Philippe Djemia

Abstract: First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants of Ti1-xZrxN (0 � x � 1) alloys were carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys. For the exchange-correlation potential we used both the local density (LDA) and the generalized gradient methods (GGA). The calculated equilibrium lattice parameters exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter, while the calculated single-crystal stiffnesses, namely C11, C12 and C44, gradually decrease from TiN to ZrN. In a second stage, in the frame of anisotropic elasticity, we have estimated by homogenization methods the averaged stiffnesses <Cij>, direction dependent Young's moduli and Poisson's ratios of polycrystalline Ti1-xZrxN (0 � x � 1) alloys considering a {111}-fiber texture.

Abstract: The lattice dynamics and the elastic properties of the ternary AlAsxSb1-x alloy have been studied using the density-functional perturbation theory within the local density approximation and employing the virtual-crystal approximation. We study the variation of the optical phonon frequencies (TO and LO), the high-frequency (epsilon) and static (epsilon 0) dielectric coefficients, the dynamic effective charge (Z*) and the elastic constants (C11, C12, C44) as a function of the composition (x) and the pressure. We have also predicted the behavior of the optical and acoustical phonons with composition x at the X and L high symmetry points under pressure and determined the Gruneisen parameter. We have found that no mechanical instabilities are associated with the structural transition at high pressures for all compositions.

Abstract: Elastic properties of Mo1 xa0;� xa0;xSix alloy films with 0 xa0;� xa0;x xa0;� xa0;1 have been investigated by the Brillouin light scattering technique thanks to the analysis of the surface acoustic waves in the film on substrate: the so-called Rayleigh surface wave and the Sezawa waves. A transition from crystalline to amorphous state is observed for a Si content, x xa0;= xa0;0.19. This transition is accompanied by different modifications of the elastic constants, namely, C11, C33, C13 and C44 that are necessary with C12 to define the effective hexagonal symmetry for the textured <110> polycrystalline alloys. A pronounced softening of the shear elastic C44 constant is observed, from 110 to 60 xa0;GPa when x varies from 0 to the critical threshold composition x xa0;= xa0;0.19. The longitudinal C33 constant estimated in this work from the BLS measurements shows also a softening from 425 to 315 xa0;GPa. An intrinsic consequence of the high supersaturation of MoSi alloys is the development of an important lattice instability. In the amorphous state, the evolution of the elastic properties, that can be defined by the two independent constants C11 and C44 xa0;= xa0;(C11 xa0;� xa0;C12)/2, exhibits two distinct behaviors depending on the electronic properties and the interatomic bonding of the amorphous alloys.

Abstract: In this paper, we compare the electromechanical properties of tetragonal single domain PZN-12%PT single crystals obtained by different methods: resonance-antiresonance method, Brillouin scattering, and resonant ultrasound spectroscopy. The agreement between the different measurements is found satisfactory for many elastic constants within experimental uncertainties. Differences are notable for the elastic constants associated to the propagation of shear waves (c66E and c44E). This can be accounted for by imperfections of the sample in acoustic spectroscopy and specific difficulties of shear resonators used for the resonance method. Strong discrepancies are noted for the hardened elastic constant c33D associated to longitudinal waves propagating along the polarization direction; we suggest this can arise from a frequency dependence of the dielectric constant.

Abstract: Ferromagnetic films with perpendicular anisotropy and above a critical thickness exhibit weak stripe magnetic domains. The dynamic response of such systems with inhomogeneous state under moderate applied field can then be a probe of the local as of the macroscopic magnetization evolution. The static properties of Permalloy (Py) films of different thicknesses are obtained by VSM and MFM. Then the dynamic response is both investigated with a micro-stripe line device (FMR) and by Brillouin light scattering (BLS). For thick Py films three modes are observed below saturation which merge into a single one in the staturated state. Micromagnetic simulations have been performed to get the various resonance frequencies and the spatial distribution of the modulus of the dynamic magnetization for each mode. BLS spectra also show frequency multi-modes (at low q) in the non saturated state.

