It was suggsted by a few that since the film is outgassing it is OK to backfill a TEM with lab air which has a high moisture content because the film in the camera chamber has a significant outgassing rate. My general comment is that you want to keep as much water and oxygen out of a vacuum system as possible. There is no need to add more to what may already be there.

In a vacuum system without any leaks or severe outgassing problems and with properly cleaned surfaces, the major factor which limits the ultimate pressure and pumpdown time is the water adsorbed on the exposed surfaces of the system. Depending on the type of surface, water molecules car either adsorb or chemisorb onto the surface. A chemisorbed species is characterized by having an exchange of electrons with the atoms on the surface and will have a higher energy associated with the desorption of the molecule from the surface.