Mechanical Properties of Compositionally Modulated Au-Ni thin films using Indentation and Microbeam Deflection Techniques

The “supermodulus effect” has been reported as an anomalous increase of as much as several hundred percent in the elastic moduli of compositionally-modulated thin metal films in a narrow range of modulation wavelength. The direct measurement of this effect has, however, been limited due to the very small dimensions of the test material. The mechanical properties of compositionally-modulated Au-Ni thin films (one of the first systems in which the supermodulus effect was reported) were studied on their substrates by indentation and microbeam-deflection techniques using a Nanoindenter. The films were fabricated by alternately sputtering Au and Ni onto [100] Si substrates for the indentation tests and onto prefabricated SiO 2 cantilever beams with an initial Cr layer (for adhesion) for the beam deflection tests. All of the films have strong [111] textures and exhibit the structural characteristics of the films for which the modulus enhancement was reported. In particular, an increase in the average lattice parameter normal to the plane of the film over a narrow range of modulation wavelengths near 2 nm was noted. The modulation wavelengths range from 0.8 to 4.5 nm. The results from both indentation and microbeam deflection tests reveal no unusual plastic or elastic properties in these samples.