P. Villain

Measuring thin film and multilayer elastic constants by coupling in situ tensile testing with x-ray diffraction

A direct determination of the Young’s modulus and the Poisson’s ratio in a 140 nm polycrystalline tungsten thin film deposited by ion-beam sputtering on a polyimide substrate has been performed by coupling x-ray diffraction measurements with in situ tensile testing. The method described in this article to extract the Young’s modulus of thin films from the evolution of the sin2 ψ curves as a function of applied load only requires to know the substrate Young’s modulus. The determination of the thin film Poisson’s ratio can be realized without knowing any of the substrate elastic constants. In the case of the tungsten thin film, the obtained Young’s modulus was close to the bulk material one whereas the Poisson’s ratio was significantly larger than the bulk one.

Size effect on intragranular elastic constants in thin tungsten films

The size effect on the elastic constants of nanocrystalline tungsten has been investigated in the case of W/Cu multilayers with two modulation wavelengths (3.1 and 24.0 nm). Tungsten Young’s modulus and Poisson’s ratio have been measured thanks to a technique coupling x-ray diffraction with in situ tensile testing. It is demonstrated that the in-grain thin film elastic constants are highly microstructure—sensitive: in the “3.1 nm” multilayer, tungsten Poisson’s ratio is larger than the bulk one while it is smaller in the “24.0 nm” multilayer; a softening of tungsten Young’s modulus is evidenced in the case of the specimen with the smallest period.

Measurement of the elastic constants of textured anisotropic thin films from x-ray diffraction data

The elastic constants (compliances sij) of a textured anisotropic thin film deposited on a substrate have been determined. Using x-ray diffraction to measure the intragranular strain and a tensile machine to deform in situ the samples, an analytical method is described and has been developed for fiber textured thin films. The determination of thin film compliances only requires the knowledge of the substrate elastic constants. In the case of a 260-nm-thin gold film, the compliances were found to be slightly different from the corresponding bulk material ones.

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

Abstract In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin 2 ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.

Characterization of thin film elastic properties using X-ray diffraction and mechanical methods: application to polycrystalline stainless steel

The Youngs modulus and Poissons ratio of reduced thickness layers are generally unknown whereas simulation of mechanical behavior of thin film/substrate systems or stress determination by X-ray diffraction cannot be done in an accurate way without the knowledge of these values. In this paper, we present three types of experiments which are used in our laboratory for determining elastic constants in polycrystalline thin films elaborated by ion beam sputtering: A vibrating reed device, X-ray tensile testing and AFM buckling geometry analysis. Results obtained for metallic 304L stainless steel thin films are given.

Mesoscale x-ray diffraction measurement of stress relaxation associated with buckling in compressed thin films

Compressed thin films deposited on substrates may buckle depending on the geometrical and mechanical properties of the film/substrate set. Until recently, the small dimensions of the buckling have prevented measurements of their local in plane internal stress distribution. Using a scanning x-ray microdiffraction technique developed at a third generation x-ray synchrotron source, we obtained thin film internal stress maps for circular blisters and telephone chord buckling with micrometric spatial resolution. A fair agreement was found between the film delamination topology observed by optical microscopy and the measured stress maps. We evidenced residual stress relaxation associated with the film buckling: the top is essentially stress free while adherent region exhibits large compressive stresses.

X-Ray diffraction measurement of the Poisson's ratio in Mo sublayers of Ni/Mo multilayers

Elasticity in low dimensional systems is still misunderstood although numerous experimental and theoretical studies on this subject have been done since the 1990s. Recently, we developed a new X-ray diffraction method based on in situ tensile deformation of the film/substrate set to investigate the elastic properties of both the film and the substrate and in particular to extract in a simple way the Poissons ratio of the film. This method has been applied to study a polycrystalline stratified system composed of 13 bilayers (15 nm nickel and 8 nm molybdenum thick layers for each bilayer), deposited on a Duralumin substrate. The Mo Poissons ratio has been determined; its value is close to the bulk one for the studied thickness. In addition, the applied strain transmission through the film/substrate interface has been analysed.

Strains, stresses and elastic properties in polycrystalline metallic thin films: in situ deformation combined with x-ray diffraction and simulation experiments

X-ray diffraction is used in combination with tensile testing for measuring elastic properties of metallic thin films. Size effect, elastic anisotropy and grain morphologies are considered in all these experiments and supported by different kind of numerical simulations operating at different length scales. Such instrumental studies are time consuming even if synchrotron sources are used. New experiments are under progress for reducing acquisition data and improving precision on strain measurements. After introducing briefly the main principles and results of our techniques, first promising measurements on nanometric W/Cu multilayers using 2D CCD detectors and high monochromatic flux at the Advanced Light Source Berkeley (USA) on beam line 11.3.1 are presented. In addition, simulation experiments for analyzing elasticity in textured gold film are discussed.

D-78 Elastic Properties of Nano-Structured Thin Films: Characterization and Modeling

different microstructures are elaborated, the microstructure of which being characterized by TEM (grain shape, layer thickness …), X-ray reflectometry (multilayer period, density) and X-ray diffraction (XRD: crystallographic texture, layer thicknesses). These films are supported by a polyimide foil substrate. Films mechanical response is characterized experimentally by XRD based in-situ techniques [2] to assess the orientation and depth dependences of elastic strain and stress. Results are interpreted by an appropriated mechanical modeling accounting for the material microstructure, based on homogenization schemes. An in-situ biaxial tensile apparatus is currently developed in the frame work of the French Agency for Research (Cmonano project, ANR-05-PNANO-069) and will be installed at Diffabs beam line of the new French synchrotron SOLEIL. This machine allows exploring many different configurations of

X-ray Diffraction Study of the Mechanical Elastic Properties of Nanometric W/Cu Multilayers

The mechanical behavior of W/Cu multilayers with a period of 24 nm and a 1/3 W/Cu thickness ratio prepared by magnetron sputtering was analyzed using a method combining X-ray diffraction and tensile testing. Tests were performed both with a conventional and a synchrotron light source to analyze the elastic response of the system. Comparison between the strain-load curves obtained in both experimental conditions and estimated curves clearly shows that high quality synchrotron measurements are a preliminary condition for size-effect studies. Moreover, cyclic tests were used to determine the elastic domain of each material and compare their mechanical responses. Plastic strain was observed in copper before in tungsten layers in accordance with the mechanical behavior of their bulk counterparts.