Size effects on the Mechanical Behavior of Nanometric W/Cu Multilayers
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1086-U04-04
Size effects on the mechanical behavior of nanometric W/Cu multilayers Baptiste Girault, Guillaume Geandier, Dominique Eyidi, Pierre-Olivier Renault, Eric Le Bourhis, and Philippe Goudeau PhyMat - UMR 6630, University of Poitiers, Boulevard Marie et Pierre Curie, Téléport 2, Poitiers, 86962, France
ABSTRACT The mechanical behavior of nanostructured W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and GrazingIncidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. INTRODUCTION Nanometer scaled materials meet non negligible surface contribution yielding deviations from mechanical bulk materials behavior. Stratified samples have attracted much attention since one dimension can be tailored down to the nano-scale, leading to novel electronic, magnetic, optical and mechanical applications. Despite the number of studies devoted to length scale dependence of strength and deformation mechanisms in nano-scale multilayers [1-6], few of these focus on the mechanical response in the elastic domain. Elastic constants analysis in nanocrystalline metallic thin films and multilayers by means of a method combining X-ray diffraction and tensile testing has been a constant challenge in our laboratory for several years [7-10]. The present paper focuses on experiments involving stratified W/Cu samples with tungsten layer thicknesses ranging from 10.8 nm down to 1.5 nm and presenting constant average copper layer thickness of 0.2 nm. X-ray measurements were performed at the European Synchrotron Radiation Facility (Grenoble, France). EXPERIMENTS Specimen preparation W/Cu multilayers were deposited by ion-beam sputtering in a NORDIKO 3000 device at room temperature, tungsten being the first deposited layer, on 127.5 µm thick polyimide (Kapton®) dogbone foils and on 200 µm and 600 µm thick naturally oxidized Si (001) wafers. The gauge part of dogbone samples has a size of 6 × 15 mm². Sample characteristic data, including the number of (W,Cu) layer pairs and the total film thickness of each specimen, are given in Table I. The film mean residual stresses were evaluated using the curvature method with the dedicated
200 µm Si cantilevers. The global stress states set in thin films were strongly compressive. X-ray diffraction pole figures measurements showed that W layers exhibit both and fiber-texture [11]. X-ray reflectometry measurements combined with atomic concentration determined by ED
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