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Abstract: Synchrotron x-ray radiation was used for in situ strain measurements during uniaxial tests on polymer substrates coated by a metallic gold film 400 nm thick deposited without interlayer or surface treatment. X-ray diffraction allowed capturing both components elastic strains and determining how these were partitioned between the metallic film and the polymeric substrate. For strains below 0.8%, deformation is continuous through the metal-polymer interface while above, the onset of plasticity in the metallic film induces a shift between film and substrate elastic strains.

Abstract: Performing a complete in-situ strain measurement of polycrystalline thin films using X-ray diffraction is time consuming with most standard diffraction beamlines at synchrotron facilities and not realistic with laboratory diffractometers. Two dimensional detection is shown to enable relatively fast and reliable X-ray strain measurements during continuous in-situ tensile testing of metallic films deposited on polyimide substrates. We show in this paper the advantages to perform this kind of measurements as compared to those with punctual detection.

Abstract: We have performed strip line ferromagnetic resonance on weak stripe domains in permalloy layers. We used Thiele equation of motion to interprete our experimental data : the lowest frequency mode corresponds to the motion of vortices inside the layer, its frequency is evaluated through the relation omega = k/G where G is the gyrovector magnitude and k is a stiffness which mainly depends on demagnetizing effects.

Abstract: Elastic properties of non-textured and 1 1 1-fiber-textured gold thin films were investigated experimentally by several complementary techniques, namely in situ tensile testing under X-ray diffraction (XRD), nanoindentation and Brillouin light scattering (BLS). Specimens were probed along different directions to reveal the strong effects of elastic anisotropy at the (local) grain and (global) film scales. XRD allows the investigation of both local and global anisotropies, while BLS and nanoindentation are limited to global analyses. A micromechanical model, based on the self-consistent scheme, and accounting for the actual microstructure of the films, is applied to interpret experimental data. Although different types of elastic constants can be determined with the used experimental techniques (static/dynamic, local/global), a good agreement is obtained, showing that comparison of these techniques is feasible when carried out carefully. In particular, the use of a micromechanical model to estimate the effects of the local elastic anisotropy at the film scale is unavoidable. The presented results show that XRD, BLS and nanoindentation should capture anisotropic texture effects on elastic constants measurements for materials with a Zener anisotropy index larger than 2. Conversely, the actual texture of a given specimen should be taken into account for a proper analysis of elastic constants measurements using those three experimental techniques. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Abstract: Behaviour of magnetic excitations in the Damon-Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO2)(100-x)Co-x (50% at <x<80% at) films has been studied by Brillouin light scattering (BLS). It has been shown that it is the structure of Stokes/anti-Stokes BLS lines in the DE geometry that allows reliable identification of dipole-exchange spin waves (SW) and numerical estimation of the value of the effective exchange constant A(eff) of a super-ferromagnetic nano-granular sample (x = 80% at). (C) 2008 Elsevier B.V. All rights reserved.

Abstract: The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (omega(TO) and omega(LO)), the high-frequency dielectric coefficient (epsilon(infinity)) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the omega(TO) and omega(LO) follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained epsilon(infinity) and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.

Abstract: The lattice dynamics and elastic properties of the ternary AgBr1-xClx alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (omega(TO) and omega(LO)) and of the acoustical phonon frequencies (omega(TA) and omega(LA)), the high-frequency dielectric coefficient (epsilon(infinity)), the dynamic effective charge (Z*) and the elastic constants (C-11, C-12, C-44) as a function of the composition (x). We find that the phonon frequencies as well as the elastic constants follow a quadratic law in x and agree well with the available experimental results. The elastic constant tensors for simple cubic 8-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA and experiments. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Dynamic magnetic properties of arrays of Ni nanorods with a low aspect ratio have been investigated. It has been shown that the spectra of spin-wave resonances localized on nanorods with a low aspect ratio typically feature the presence of zones with high density of states resulting in a characteristic two-peak pattern of Stokes and anti-Stokes lines of magneto-optical (MO) Brillouin light scattering with pronounced Stokes-anti-Stokes (S-AS) asymmetry. A simple theoretical model based on the analysis of the elliptic character of the polarization of the optical wave interacting with a dipole magnetostatic wave has been proposed. It has been shown that the S-AS asymmetry is due entirely to the asymmetry of the MO interaction efficiency with respect to time reversal of the magnetic precession in a magnon.

