GUIDE – EM GRIDS
- EM grids are generally only used in transmission electron microscopy (TEM). An EM grid is typically a flat foil disc with a mesh or other shaped holes used to support a thin section of specimen. The holes in the grids allow the electrons to pass through. They are available in a wide variety of patterns and materials to suit various applications.
- The standard diameter of grids is 3.05mm but there is the odd instrument that uses 2.3mm diameter versions.
- The most commonly used grids are 200 mesh, 300 mesh and 400 mesh square grids in copper.
- Mesh is the number of squares per inch, so a grid that is specified as 300 mesh will have a theoretical square size of approximately 85 microns. Obviously on any grid you need to have bars and open areas so it is common for this 85 microns to be made up of a 60 micron hole and 25 micron bar.
- Grids are available in various different materials as some specimens will react with certain materials and some require analysis at higher temperatures. Normal materials are copper, nickel, gold, molybdenum, titanium, stainless steel and aluminium. Some copper grids are flash coated on one side with either rhodium or paladium to enable users to differentiate more easily between the faces and to stop tarnishing. Most grids have one shiny side and one matt side.
- Many specimens will require an additional support on top of the grid to prevent them from falling through the holes. In these case a carbon or formvar coating is formed across the surface to provide support without interfering significantly with the flow of the electron beam.
- Finder or Index grids are used to identify specific areas of interest in specimens. This allows the interesting area to be relocated later or logged for reference.
- Grids are normally supplied in anti-static vials to make them easier to remove and use.
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