Pumps and Holders

In the past three chapters we’ve described the sources, lenses, and detectors that make up a TEM. The only other parts of the instrument you need to know about in detail are those that, if you are not careful, can seriously degrade the quality of the information you generate even if the rest is perfect. These two parts are the holder in which you put your specimen and the vacuum that surrounds it. While there isn’t much you can do to improve the vacuum, beyond buying a better microscope, there is a lot you can do that will degrade the quality of the vacuum in the column and, in doing so, contaminate your specimen. So we’ll tell you a few basics about how the vacuum pumps work, and how the vacuum system is put together. Although the vacuum system is under computer control in most TEMs, you still affect the vacuum by what you put in the microscope. Consequently, you need to know what not to do on those occasions when you might otherwise degrade the vacuum.