Chemical bonding in ordered Ce overlayers on Si(111)

Ordered Ce overlayers on Si(111) surfaces having √3 × √3 and 2×2 structures with metal coverages of about (1/3 and (1/4 monolayers, respectively, have been prepared and studied by synchrotron-radiation photoemission. The valence-band and core-level spectra show that the Ce-Si chemical interaction increases along the series 2×2, √3 × √3 , and bulk ${\mathrm{CeSi}}_2$, which is associated with increasing Si coordination for the Ce atom. The results are shown to be consistent with cluster-induced reaction and subsequent heterogeneous interface formation at the Ce/Si (111) interface. They suggest the importance of the interplay between Ce—Si, Si—Si, and Ce—Ce bonding in determining interface structures and chemistry.