Photoelectron spectroscopy studies of growth, thermal stability, and alloying for transition metal-tungsten (111) bimetallic systems

High-resolution soft-x-ray photoelectron spectroscopy using synchrotron radiation is used to study late-transition-metal films (Pt, Pd, Ir, Rh) on W(111). It is found that the films grow in a layer mode at 300 K. A single physical monolayer (ML) of each of these metals "floats" on the tungsten substrate and, upon annealing to T>700 K, the metal film-coated W(111) becomes faceted, i.e., covered with three-sided pyramids exposing {211} planes. During growth of Pt, Ir, and Rh films, at 300 K, for coverages exceeding 1 ML, atomic mixing at the interface is observed, driven by energy released in the adsorption process. Multilayer films of these metals on W(111), upon annealing, undergo complex transformations which include alloying, segregation, cluster formation, and faceting of the surface between clusters. It is demonstrated that despite the unusual complexity of the problem, soft-x-ray photoelectron spectroscopy allows for successful investigation of these transformations.