Surface physics group of Prof. Jürg Osterwalder at the University of Zürich

The evaporation of rare earth metals like cerium and its use as getter pumps for
the application in ultra high vacuum was invented in 1989. These pumps consist
in a droplet of rare earth material that is heated restively and evaporates onto the
walls of the recipient. Rest gas, particularly hydrogen will then stick on this reactive
surface and diffuse in the film. This type of pump has been successfully applied in
different UHV experiments where base pressures below 10-10 mbar were attained
routinely.

The following points compare the rare earth getter pumps with commercial Ti getter
pumps:
1) The pumping speed per unit area is about twice as large as that of Ti getter pumps.
2) The pumping volume is much larger than that of Ti getter pumps since the pumped
gases may diffuse easier in the bulk of rare earth metals. From this follows a much
larger pump lifetime per evaporation cycle.
3) The pumping surfaces do not have to be cooled with liquid nitrogen.

The rare earth droplets may be purchased in a ready to use form from MatecK, Jülich.