown that by using monochromated EELS at the oxygen K-edge and at cryogenic temperatures on thin films of ice, all radiolysis products (radicals and molecules) of water ice can be resolved (except for H₂ and .H)[5]. We also discussed the effect of different microscope parameters on the radiolysis of water ice and proposed a new high dose reaction scheme. In order to apply this method to the study of any water ice interface, samples must be prepared without artefacts caused by water loss or by the freezing process. Methods to monitor the vitrification process are thus relevant. For instance, low frequency Raman spectrometry can reveal the crystalline structure of ice and can also be used in combination with FIB/SEM to probe the depth of vitreous ice in plunge-freezed vitrified samples.[6] Additionally, certain materials with very high water content, such as hydrogels, are extremely sensitive to the cryofixation process process and will directly show if unsuccessful. Here we discuss our latest results on the study of the radiolysis of water ice interfaces and on the challenge of discerning whether vitrification at water interfaces has been truly achieved.[7]<br/><br/><i>References:</i><br/>[1] M.A. Aronova et al., Micron <b>42</b> (2011), 252–256, doi: 10.1016/j.micron.2010.10.009<br/>[2] R.D. Leapman and S. Sun, Ultramicroscopy <b>59</b> (1995), 71–79, doi: 10.1016/0304-3991(95)00019-W<br/>[3] R.F. Egerton, Ultramicroscopy <b>5</b> (1980), 521–523, doi: 10.1016/S0304-3991(80)80009-X<br/>[4] T.C. Lovejoy et al., Microsc. Microanal. <b>24</b> (2018), 446–447, doi: 10.1017/S1431927618002726<br/>[5] P. Abellan, E. Gautron, and J.A. LaVerne, J. Phys. Chem. C <b>127</b> (2023) 15336–15345, doi: 10.1021/acs.jpcc.3c02936<br/>[6] M. Essani et al., Anal. Chem. 94 (2022) 8120-8125, doi: 10.1021/acs.analchem.2c00245<br/>[7] MJ and JLB were supported by the ANR PRC OverBONE project (ANR-20-CE18-0015). HN and PM were supported by the OPINCHARGE project, which received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No 101104032 — OPINCHARGE. PA’s and EG’s work on cryo-EELS is supported by the ERC-2023-CoG project DREAM-SWIM (Project # 101124066). JAL was supported by the Division of Chemical Sciences Geosciences and Biosciences, Department of Energy, Office of Science, Basic Energy Sciences, grant number DE-FC02-04ER15533. Measurements were performed using the IMN’s characterization platform, PLASSMAT, Nantes, France.