AG SEGREGATION AND EPITAXIAL CR GROWTH ON AG(100)

The crystallographic and electronic structure of Cr films deposited on an Ag (100) crystal is studied by angle resolved photoemission. Both valence band and photoelectron forward scattering data show that body-centered-cubic Cr grows epitaxially on Ag (100) held at room temperature during deposition. Yet the Cr film is not uniform and exhibits a poor long range order. As soon as bilayer islands are formed and up to coverages as high as approximately 60 layer equivalent (LE), the growth of Cr films is invariably accompanied by surface segregation of Ag. Apparently monolayer islands formed initially are free of segregated Ag. This is confirmed by a study of the flat well-ordered Cr monolayer formed when one LE is deposited on the substrate heated at approximately 440 K [C. Krembel, M. C. Hanf, J. C. Peruchetti, D. Bolmont, and G. Gewinner, J. Magn. Magn. Mater. 93, 529 (199 1); C. Krembel, M. C. Hanf, J. C. Peruchetti, D. Bolmont, and G. Gewinner, Phys. Rev. B 44, 8407, 11472 (1991)]. In spite of the higher substrate temperature during deposition we could not find any evidence for the presence of segregated Ag on top of the ordered Cr monolayer. Possible reasons for this peculiar behavior, namely that Ag segregation takes lace on bi- or multilayers of Cr but not on the monolayer, are discussed.