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Coated Grids

The diameter of grids is standard, as 3.05mm. The thickness is variable based on the grid

materials. The thickness range is from 10um to 25um. The mesh of the grid is defined by the

number of hole within 1 inch. For example, the 200 mesh grid has 20 holes along diameter

direction, 400 mesh grid has 40 holes in diameter.

Since the diameter of grid is a standard length, 3.05mm, each hole size is less than ~200um

in 100 mesh grid, ~97um in 200 mesh grid, ~63um in 300 mesh grid and ~42um in 400

mesh grid.

Most samples for transmission electron microscopy must be "supported" on some kind of a

thin electron transparent film, to hold the specimen in place while in the objective lens of the

TEM. Only samples that are "self- supporting" do not need some additional support film.

Should an electron microscope user use a support film at all if one is not absolutely needed?

Probably not, because even the very best quality of support films do result in more material

being placed in the beam's path, resulting ,even if ever so slightly, in reducing the contrast ofthe final image. But for many users, they don't have the luxury of having to make that

decision: More often than not, even what appear to be self-supporting samples, still do need

the assistance of a support film to cut down on sample drift.

Types of coated grid available

Thin carbon film coated grids:

This is pure thin carbon film coated grid. The carbon film is very clean and pure. Thicknessof the carbon film is less than 10nm. Since the film is very thin and fragile, it requires delicatehandling during specimen preparation. We only coated it on 400 mesh grids. Glow dischargewill make the carbon surface less hydrophobic.

Thick carbon film coated grids:

This is pure thick carbon film coated grid. The carbon film is very clean and pure. Thethickness of the carbon film is about 35nm. Since the pure carbon film is very fragile, wedon't coat them on grids less than 200 mesh. Glow discharge will make the carbon surfaceless hydrophobic.

Carbon/Formvar film grids:

A 20-30nm Formvar film coated grid with a ~15nm layer of carbon. This is the strongest andmost versatile support film. It is stable in the EM under all operating conditions including highmagnification with high beam intensity. The films can withstand vigorous specimenpreparation techniques. If the carbon surface is hydrophobic, specimen suspensions can beapplied to the Formvar surface or glow discharged.

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The selection of the "right" support film has never been an easy exercise, even the mostexperienced of TEM experts, and the only way to really determine which support film is thebest for a particular application it to just "try it!" Therefore, we would like to contribute in auseful way to the needed information base to help make the optimum selections, but the

giving of such "guidance" itself is an imprecise science.

We have therefore broken down the different kinds of support films and have tried to presentthe "trade offs" between one support film system vs. another. We can offer no guarantees,since the range of samples studied is so wide and the environmental range so broad (fromcryo temperatures to temperatures exceeding 1000C) to which the grids and their coatingsmight be subjected. But the best decisions are usually made by just trying severalpossibilities and if one works better than the other, the choice for future samples becomesobvious.

Following table will help you determine which support film to use for your particulartransmission electron microscopy project.