Instead, we believe they derive from silicide structures. The next sections detail the formation of such surfaces and describe their possible structure. The experiment was done with a similar sample and techniques as those used in the previous Au and Mg experiments. The prime difference in the Ce experiment was the evaporation of Ce metal.
Cerium is a very reactive metal and quickly tarnishes in air.
For this reason, Ce would have to be evaporated from the liquid state at approximately 1100 C with a vapor pressure of 2E-7 Torr. However, since liquid Ce is denser than the very stable oxide, ceria, it was necessary to use oxide-free source material, otherwise the ceria could float above the liquid cerium and hinder any evaporated Ce from reaching the Si sample surface. High purity Ce was obtained from Ames Laboratory, Iowa State University, sealed in glass ampules. The boat was mounted in the vacuum system 10-cm away from the sample surface and inclined at a 30 degree angle. Initially, the Ta boat required 60 Amperes to reach roughly 800 C and melt the Ce.