Contamination of holey/lacey carbon films in STEM

In many cases, the key to obtaining good TEM results is in the sample preparation itself. Even once a thin specimen is achieved, other factors determine how well the sample will behave in the microscope. One of the main hindrances to TEM and STEM–EELS analysis is the build up of carbon contamination on the sample under the electron beam. This process may occur due to the nature of the sample itself or the support grids or films on which the sample sits. Here, we investigate contamination on holey and lacey carbon films from three different suppliers. We find that all grids have a large amount of mobile hydrocarbon contamination on them, as well as other larger contaminant species on the surface. Even after a variety of cleaning routines, none of the films are clean enough for STEM–EELS experiments requiring long acquisition times.

► Investigation of carbon films for STEM sample preparation.
► Three manufacturers are investigated.
► All grids contaminate badly.
► Plasma cleaning and heating are investigated as methods of mobile carbon contaminant removal.
► Manufacturers need to review their carbon film preparation methods.