Abstract: The lattice dynamics and elastic properties of the ternary ZnxCd1-xSe alloy have been studied using first-principle calculations. These are done using the density-functional perturbation theory (DFPT) within local density approximation (LDA) and employing virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (omega(TO) and omega(LO)), the high-frequency dielectric coefficient (epsilon(infinity)), the dynamic effective charge (Z*) and the elastic constants (C-11, C-12, C-44) as a function of the composition (x). We found that the omega(TO) and omega(LO) follow a quadratic law in x and agree well with the experiment. The obtained epsilon(infinity), Z*, C-11, C-12 and C-44 have a quadratic form with x. The elastic constant tensors for simple cubic eight-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA.

Abstract: We report on the first measurements of the physico-mechanical properties of the raffia textilis fiber. This fiber is the epidermis of the leaflet and is used to fabricate many ethnographical items. Scanning electron microscopy reveals a layered structure: a top layer with a tile-like structure, and a bottom layer with a honeycomb-like structure. X-ray diffraction and FTIR-ATR show the presence of cellulose I-beta with a crystallinity index of 64%. Tensile tests give a Young�s modulus of 30 GPa, a tensile strength of 500 +/- 97 MPa, and a total elongation between 2% and 4%. The fiber density is 0.75 +/- 0.07, conferring to it the highest known specific mechanical properties among all studied raw vegetable fibers. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: The effect of structural and chemical disorder on magnetism of Mn-implanted 3C-SiC epilayer on Si(100) is investigated experimentally using Rutherford backscattering channeling spectroscopy (RBS/C), x-ray diffraction (XRD), micro-Raman spectroscopy (mu RS), and magnetometry, and theoretically using ab initio calculations. A single 3C-SiC epilayer on Si(001) was implanted at room temperature (RT) with Mn ions at 80 keV and at a dose of 5x10(15) cm(-2). RBS data show the formation of a highly disordered implanted layer of similar to 45 nm with a peak Mn atomic concentration of similar to 1.8% randomly distributed, in agreement with the stopping and range of ions in matter (SRIM) simulation. The experimental results of magnetic moment per Mn are interpreted by assuming that the implanted layer consists of two respective main regions, C-rich and Si-rich regions, as reflected by the presence of a graphitic phase, in which the local atomic environment of Mn is essentially C. Annealing seems to favor Mn substitution into Si sites, indicated by the substantial expansion of the lattice constant due to larger covalent Mn radius as observed by XRD and due to a high local tensile strain determined from mu RS. This interpretation is also supported by recent calculations, showing that it is energetically favorable for Mn to substitute Si sites. The temperature dependence of magnetization shows an insulatinglike character for the as-implanted film and metalliclike for the annealed-implanted film with Curie temperature above RT. In addition, the magnetic moment per Mn increases strongly with annealing from 0.23 to 0.65 mu(B). The experimental behavior is supported by our ab initio calculations, showing that magnetism in Mn-doped 3C-SiC can be enhanced by carefully growing a structure with Mn in Si sites using a C-deficient SiC host, possibly resulting in localized magnetic interactions.

Abstract: Evolution of magnetic excitations from purely magnetostatic modes to dipole-exchange spin waves in the Damon-Eshbach geometry in nanocomposite (SiO2)(100-x)Co-x (50 at. % <x<80 at %) films during a transition from superparamagnetic to superferromagnetic state has been studied by Brillouin light scattering. It has been shown that removal of the degeneracy of backward volume magnetostatic waves due to nonzero exchange constant manifests itself in more pronounced Stokes/ anti-Stokes asymmetry. Accompanying static characterization by means of magnetic force microscopy imaging and grazing incidence small angle neutron scattering has demonstrated the presence of weak stripe domains in the superferromagnetic phase. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3009339]

Abstract: A microwave assisted Brillouin light scattering (BLS) technique based on resonant excitation of spin waves in a 200 nm thick permalloy film by a micrometric size coplanar antenna has been studied. It has been demonstrated that the BLS intensity and signal-to-noise ratio have been improved by three orders of magnitude with respect to the conventional light scattering by thermal magnons. The analysis of the amplitude, shape, and frequency position of Stokes and anti-Stokes lines in the BLS spectra, for nonzero angles of the light incidence, indicates the presence of a strong hybridization of standing spin-wave resonances with propagating spin waves due to partial nonsymmetric pinning on the film surfaces. Direct optical probing has shown that the excited hybrid spin-wave modes are localized strictly in the vicinity of the microwave antenna. (c) 2007 American Institute of Physics.

