Four steps which are often necessary to prepare a specimen for viewing in the SEM are fixation, drying, mounting, and metal coating. Fixation and drying stabilize soft, moist specimens which otherwise would be deformed when exposed to the high vacuum in the SEM. Fixation entails hardening the specimen with a chemical or chemicals such as glutaraldehyde or formaldehyde. The specimen may then be air dried. However, freeze drying or critical point drying often are necessary because these methods cause less specimen distortion. After fixation and drying, large specimens are glued to aluminum specimen mounts. The specimen must be oriented so that the surface to be viewed is not obscured by the mount. Small particles may be dusted onto double-coated tape attached to the mount. The final preparative step involves coating the specimen with a thin metal layer which makes the specimen surface electrically conductive. The coating is necessary to ground the specimen so that the SEM's probe electrons do not accumulate and electrically charge the specimen. The metal layer is too thin to be seen by the SEM and usually does not cause loss of detail.

Not all the steps mentioned above are necessary to view every specimen. Dry, hard specimens such as plant seeds or minerals may not need fixation or drying. Specimens such as metals may already be electrically conductive and not need coating. Under some conditions, moist biological samples such as leaves and insects can be viewed with no preparation except mounting. Rapid freezing of fresh tissues is an alternate method of preserving the structure and chemistry of the sample. Our cold stage enables us to rapidly cool the sample to minus 190 degrees Celsius. Once the sample is frozen, any ice formed on the surface during freezing is removed by warming the stage slightly, until the ice sublimes.