An Open-Cell Environmental Transmission Electron Microscopy Technique for In Situ Characterization of Samples in Aqueous Liquid Solutions

TL;DR

This paper introduces a novel open-cell liquid TEM technique using salt particles and temperature control to form aqueous droplets in situ, enabling easier specimen preparation and potential in situ light source integration.

Contribution

The paper presents a new open-cell liquid TEM method that simplifies sample loading and allows in situ hydration using salt particles and temperature control.

Findings

Successful formation of aqueous droplets on salt particles in ETEM.

Enabling dry sample loading with standard TEM grids.

Potential for combining with in situ light sources for photocorrosion studies.

Abstract

The desire to image specimens in liquids has led to the development of open-cell and closed-cell techniques in transmission electron microscopy (TEM). The closed-cell approach is currently more common in TEM and has yielded new insights into a number of biological and materials processes in liquid environments. The open-cell approach, which requires an environmental TEM (ETEM), is technically challenging but may be advantageous in certain circumstances due to fewer restrictions on specimen and detector geometry. Here, we demonstrate a novel approach to open-cell liquid TEM, in which we use salt particles to facilitate the in situ formation of droplets of aqueous solution that envelope specimen particles coloaded with the salt. This is achieved by controlling sample temperature between 1 and 10{\deg}C and introducing water vapor to the ETEM chamber above the critical pressure for the formation of liquid water on the salt particles. Our use of in situ hydration enables specimens to be loaded into a microscope in a dry state using standard 3 mm TEM grids, allowing specimens to be prepared using trivial sample preparation techniques. Our future aim will be to combine this technique with an in situ light source to study photocorrosion in aqueous environments.