Abstract: Structural and elastic properties as well as lattice dynamics of ternary MgSxSe1-x alloy have been studied using first-principles calculations. These are done using density functional theory (DFT) and density functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We found that the lattice parameters, the elastic constants and the phonon frequencies follow a quadratic law in x.

Abstract: Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C-11 = 362 GPa and (C-11 - C-12)/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C-11 + 2C(12))/3 = 200 GPa. The ratio epsilon(0)/epsilon(infinity) = 3.1 and the optic permittivity epsilon(infinity) = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c(11) = 340, c(12) = 127 and c(44) = 112 GPa, of the bulk modulus B = (c(11) + 2c(12))/3 = 198 GPa, of the zone-center (Gamma) phonons and of the permittivity function provide good comparison with our experimental results. (C) 2007 Elsevier Ltd. All rights reserved.

Abstract: We have shown a strong texture effect on elastic properties of gold thin films deposited by physical vapour deposition. Elastic properties of non-textured and 111 fiber textured gold thin films were investigated by x-ray diffraction combined with in-situ tensile testing and Brillouin light scattering. These static and dynamic methods allowed characterizing the local and macroscopic elastic behavior of gold films.

Abstract: High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (omega(TO) and omega(LO)), the high-frequency dielectric coefficient (epsilon(infinity)) and the dynamic effective charge (Z*) with pressure. The omega(TO) and omega(LO) have a quadratic form with pressure for all boron compounds. The obtained epsilon(infinity) and Z* for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, epsilon(infinity) and Z* have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.

Abstract: Brillouin light scattering has been used to investigate the elastic properties of high quality homoepitaxial diamond layers about 1 mm thick that have been elaborated by microwave plasma assisted chemical vapour deposition. Taking advantage of the detection of different acoustic modes, a complete elastic characterization of the crystal has been achieved. Three single crystal elastic constants, namely, c(11), (c(11)-c(12))/2 and c(44) have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes travelling parallel to the film surface. These determinations are in agreement with the frequency of the observed surface modes and of the bulk waves propagating at different angles from a normal single crystal film plane and consistent with the properties of natural diamond. By adding a low amount of nitrogen ranging from 2 to 50 ppm in the gas phase, the growth rates were increased from 6 to 33 mu m/h whereas the mechanical properties of the resulting layers remained close to those of natural diamond. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: We present a Brillouin light scattering study of a thick ferromagnetic single layer Ni80Fe20 (44 nm) film, using two different geometrical setup: (i) the so-called Damon-Eschbach (DE) geometry where the in-plane wave vector Q(11) of the studied spin wave is perpendicular to the external magnetic field H and (ii) the back-ward geometry (BW) where it is parallel to H (Q(11) and H lie in the film plane). An in-plane uniaxial anisotropy that do not exceed 100 Oe is evidenced through the analysis of the variations of DE mode frequency and of the Stokes/anti-Stokes dissymmetry versus H. The experimental magnetic Brillouin spectra showing the presence of dipolar and exchange standing spin waves are well reproduced for both geometries by our calculations of the scattered intensity using the following magnetic parameters: 4 pi M = 9400 G; g = 2.13; A = 0.93 10(-6) erg.cm(-1) for different values of the magnetic field H and of the in-plane wave vector amplitude Q(11). (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract: Thin films of CNx deposited by physical vapor deposition (PVD) with different contents of nitrogen have been studied. An RF-powered antenna was added to a classical magnetron sputtering system. The addition of an antenna plays an important role in mechanical and physicochemical properties. The films have been characterized using XPS, AFM, Brillouin light scattering, grazing angle FTIR, and wettability test. The results show in particular that the Rayleigh wave velocity determined by BLS increased when deposit is assisted by the antenna. Refractive index and surface tension are also enhanced with the use of an antenna. Moreover, high deposition rates are obtain with antenna without modification of N/C ratio. (c) 2004 Elsevier B.V. All rights reserved.

