Microstructure and Mechanical Properties of Nanolayered TiN/Cu Thin Films
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Microstructure and Mechanical Properties of Nanolayered TiN/Cu Thin Films Y.Y. Tse, G. Abadias, A. Michel, C. Tromas and M. Jaouen Laboratoire de Métallurgie Physique, UMR 6630 CNRS, Université de Poitiers, SP2MI, Téléport 2, BP 30179, 86962 Futuroscope-Chasseneuil cedex, France ABSTRACT Structural and mechanical properties of nanoscale TiN/Cu multilayers grown by dual ion beam sputtering with bilayer periods (Λ) ranging from 2.5 to 50 nm were studied. Both lowangle and high-angle X-ray diffraction (XRD) experiments have been employed to globally characterize the multilayers structure. The microstructure of the multilayers has been scrutinized by high resolution transmission electron microscopy (HRTEM). The effects of interface and bilayer thickness on hardness were investigated by depth-sensing nanoindentation technique. A small hardness increase with decreasing periodicity of the multilayers has been observed. The relationship between the hc/T ratio (hc is the contact depth and T is the total film thickness) and the hardness is established. The correlation between the microstructure and hardness is discussed. INTRODUCTION As the mechanical properties of monolithic films showed their limitation, nanometer scale composite system combining different element properties are now widely used for some tailorable and unique applications [1]. As the deposition techniques become more sophisticated, it is possible to grow hard/superhard multilayers in the form of metal/metal, nitride/nitride or nitride/refractory metal with bilayer thickness (Λ) in nanometer ranges [2]. These nanostructure composite materials exhibit large hardness enhancement with respect to the expected value obtained from the rule of mixture [3,4]. Various models have been proposed to account for the hardness enhancement by considering the lattice mismatch, shear moduli and effect of different dislocation slip systems across interfaces [3-5]. However, most of the literature studies, though shedding some lights on a basic understanding of plasticity in nanoscale films, provide limited quantitative analysis on the “hard nitride”/ “soft metal” multilayer systems. As part of a systematic study of mechanical properties of nanocomposites, we report recent results on a composite system which comprises a hard nitride component (TiN) and a very soft metal component (Cu). In contrast to other multilayers studied in the literature, a very large shear modulus difference (GTiN ~192 GPa, GCu ~58 GPa) and lattice mismatch (15.9%) between TiN and Cu are noticed. In order to understand nanocomposite microstructure evolution, mechanical properties and particularly their inter-relationship, efforts were made in detailed characterization of the TiN/Cu multilayers with different periodical thickness. EXPERIMENTAL PROCEDURE TiN/Cu multilayers were deposited using dual ion beam sputtering technique by sputtering pure Cu (99.9%) and Ti (99.99%) targets. Depositions were done in an ultrahigh vacuum (1. Figure 3(b) shows that the indentation contact depth hcmax is almost li
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