Characterization of thinNb3Sn diffusion layers on Nb(110): Low-energy electron-diffraction and photoemission studies

We have carried out low-energy electron-diffraction and ultraviolet photoemission spectroscopy studies of the surface structures formed by annealing Sn overlayers deposited on Nb(110) substrates at room temperature. In addition to the usual ring patterns observed by electron diffraction, we observe a preferred azimuthal orientation with ${\mathrm{Nb}}_3$Sn [100] parallel to Nb [111] in the surface plane. The photoemission results show three regimes of Sn coverage extending from submonolayer Sn structures to the limit of thick islands of Sn, the latter being a prerequisite to forming the $A15$, ${\mathrm{Nb}}_3$Sn structure. The contribution of the $\mathrm{Sn}4p$ states to the electronic structure is followed as a function of Sn coverage. The evolution of the photoemission spectra as a function of sample annealing shows the trend through the $A15$ structure to the relatively inert $p(1\mathrm{}\times 1)$ phase of Sn on Nb.