Abstract: The interdependence between the microstructure of sputter-deposited Ni(111)/Mo(110) superlattices and their elastic behavior is investigated as a function of the bilayer period (Lambda). Brillouin light scattering measurements show that a drastic softening of the effective shear modulus occurs with decreasing Lambda, until Lambda=2 nm where it reaches -62%. Ion irradiation is here used to trigger stress relaxation and to induce, in a controlled way, interdiffusion and structural changes allowing us thus to investigate their influence on the elastic anomaly. At a very low irradiation dose (0.1 displacements per atom), the relief of the lattice expansion and associated compressive stresses does not induce any change of the elastic response, which indicates that the elastic behavior of the as-grown multilayers is not correlated with the presence of elastic strains. Furthermore, a detailed x-ray diffraction analysis shows that the unstrained lattice parameter of Mo layers exhibit a linear dependence with the interface density, while the Ni unstrained lattice parameter remains nearly unchanged in the same Lambda range. This effect can be attributed to an interfacial mixing of a constant Ni amount (similar to1.5 monolayers) into the Mo layers, as a consequence of a dynamic segregation of Ni atoms during growth. Thus, the formation of interfacial metastable and supersaturated solid solutions, structurally and mechanically unstable, appears as the origin of the huge elastic softening observed in this system. At high ion fluences, when the mixing process becomes dominant, the present study also provides experimental data on phase transformation in �driven� alloys, by addressing the issue of the stability of out-of-equilibrium structures under irradiation.

Abstract: Brillouin light scattering has been used to investigate the elastic properties of polycrystalline smooth fine-grained diamond films having various diamond quality. They have been deposited on titanium alloy Ti-6Al-4V by a two-step microwave plasma-assisted chemical vapour deposition process at 600degreesC. Taking advantage from the detection of a number of different acoustic modes, a complete elastic characterization of the films has been achieved.

Abstract: Direct elastic properties measurements of beta-SiC films have been made using the interferometric strain gage displacement (ISDG) technique and compared with data acquired by the Brillouin light scattering (BLS) technique. BLS permits to selectively determine the three independent elastic constants (c(11) = 395 GPa; (c(11) - c(12))/2 = 136 GPa and c(44) = 236 GPa) of a beta-SiC single crystal epitaxial film from the analysis of a number of different surface acoustic modes. The calculated Voigt average values of the elastic constants for the <111> textured polycrystalline films (C-11 = 500 GPa, C-33 = 534 GPa, C-44 = 166 GPa, C-66 = 201 GPa, C-13 = 62 GPa) using the single crystal constants provides good agreement with experimental results on Young�s modulus measured by the ISDG technique. Nevertheless, BLS gave more accurate values of Poisson�s ratios. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Synthetic diamond thin or thick films are suitable materials for many applications because of their weak friction coefficient and their large hardness, Young modulus, and thermal conductivity. A series of diamond thin films of variable quality obtained by plasma-assisted chemical vapor deposition lying on titanium alloy substrates has been studied by picosecond ultrasonics. Femtosecond laser pulses allow the generation and detection of picosecond acoustic pulses that can be used to study the elastic properties of thin micrometric and submicrometric films. Acoustic fields generated in the substrate and propagating in the transparent diamond film are detected by an interferometric technique; they give rise to oscillations and abrupt step-like changes in the transient reflectivity variations. An analysis of these different features allows the determination of various characteristics of these films, such as longitudinal elastic constant, thickness, and roughness in terms of the diamond quality. (C) 2004 American Institute of Physics.

Abstract: Brillouin light scattering has been used to investigate elastic properties of a monocrystalline and of <111> textured polycrystalline 3C polytype silicon carbide films that have been deposited on silicon substrate by chemical vapor deposition. Taking advantage from the detection of different acoustic modes, a complete elastic characterization of the films has been achieved. The three unknown elastic constants of the monocrystalline 3C-SiC, namely, c(11)=395 GPa, (c(11)-c(12))/2=136 GPa, and c(44)=236 GPa have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes traveling parallelly to the film surface. These determinations are in agreement with the frequency of the observed Rayleigh surface mode, of the pseudosurface mode, and of the bulk waves propagating at different angles from the normal of the single crystal film plane and consistent with existing theoretical calculations of beta-SiC elastic constants. Finally, the calculated Voigt average values of the effective elastic constants for the (111) textured 3C-SiC polycrystalline film using the single crystal constants provides a good agreement with our experimental results (C-11=500 GPa, C-33=535 GPa, C-44=165 GPa, C-66=210 GPa, and C-13=50 GPa) and compare fairly well with the alpha-SiC published one. These results confirm that the elastic constants of silicon carbide are slightly influenced by the polytypism. (C) 2004 American Institute of Physics.

