Accessing the Solid-Liquid Interface of Materials at the Nanoscale Using Cryogenic Electron Microscopy and Spectroscopy

Cryogenic transmission electron microscopy allows for the observation of samples in near native conditions and for higher electron beam tolerances than room temperature observations. Crucially, it provides the opportunity of obtaining quantified information from solid-liquid interfaces. In practice, accessing the solid-liquid interface at high-resolution represents specific challenges that are sample dependent and that must be addressed. Typically, sample preparation for cryo-(S)TEM is central and as a matter of fact, a significant bottleneck in many experiments. For the case of hard-soft interfaces in hydrated systems there are additional challenges which arise by the mismatch between the bio(chemical), mechanical and physical properties of both sides of the interface. Imaging conditions that are suitable for the different electron scattering produced by the different materials must be found and there can be limitations by the fact that a specific site within the sample (with a specific orientation) must be accessed. In this presentation, I will show our latest experimental results and discuss the specific challenges met on the application of 3D Cryo-FIB/SEM to the study of hard-soft tissue interfaces, to probe biomolecules fouled in polymeric filtration membranes and for the analysis of biomaterials interfaces. One specific challenge that is common to all experiments in hydrated samples is to understand the effect of the electron beam in our observations to disregard possible artefacts. Despite the more limited diffusion of secondary species at cryogenic temperatures, the high-energy electron beam used to probe the sample will unavoidably induces chemical processes due to radiolysis. Methods to directly probe the effects of radiation chemistry inside the EM have not been developed yet. In this talk, I will also present our investigations combining scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) on ice and discuss the effects of high-dose rate electron irradiation on water and on water-solid interfaces in the EM.