Sample insertion and beam activation
- To use the SEM you must first place a sample in the sample chamber. Some machines have a setting that says ‘exchange position’. If so, check that the receiving stage inside the chamber is set at the exchange position.
- Since the sample chamber is kept under vacuum, you must introduce air into the chamber in order to open it and place the sample inside on the stage. This is called venting the chamber. Some machines have a small specimen exchange chamber attached to the main chamber and this is the region vented.
- Once the sample is placed in the sample chamber, you must remove the air by pumping it out again. This is called evacuation. It is worth bearing in mind that your sample should be able to survive exposure to a vacuum. Some specialised sample preparation may be needed (see main menu: Sample preparation). However, there are a range of SEMs and some of them work at lower vacuums, allowing wet samples to be viewed. Others allow viewing of frozen samples.
- While you are waiting for the machine to reach its correct vacuum you can select the electron beam voltage that you will need to use (but don’t turn it on yet). Delicate samples such as many polymers and biological materials are better viewed under a beam of lesser intensity than most geological materials or metals.
- Once the chamber has reached a suitable vacuum (this will be different on different machines), you can turn on the electron beam.