Thin films of completely immiscible Ag-W system have been prepared in a wide range of composition by codeposition of pure silver and pure tungsten sputtered by two independently controlled magnetron sources. Deposition rate onto substrates (glass, alumina, sapphire, mono-Si) at room temperature was about 0,33 nm/s, and the final film thickness was about 500 nm. The effects of working gas pressure, and of oxygen or aluminum incorporation upon the film structure have been examined.
The chemical composition of the prepared films has been determined by the RBS technique. The structure of prepared films was examined by the XRD, GISAXS and SEM methods. No completely amorphous films have been obtained in the composition range Ag94W6-Ag12W88. A supersaturated solid solution Al(W) with the fcc structure is formed with <30 at.% W, while a bcc solid solution is formed for higher tungsten content. A nanocrystalline bcc phase (grain size of about 5 nm) has been obtained in the Ag-W alloys with 30-50 at.% W content. The interplanar (111) distance in the nanocrystalline alloys increases upon approaching structural "switching" composition from the W-rich side. The SEM analysis reveals a significant variation across the examined composition range: at the fcc crystalline range boundary a densely packed film of rather uniformly sized 20-30 nm particles is sparsely dotted with the well-developed several hundred nanometers large crystalline particles. On the W-rich crystalline side the grass-like surface of the film is decorated on top by 20 nm sized particles at about 50-100 nm mutual distance. In the XRD-nanocrystalline range the bulk of the film is formed of densely packed disc-like particles covered on top by few tens of nanometers sized crystalline-like particles. General trend from the Ag-rich end towards W-rich end for the bulk of the film is decrease in compactness, while particles atop the film surface decreases in size from several hundreds nanometers to about ten nanometers.
The GISAXS results refer to the inhomogeneities in electron density of about few nm in size, presumably corresponding to the intercrystalline matter/voids. The incorporation of oxygen into the film decreases somewhat the average grain size, producing no completely amorphous phase, however.
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