## For use in SEM ### What matters SEM chambers are made from high magnetic permeability materials as to shield the beam from interfering magnetic fields. This also applies to port covers or adapters. Vacuum performance is another consideration, but the requirements for most chambers are not as strict as say the electron gun area. ### Common metals and their suitability - Stainless Steel - Most common stainless alloys are not magnetic, and thus have poor shielding properties. This includes 304 and 316 stainless. - 400 series are somewhat magnetically permeable. If they are good enough or not largely depends on the magnetic environment the microscope is in. If theres a 60hz field concern, or interference is already visible they are probably not the best option. - Iron - Straight iron is one of the best options WRT to magnetic shielding, but can be more difficult to work with from a fabrication standpoint - Many SEM chambers and components are made from cast iron. Vacuum outgassing performance suffers some, but the trade off for much lower susceptibility to interference is usually considered more important. - Electrical Steels (silicon steels) - Electrical steel can be a good compromise. Usually more chemically resistant and easier to machine, but magnetic permeability can depend on many factors. Resources: https://www.softmagneticalloy.com/selecting_soft_magnetic_alloys.html https://en.wikipedia.org/wiki/Electrical_steel https://en.wikipedia.org/wiki/Permeability_(electromagnetism)