Cleanliness
Specimen cleanliness is of paramount importance in the FE-SEM. Contamination of the sample will lead to poor image quality. High levels of specimen contamination can lead to outgassing in the vacuum environment. This can contaminate the entire specimen chamber.
Requirements
In order to avoid contamination, specimens that are put into this scope must also follow strict requirements.
All specimens must be clean!
They must be free of dust and debris. A compressed air can is available in every lab for dusting off each specimen before it goes in the scope.
Specimens have to fit in the microscope!
They must be able to fit through the specimen exchange chamber. NEVER force a specimen into the microscope! At minimum, it will destroy the specimen.
Specimens may require coating with a conductive surface!
Specimens that are not made of conducting material must be made conductive by applying a coating of either carbon, gold or a platinum/palladium mixture. The proper coating choice depends on the type of analysis needed for the specimen. For the FE-SEM, Pt/Pd is the best choice for imaging. The grain size of Pt/Pd is small, and therefore harder to see, even at high magnifications. For X-ray analysis, a thin layer of carbon is the best choice because the peaks of gold or Pt/Pd would show up in the middle of the spectrum. Coating thickness is also important. Surface decorations of heavy coatings are visible when imaging at high resolution and high magnification. To prevent this, Pt/Pd is applied to 5 nm thick.
There are two machines for coating in the Specimen Preparation Lab. Coating can be accomplished by asking the lab personnel.
Specimens must not outgas—they must be free of any liquid!
The specimens cannot be wet or have any liquid contaminants on or in them. When the hot electron beam interacts with a wet specimen, the liquid evaporates and outgasses into the sample chamber. This contaminates the vacuum systems and produces an unstable beam. The end result is a poor image. To dry specimens that contain liquid, store them in a desiccator or use an oven.
Specimens must be mounted securely to a specimen holder!
In order to use the full functionality of the FE-SEM, the specimens must be mounted securely to the specimen holder. This prevents the specimen from falling off the stage if the tilt function is used, and ensures a good conduction pathway for the electron charge. Metallic samples must be well secured to the holder, or they will be pulled off the holder at small working distances by the objective lens' magnetic field.