Growth and alloy formation of Pt on Fe(100)

The structure of the Pt/Fe(100) overlayer system is studied using high-energy ion scattering in combination with shadowing and blocking in the Pt coverage range 0–11 monolayers. Evaporation at a sample temperature of 300 K results in layer-by-layer growth of an elemental Pt layer. Annealing at a temperature above 575 K results in the formation of a ${\mathrm{Pt}}_{0.5}$ ${\mathrm{Fe}}_{0.5}$ layer. The alloy crystallizes into a body-centered tetragonal structure, matching epitaxially with the Fe(100) substrate, and with an atomic interplanar distance of 1.63±0.03 Å. Strain analysis, involving a comparison with the equilibrium structure of bulk ${\mathrm{Pt}}_{0.5}$ ${\mathrm{Fe}}_{0.5}$, shows that this result implies that in thin ${\mathrm{Pt}}_{0.5}$ ${\mathrm{Fe}}_{0.5}$ films, Poisson’s ratio approximates the value for the limit of elastic softening. The values of the critical thickness for the formation of misfit dislocations are estimated for both the elemental and the alloy overlayers.