The structure of low-coverage Ti and V on the Al(001) crystal surface

Abstract

The BFS (Bozzolo-Ferrante-Smith) Method for Alloys predicts that V and Ti would be effective interlayers to act as a diffusion barrier between a metal substrate and metal overlayer. Previous work from our group using the RBS channeling technique, determined that Ti is an effective interlayer between Fe and the Al(001) bulk substrate. The Fe-V-Al(001) system was not treated in this earlier work. This thesis is focused on studying the structure of the first bi-metal interface of these tri-metal systems, i.e. the Ti-Al(001) and V-Al(001) interfaces. LEIS (low-energy ion scattering spectroscopy) and LEED (low-energy electron diffraction) were used as experimental techniques specifically designed to study the surface structure of the top few layers of sample surfaces. LEED images for the Ti-Al case gave a c(2 x 2) pattern, a change from the standard p(1x1) pattern of the clean Al(001) surface, suggesting Ti occupies every other Al lattice site. LEIS results suggest that Ti prefers subsurface occupancy for sub-monolayer Ti coverage, and fills the surface layer as deposition thickness increases above but near 1 ML. LEED images for the V-Al system produced nothing out of the ordinary, but rather display a blurry p(1x1) image, becoming less distinct as V deposition thickness increases, suggesting that V atoms place themselves in the Al substrate with no specific order. LEIS results suggest that V prefers sub-surface occupancy for both sub-monolayer and higher (up to 2.5 ML) V coverage. Contrasting the results of these experiments, we determined that the structural characteristics of the V-Al interface differed enough from those of the Ti-Al interface, to conclude that V cannot be considered as effective of an interlayer as Ti.