Oil contamination in SEMs is a common problem. It manifests itself as dark spots and carton buildup in low KV scans and oil condensation on EDX detector windows. While one of the most common sources of this contamination is oil backstreamed from the roughing pump, other sources include pump oils, lubricants, seals, fingerprints, and the samples themselves. Depending upon severity, this effect ranges from a minor irritation to a very major problem.

Historical solutions to this problem have included turbomolecular pumps (TMP), cryopumps, drag pumps, traps, better pump oils, cooler running roughing pumps, double diffusion pumps and fractionating diffusion pumps. Many of these solutions have proved to be costly, require much maintenance and/or have not been very effective.