K.F. Badawi

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.

Poisson’s ratio measurement in tungsten thin films combining an x-ray diffractometer with in situ tensile tester

A direct determination of the Poisson’s ratio in 150 nm polycrystalline tungsten thin films deposited by ion-beam sputtering on Duralumin substrates has been performed by combining x-ray diffraction measurements with in situ traction on the sample. X-ray diffraction experiments using the sin2 ψ method have been done at LURE, the French synchrotron facility (Orsay, France) on a four-circle diffractometer. The method described in this letter allows us to extract in a simple way and with a good precision the Poisson’s ratio of thin films on substrates from the evolution of the sin2 ψ curves as a function of applied strains. In the case of tungsten thin film, the value obtained is close to the bulk material one.

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.

Residual stresses and microstructure in tungsten thin films analyzed by x‐ray diffraction‐evolution under ion irradiation

Microstructure and residual stresses have been studied in 100 nm tungsten thin films deposited by ion beam sputtering on silicon substrates. Residual stresses, stress‐free lattice parameter, crystal microdistortions, and average length of the coherently diffracting domains have been deduced from x‐ray diffraction measurements. The as‐deposited film is strongly compressed (−5.2 GPa) and its microstructure is very far from the bulk tungsten one: the coherently diffracting domain size is nanometric (about 5 nm), the stress‐free lattice parameter is larger than the bulk one (about 0.6%), and microdistortions are considerable (0.6%). The ‘‘atomic peening’’ model is proposed to explain the mechanical state of these films. Diffraction analysis, correlated with impurity concentration measurement, evidences the main role played by backscattered Ar ions in stress genesis. Nevertheless, the contribution of the most energetic W particles to the stress generation process cannot be neglected. We have equally studied Ar...

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.

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.

X-ray diffraction study of residual stress modification in Cu/W superlattices irradiated by light and heavy ions

Abstract The effect of low temperature ion irradiation on the residual stress state was studied as a function of the ion fluence in Cu/W superlatices prepared by ion beam sputtering. The residual stress tensor in tungsten layers is completely determined from X-ray diffraction data using the “sin2ψ method”. In the as-prepared state, the Cu/W superlattices are strongly strained, and we find in-plane compressive stresses as high as 6.4 GPa in tungsten layers. Relaxation of the stress state is observed after low temperature ion irradiation with increasing dose. This phenomenon is almost complete for doses as low as 0.1–0.2 dpa, and appears related to atomic rearrangement in the elemental layers rather than interfacial mixing. The role of the incident particle mass is also evidenced. Per dpa, heavy ion irradiation (Kr) induces the strain relaxation more quickly than light ions (He).

Influence of microstructure on residual stress in tungsten thin films analyzed by X-ray diffraction

Abstract Microstructure and residual stresses have been studied in 100 nm thin tungsten films deposited by ion beam sputtering on silicon substrates. Residual stresses, the stress-free lattice parameter, crystal microdistortions and the average length of the coherently diffracting domains (CDD) have been measured by X-ray diffraction. The as-deposited film is strongly compressed (−5.2 GPa) and its microstructure is very far from that of bulk tungsten: the size of the CDD is nanometric (about 5 nm), the stress-free lattice parameter is larger than in the bulk (about 0.6%) and microdistortions are considerable (0.6%). Our diffraction data are in agreement with the “atomic peening” model usually admitted to explain the compressive stresses in sputtered films. These features are also confirmed by irradiations with Ar+ ions (340 keV). They induce simultaneously a total stress relaxation, a return of the stress-free lattice parameter to the bulk value and a strong decrease of the microdistortions.