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Preparing samples for the transmission microscope
Electron Microscopy Service Preparing samples for the transmission microscope  ...

As the TEM image depends on whether the electrons can pass through the sample, it must be sufficiently thin to allow this. The goal of all the preparation techniques, for material and biological samples, is to achieve a very thin section of the sample, less than 100 nm, affecting its original structure as little as possible.

Preparing biological TEM samples

Preparing these samples generally follows the same basic protocol: chemical fixation, washing, dehydration in increasing concentrations of alcohol or acetone, embedding in resin and polymerisation. Depending on the aim, some of these steps include a staining stage with heavy metals such as osmium, tungsten or uranium. In any case, the user must do this in their laboratory.

The next step consists in obtaining very thin sections of the polymerised material using an ultramicrotome available at the Service.

Preparing powdered material TEM samples

Preparing these samples consists in diluting a very small quantity of the sample in an organic solvent that does not affect it, usually dichloroethane or acetone. Water can also be used if there is no alternative. The next step is to seek maximum dispersion by immersing the solution in an ultrasonic bath; after a time, a drop can be placed on the carbon-filmed grid for observation once dry.

The Service provides the user with all the elements needed for this process.

Preparing compact material TEM samples

This type of sample requires a thinning process that uses various apparatus. Firstly, the user must provide a sample no more than 200 µm. thick. Next, the first step is to cut a disk of 3 mm in diameter using the Ultrasonic Disk Cutter as this is the size of the sample that can be used in the TEM. The next step is to grind the disk on both sides with the Dimpling Grinder to obtain a central area of around 20 µm. This disk is placed in the Ion Mill so that it is attacked on both sides with argon ion beams until they make a small central orifice surrounded by a sufficiently thin area.

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