engleski

STRUCTURAL STUDY OF Ni-Nb THIN FILMS

STRUCTURAL STUDY OF Ni-Nb THIN FILMS Radić, N1, Dubček, P1, Bernstorff, S3, Skoko, Ž 2, Ristić, M1, Siketić, Z1 1 Rudjer Boskovic Institute, Bijenicka 54, 10000 Zagreb, Croatia 2 Faculty of Sciences, Physics Department, Bijenicka 32, 10000 Zagreb, Croatia 3 Sincrotrone Trieste, Strada Statale 14, km163.5, 34149 Basovizza, Italy Ni-Nb thin films (500 nm) have been prepared in a full range of compositions (pure Ni - pure Nb) by magnetron codeposition onto various substrates. The chemical compositions of the alloys have been determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), while the structure of the as-deposited films has been determined by X-Ray Diffraction. It has been found that the glass-forming range (25-85 at.% Ni) conforms very well with the glass forming ability estimated from molecular dynamics simulations and Miedema's theory. Below 10 at.% Nb content, the prepared films are fcc crystalline Ni(Nb) solid solutions. The Ni(Nb) (nano)crystallites (20-30 nm) are preferentially (111) oriented in the direction perpendicular to the film plane. Grazing incidence small angle x-ray scattering (GISAXS) results indicate that the surface contributions dominate in the GISAXS patterns from the nickel rich samples. Upon increasing the Nb content of the samples, the sample surfaces become smoother, and the GISAXS patterns become better defined. In the glass-forming range, the surface structure becomes island-like, with a narrow size distribution both vertically and horizontally. When scattering pattern taken at wider angles are compared to those taken at the critical angle, the bulk contribution scattering can also be deduced. The sizes of bulk features are fairly similar for most concentrations. However, the values that stand out are in the glass-forming range, as well as with 90%Ni content, where the bulk features appear to be 50% bigger. The GISAXS findings have also been confronted with the images obtained by scanning electron microscopy from selected samples.

Ni-Nb alloys; thin films; GISAXS

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