The specimens examined by SEM must be able to withstand the strong electric currents produced by the electron beam. Samples that do not conduct electricity can be damaged by the charges that can build up. Non-conductive specimens must first be coated with a thin layer of conductive material. This coating is accomplished using a sputterer. A sputter coater produces a nanometer thickness of conductive material on the surface through a cold plasma process that retains the contours of the specimen.

Since most biological samples are non-conductive, they must be sputter coated. However, many of these samples also need additional treatment prior to sputter coating to prevent the cells from collapsing under the intense electron beam. The types of treatments vary according to the specimens. This usually involves a process that fixes the components of the specimen. For example, gluteraldehyde can be used to crosslink the proteins to form rigid polymers. The tissues then need to be rinsed in a buff er followed by dehydrated. Dehydration can be as simple as adding ethanol or more complicated using freeze drying or critical point evaporation.

Once the specimen is fixed, it is then glued to a sample holder or "post." The post is placed into the sputter coater until a thin layer of gold is applied to the surface. The specimen is then placed in the SEM vacuum chamber and the electron gun is switched on.

Proceed to SEM start-up procedure.

Last update: May 8, 1998.