Abstract: Picosecond ultrasonics and Brillouin light scattering were used to investigate the acoustical properties of periodic (Py-Al2O3) multilayers constituted of ultrathin polycrystalline layers of permalloy (Py corresponding to a Ni80Fe20 alloy) separated by a dielectric spacer of amorphous alumina (Al2O3). Picosecond ultrasonics gives access to the elastic properties of multilayers both through the travel time of acoustic echoes propagating in the whole structure and through the frequencies of localized vibrational modes lying within the gaps induced by the periodicity of the system. These measurements show that the effective longitudinal elastic constant along the bilayer stacking axis, softens from 7% to 40%, with respect to a reference value obtained in thick samples, when the period decreases from 14.8 to 5.3 nm. This strong softening is ascribed to interfacial effects between permalloy and alumina layers. In contrast with the longitudinal elastic constant, the softening of the in-plane shear elastic constant, derived from Brillouin light scattering measurements, does not exceed 10% for the smallest period sample.

Abstract: The Brillouin light scattering was used to investigate elastic properties of the zinc blende, MBE-grown MnTe layer that was deposited on a (001) GaAs substrate covered by CdTe buffer layer. The three elastic constants of the zinc blende MnTe, namely c(11), c(12), and c(44), were directly determined for the first time from the frequency of the Rayleigh mode, of the pseudo-surface mode, and of the shear horizontal bulk mode traveling parallel to the layer surface. The value of C-11 was checked using the frequency of longitudinal bulk waves propagating at different angles from the normal of the layer plane. This value was also independently determined by results of the folding of acoustic phonons, observed for MnTe/CdTe superlattices by the Raman scattering. Finally, the bulk modulus given by the formula B = (c(11) + 2c(12))/3 was determined for zinc blende MnTe by ab initio calculations making use of the density functional theory and atomic pseudopotentials; spin polarization of MnTe was taken into account. A satisfactory agreement between theoretical and experimental values was obtained.

Abstract: AlN thin films have been deposited on Si(100) substrates by a pulsed laser deposition method. The deposition parameters (pressure, temperature, purity of target) play an important role in the mechanical and physicochemical properties. The films have been characterized using Xray diffraction, atomic force microscopy, Brillouin light scattering, Fourier transform infrared spectroscopy and wettability testing. With a high purity target of AlN and a temperature deposition of 750 degreesC, the measured Rayleigh wave velocity is close to the one previously determined for AlN films grown at high temperature by metal-organic chemical vapour deposition. Growth of nanocrystalline AlN at low temperature and of AlN film with good crystallinity for samples deposited at higher temperature is confirmed by infrared spectroscopy, as it was by atomic force microscopy, in agreement with X-ray diffraction results. A high hydrophobicity has been measured with zero polar contribution for the surface energy. These results confirm that films made by pulsed laser deposition of pure AlN at relatively low temperature have good prospects for microelectromechanical systems applications. (C) 2004 Elsevier Ltd. All rights reserved.

Abstract: 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-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. (C) 2003 American Institute of Physics.

Abstract: Carbon nitride thin films deposited by reactive RF magnetron sputtering were studied to obtain knowledge for various applications. Different types of analyses were performed on CNx layers to determine both surface and bulk properties of the films and particular attention was paid to nitrogen incorporation in the films. The variation in composition and type of chemical bonds between atoms in the films was followed using X-ray photoelectron spectroscopy (XPS). The results showed that the N/C ratio reaches 0.7. The wettability tests can lead to the determination of superficial energy. providing very interesting information about biocompatibility. The wettability and superficial energy decreased with nitrogen content. The evolution of the elastic properties of the CNx layers as a function of the nitrogen incorporation was investigated by Brillouin spectroscopy. The measured Rayleigh wave velocity decreased with nitrogen incorporation. (C) 20021 Elsevier Science B.V.. All rights reserved.

