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Brillouin light scattering was used to measure the elastic properties of a set of Langmuir–Blodgett films with varying thickness. Samples are constituted of stacks from 3 to 75 monolayers of a octabutoxyphthalocyanine copper derivative, deposited on Si substrates by the Langmuir–Blodgett (LB) technique. Due to the strong contrast in the elastic properties of the organic films and the substrate, it is shown that an elastic anomaly, if any, should be revealed by the Rayleigh mode and the first Sezawa mode which both strongly depend on the value of C[sub 44]. Rayleigh and Sezawa dispersion curves are computed assuming that the elastic constants do not depend on the number of individual monolayers in the LB film. Within the accuracy of the experimental data, the theory well reproduces the trend of the effective velocities, showing so that the elastic properties of the material do not depend on the number of molecular monolayers in the stack. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structure, phase stability, and mechanical properties of ternary alloys of the Zr-Ta-N system are investigated by combining thin-film growth and ab initio calculations. Zr1-xTaxN films with 0 ⩽ x ⩽ 1 were deposited by reactive magnetron cosputtering in Ar + N2 plasma discharge and their structural properties characterized by x-ray diffraction. We considered both ordered and disordered alloys, using supercells and special quasirandom structure approaches, to account for different possible metal atom distributions on the cation sublattice. Density functional theory within the generalized gradient approximation was employed to calculate the electronic structure as well as predict the evolution of the lattice parameter and key mechanical properties, including single-crystal elastic constants and polycrystalline elastic moduli, of ternary Zr1-xTaxN compounds with cubic rocksalt structure. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. The thermal stability of these Zr1-xTaxN films is also studied, based on their structural and mechanical response upon vacuum annealing at 850 °C for 3 h. Our findings demonstrate that Zr1-xTaxN alloys with Ta fraction 0.51 ⩽ x ⩽ 0.78 exhibit enhanced toughness, while retaining high hardness ∼30 GPa, as a result of increased valence electron concentration and phase stability tuning. Calculations performed for disordered or ordered structures both lead to the same conclusion regarding the mechanical behavior of these nitride alloys, in agreement with recent literature findings [H. Kindlund, D. G. Sangiovanni, L. Martinez-de-Olcoz, J. Lu, J. Jensen, J. Birch, I. Petrov, J. E. Greene, V. Chirita, and L. Hultman, APL Materials 1, 042104 (2013)]. [ABSTRACT FROM AUTHOR]

We present a detailed experimental study on Mo1-xSix thin films, an archetypal alloy system combining metallic and semiconductor materials. The correlations between structure and elastic response are comprehensively investigated. We focus on assessing trends for understanding the evolution of elastic properties upon Si alloying in relation to the structural state (crystalline vs amorphous), bonding character (metallic vs covalent), and local atomic environment. By combining picosecond ultrasonics and Brillouin light scattering techniques, a complete set of effective elastic constants and mechanical moduli (B, G, E) is provided in the whole compositional range, covering bcc solid solutions (x<0.20) and the amorphous phase (0.20

Abstract: The composition-dependence of the structure and elastic properties of ternary Ti1– x Zr x N alloys is systematically investigated by combining thin film growth and ab initio calculations. Single-phase Ti1– x Zr x N thin films (0⩽ x ⩽1) with a rocksalt structure have been deposited using dc reactive magnetron sputtering at T s =300°C in Ar/N2 plasma discharges. The structure, stress state and phase stability upon thermal annealing were studied by X-ray diffraction (XRD), while the acoustic and elastic properties were measured using Brillouin light spectroscopy, picosecond ultrasonics and nanoindentation. First-principles pseudopotential calculations of the total energy, lattice constants, bulk modulus, and single-crystal elastic constants Cij for several cubic ordered structures of Ti1– x Zr x N alloys were also carried out. The positive values of the computed formation energies indicate that the homogeneous Ti1– x Zr x N alloys can be only stabilized at high temperatures. However, the magnetron-sputtered thin films were found to retain their as-grown single-phase cubic structure during post-deposition annealing at 850°C for 3h. The calculated equilibrium lattice parameters are in good agreement with the stress-free lattice parameters a 0 determined experimentally from XRD using the sin2ψ method: they both exhibit a positive deviation from Vegard-like linear interpolation. The calculated bulk modulus, elastic constants and Poisson’s ratio gradually decrease from TiN to ZrN. These computed values were used to interpret the experimentally derived elastic constants and Young’s modulus as functions of composition. [Copyright &y& Elsevier]