Impurity-induced 900 °C (2×2) surface reconstruction of SrTiO₃(100)

A p(2×2)surface reconstruction is observed over the 800-900 °C range for SrTiO₃ (100), the temperature range which is used in the oxygen anneal of Y, Ba, Cu layers on SrTiO₃ (100) substrates in the synthesis of high T_c superconducting thin films. As observed by Auger electron spectroscopy, high-temperature annealing causes calcium to segregate to the surface. Initially, at a Ca content of 3% upon a SrO-terminated SrTiO₃ (100) surface, the Ca atom is incorporated in a superstructure, which is attributed to multiple scattering across the two topmost interfaces. When the surface Ca content is below 1% the p(2×2) surface reconstruction is induced. The p(2×2) surface reconstruction disappears when the calcium content is removed.