Abstract: Mechanical and surface properties associated with their wettability were investigated for diamond films deposited on titanium alloy by a two-step microwave PACVD process at 600 degreesC. Polycrystalline and smooth fine grained diamond films were investigated. The elastic properties of the diamond layers were studied by Brillouin light scattering spectroscopy in order to determine their evolution as a function of the diamond purity. The effective elastic properties of these films with hexagonal effective symmetry were determined. The elastic constants decrease when diamond purity is lowered. The wettability tests can lead to the determination of superficial energy. A strong correlation is noticed between the wettability and superficial energy with the content Of Sp(2). (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: The importance of the interfaces in governing the elastic behavior of nanometer-scale metallic superlattices has long been recognized, although their intrinsic nature and the underlying physical mechanisms are still subject to controversy. In the present study, the key role of an interfacial alloying effect on the dramatic softening (-62%) in the shear elastic constant C-44 of Ni/Mo multilayers is clearly evidenced. By combining x-ray diffraction and Brillouin light scattering experiments on both Ni/Mo superlattices and Ni1-xMox solid solution samples, we show that the formation of metastable alloys, obtained either by cosputtering or stabilized at the interfaces, induces an elastic lattice instability. In addition, the extremely low value of C-44 observed for the multilayers, at small modulation periods, suggests the stabilization under epitaxial growth of a highly supersaturated interfacial alloyed layer.

Abstract: The Knoop hardness of the highly incompressible cubic phase of ruthenium dioxide was found to be 19-20 GPa from indentation tests. This value scales well with the shear modulus approximated by the elastic constant C-44 of 144 GPa obtained from Brillouin scattering measurements. This work provides evidence that the shear modulus is a better indicator of hardness than the bulk modulus for ionic and covalent materials. (C) 2001 American Institute of Physics.

Abstract: Some general features concerning inelastic light scattering by hypersonic waves are exposed and it is shown that Brillouin spectroscopy can be fruitfully applied in order to study the elastic proper-ties of thin and ultrathin films as well as of multilayers and superlattices. A brief presentation of the various kinds of surface waves and of the mechanisms which monitor the scattering by these excitations is provided. Examples concerning transparent and opaque structures are given. The important influence of the interfaces is pointed out.

Abstract: The photoelastic response of periodic arrays of stripes attached to the surface of a substrate and illuminated by an ultrashort laser pulse were investigated. The samples were gold arrays on silicon and aluminum arrays either on crystalline quartz or on silicon. The metallic stripes had submicrometer lateral dimensions and the spatial periods ranged from about 1 mum up to 5 mum. The substrate being transparent (quartz) or slightly absorbing (silicon) at the laser wavelength (lambda =750 nm), a laterally modulated thermal stress is generated near the surface of the substrate when a light pulse illuminates the structure. The studies of vibrations involved by the subsequent relaxation processes show that surface acoustic waves at frequency as high as about 5 GHz are excited with the samples consisting of aluminum stripes. In the case of the aluminum samples with the largest lateral spatial periods (aluminum on quartz), the surface acoustic wave propagates outside the illuminated area. In the case of the gold samples, a normal mode of individual bars is observed instead. Experimental evidence shows that these behaviors are mainly governed both by the lateral spatial period of the structure and by the density of the metal. (C) 2001 Acoustical Society of America.

Abstract: Brillouin light scattering, Raman light scattering and x-ray diffraction were used to investigate the elastic and microstructural properties of polycrystalline and smooth fine-grained diamond films of varying diamond quality. They were deposited on a titanium alloy by a two-step microwave plasma-assisted chemical vapor deposition process at 600 degreesC. Their morphology and roughness were studied by scanning electron microscopy and atomic force microscopy. Their refractive indices were determined by the Wine spectroscopy technique. The diamond purity of all these coatings in terms of the sp(3) bonding fraction was deduced from visible and UV Raman spectroscopy as a function of the deposition conditions. All the samples were found to be textured with a (011) crystallographic direction normal to the film plane, leading to essentially hexagonal symmetry of the elastic tensor. By taking advantage of the detection of a number of different acoustic modes, complete elastic characterization of the films was achieved. The elastic constants C-11 and C-66, respectively, were selectively determined from the frequency of the longitudinal and shear horizontal bulk modes traveling parallel to the film surface. The three remaining elastic constants, namely, C-44, C-33 and C-13, were obtained from detection of the Rayleigh surface wave a bulk shear wave and the bulk longitudinal wave propagating at different angles from the normal to the surface. The values of the elastic constants depend on the deposition conditions and on the microstructural properties of the films, especially the diamond quality and the polycrystalline or smooth fine-grained nature of the diamond. For the polycrystalline diamond film with the best quality, the elastic constants are rather close to the Voigt or Reuss average estimate values using known bulk elastic constants of diamond, whereas those of the smooth fine-grained diamond films are reduced because of the poorer diamond quality leading to lower residual stress in the films. (C) 2001 American Institute of Physics.

