Gd silicides formation: heat treatment of coadsorbed Si and Gd ultrathin films on a W(1 1 1) surface

Effect of heat treatment of Si and Gd submonolayer coverages, coadsorbed on the W(1 1 1) plane at room temperature (RT), on the formation of the Gd silicides of various stoichiometry has been investigated using field emission technique. Stoichiometry of the Gd silicides produced is found to depend on the ratio of codeposited species. The Gd silicides formation was checked via the work function measurements of the adsystem during annealing. A manifestation of the work function invariability in a wide temperature range gives evidence to the formation of stable compounds that can be attributed exclusively to the Gd silicides in our case. Three types of the Gd-silicides were found and identified as corresponding to the Gd rich silicides with the work function ϕ=3.05 eV, the monosilicides with ϕ=3.70 eV and the Si-rich silicides with ϕ=4.10 eV. All the Gd silicides produced were stable within the same temperature range 1200–1850 K. The Gd silicides formation was also observable in the changes of the Fowler–Nordheim (FN) preexponential that, in addition, reflected the metallic character of their conductivity.