Vue d'ensemble sur la preparation, la caracterisation, les proprietes de transport et les proprietes magnetiques des superreseaux

Artificial metallic superlattices

The extensive use of thin films in the manufacture of microelectronic devices and for protection against wear and corrosion has stimulated considerable interest in their mechanical properties. In t...

Mechanical testing of thin films

A method has been developed to produce composition-modulated alloys by electrodeposition. The method was demonstrated for the copper-nickel couple. Salts of the two component metals are dissolved in a common electrolyte and the potential is alternately pulsed for fixed durations between values above and below the reduction potential of the less noble component. Co-deposition of the nobler metal into the other metal layer is diminished by setting unfavourable diffusion conditions during the more cathodic pulse. Modulation was achieved down to 0.8 nm thick layers. The resulting composition-modulated alloys were analysed by Auger spectroscopy and X-ray diffraction.

Formation of composition-modulated alloys by electrodeposition

The biaxial elastic modulus Y[111] has been measured by bulge testing in Ag‐Pd and Cu‐Au thin foils containing one‐dimensional composition modulations with wavelengths ranging from 0.9 to 5.5 nm. For the Ag‐Pd foils having wavelengths of 2.0–3.0 nm, the modulus was up to 2.3 times greater than that of homogeneous foils of the same average composition. The increase was found to be proportional to the square of the amplitude of the modulation. In foils containing modulations of wavelengths less than 2.0 nm or greater than 3.0 nm, the modulus was the same as that of homogeneous foils. It was observed that the deformation was elastic but non‐Hookean. For the Cu‐Au modulated foils no modulus enhancement was observed: The modulus for any wavelength was in good agreement with that calculated from the bulk elastic constants.

Elastic modulus in composition‐modulated silver‐palladium and copper‐gold foils

The mechanical properties of compositionally modulated Au-Ni films were investigated by submicrometer depth-sensing indentation and by deflection of micrometer-scale cantilever beams. Films prepared by sputter deposition with composition wavelengths between 0.9 and 4.0 nm were investigated. Strength was found to be high and invariant with composition wavelength. Experimental and data analysis methods were developed to provide more accurate and precise measurements of elastic stiffness. Large enhancements in stiffness (the “supermodulus effect”) were not observed. Rather, relatively small but significant minima were observed at a composition wavelength of about 1.6 nm by both techniques. These variations were found to be strongly correlated with variations in the average lattice parameter normal to the plane of the film. Both structural and mechanical property variations are consistent with a simple model in which the film consists of bulk-like Au and Ni layers with interfaces of constant thickness.

Mechanical properties of compositionally modulated au-ni thin films : nanoindentation and microcantilever deflection experiments

Films with modulated composition 8‐A Cu/8‐A Ni show an increase in the Young’s and torsional moduli of a factor of 2, relative to bulk or longer‐wavelength samples. The film structure is found to be highly textured with coherent lamella for the short‐wavelength‐enhanced moduli samples, but becomes more random with the probable introduction of misfit dislocations at longer wavelengths. The moduli results support the previous findings of Tsakalakos and Hilliard.

J. T. Krause

Papers

Enhanced elastic moduli in Cu‐Ni films with compositional modulation