Abstract: Brillouin scattering has been used to investigate the elastic properties of CuxMo1-x thin films with thicknesses varying from 200 up to 430 nm, elaborated by ion beam sputtering. Two compositions around Cu30Mo70 and Cu70Mo30 and pure Cu and Mo films have been studied. The samples are essentially randomly oriented polycrystals, leading to an isotropic effective symmetry. By fitting all the Brillouin spectral lines, two independent effective elastic constants of these films have been determined, allowing the calculation of their elastic moduli. Results indicate that pure copper thin films� elastic properties are similar to the bulk copper ones whereas pure molybdenum thin films� Young�s modulus is weaker (about 10%) than the bulk Mo one. Concerning Cu-Mo solid solutions, elastic constants values lie between pure copper and molybdenum ones. Finally, the effect of annealing at 760 K on the mechanical properties of the solid solutions in relation with the microstructural evolution is discussed. The annealed solid solutions show a hardening of the elastic moduli with respect to the as-deposited samples, which is supposed to reflect their full demixing. (C) 2001 American Institute of Physics.

Abstract: Mo/Ni multilayers are investigated by x-ray diffraction and Brillouin light scattering before and after ion induced stress relaxation and mixing. Study of the evolution of interplanar distances in both layers as a function of the period exhibits a strong anomaly of the Mo (110) distance (in the growth direction) that can be correlated with the elastic anomaly. The very low interplanar distance in the molybdenum layers found after stress relaxation seems to favor an explanation of this behavior based on the diffusion of Ni in the Mo layers during the growth.

Abstract: We report on acoustic surface waves in quasicrystal Al70.4Mn8.4Pd21.2 studied using Brillouin spectroscopy. Our data are fitted with a spectral density modelization and our results are compared to those obtained from previous inelastic neutron scattering and ultrasonic propagation measurements on the bulk samples Al68.7Mn9.6Pd21.7. (C) 1998 Elsevier Science Ltd. All rights reserved.

Abstract: We present a Brillouin scattering study of single and multilayers thin (1,1,1) textured films of Permalloy with amorphous alumina interfaces prepared by rf sputtering [1]. From the spin wave spectra we can determine the gyromagnetic factor and the total anisotropy field. The results are in agreement with FMR experiments performed on the same samples [1]. We confirm the existence of a rather large surface anisotropy (K-s = 0.35 erg cm(-2)). The surface elastic wave spectra are also analysed: the deduced effective shear stiffness constant C-44 of Permalloy agrees with theoretical predictions.

Abstract: Magnetic domain studies, Brillouin scattering experiments and microwave spectroscopy were performed on Co/Cr/Co trilayers. For d(Cr) < 10 Angstrom, strong ferromagnetic coupling is found, while above 10 Angstrom of Cr the interlayer coupling is negligible. In ultra high vacuum deposited samples with d(Cr) about 15 Angstrom, an antiferromagnetic coupling was found (K-c approximate to -0.1 erg/cm(2)), accompanied by a transition to a patch domain pattern.

Abstract: Some general features concerning inelastic light scattering by thermal excitations : acoustic waves or spin waves, are exposed. Trough many illustrations, it is shown that Brillouin spectroscopy can be fruitfully applied in order to study the elastic properties or the magnetic properties of thin films as well as of multilayers. A brief presentation of the various kinds of surface waves or bulk waves and of the mechanisms which monitor the scattering by these excitations is provided. Examples concerning transparent and opaque structures are given. A particular attention is paid to the influence of the interfaces on some results.

Abstract: