Spectroscopy of Solids, Gases, and Liquids in the ETEM

The use of various nanospectroscopies for determining the nanoscale composition and electronic structure of materials in the environmental transmission electron microscope (ETEM) is described and illustrated. ETEM is a powerful approach for determining the atomic level changes taking place in materials as a result of interactions with ambient gas or liquid environments. A variety of different composition changes may occur with the details depending on the sample composition, gas composition, temperature, and other stimuli. Changes in the elemental and bonding information associated with gas-solid interactions can be detected and quantified using electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX). When these spectroscopies are used in combination with the sub-nanometer electron probes associated with scanning transmission electron microscopy (STEM), they provide a powerful tool for determining composition and bonding information at the atomic level. It may also be important to monitor the surrounding gas or liquid composition during in situ experiments. The use of EELS and mass spectrometry, usually a residual gas analyzer (RGA), for gas measurement during ETEM experiments is described and compared. Examples of the application of nanospectroscopies to in situ analysis of compositional changes in a number of metal and oxide systems are given. Combining gas analysis with structural determination opens the door to an operando approach to TEM. Several examples of operando TEM applied to catalytic CO oxidation reactions are given. The impact of current and future instrument development on the analytical capability of ETEM is briefly described.