What you need to know about TEM grids!

General Information:
EM grids are generally used in TEM. A TEM grid is typically a flat disc with a mesh or other shaped holes used to support thin sections of specimen.
The holes in the grids allow the electrons to pass through. Grids are available in a wide variety of patterns and materials for various applications.


Standard Diameter:
The standard diameter of grids is 3.05mm but there are also special instruments that use different diameter versions (e.g. 2.3mm).


The most common grid types:
The most commonly used grids are 200 mesh, 300 mesh and 400 mesh square grids in copper.


Mesh – what is that?
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 85µm. Obviously on any grid you need to have bars and open areas. Therefore the 85µm are made up of a 60 micron hole and 25 micron bar (dimensions vary with different mesh numbers).


Which grid materials are available?
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 aluminum. Some copper grids are flash coated on one side with either rhodium or palladium to enable users to differentiate more easily between the faces and to stop tarnishing. Most grids have one shiny side and one matt side.


Why support films/coating?
Many specimens 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.


What are Finder grids?
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.


Packaging of grids:
Grids are normally supplied in anti-static vials to make them easier to remove and use.