Philippe Djemia

Elastic properties of β-SiC films by Brillouin light scattering

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, c11=395 GPa, (c11−c12)/2=136 GPa, and c44=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 β-SiC elastic constants. Finally, the calculated Voigt average valu...

First-principles calculation of the structural and elastic properties of ternary metal nitrides TaxMo1-xN and TaxW1-xN

First-principles pseudo-potentials calculations of the mixing enthalpy, of the lattice constants a0 and of the single-crystal elastic constants cij for ternary metal nitrides TaxMe1-xN (Me=Mo or W) alloys considering the cubic B1-rocksalt structure is carried out. For disordered ternary alloys, we employ the virtual crystal approximation VCA in which the alloy pseudopotentials are constructed within a first-principles VCA scheme. The supercell method SC is also used for ordered structures in order to evaluate clustering effects. We find that the mixing enthalpy still remains negative for TaxMe1-xN alloys in the whole composition range which implies these cubic TaxMo1-xN and TaxW1-xN ordered solid solutions are stable. We investigate the effect of Mo and W alloying on the trend of the mechanical properties of TaN. The effective shear elastic constant c44, the Cauchy pressure (c12-c44), and the shear to bulk modulus G/B ratio are used to discuss, respectively, the mechanical stability of the ternary structure and the brittle/ductile behavior in reference to TaN, MeN alloys. We determine the onset transition from the unstable structure to the stable one B1-rocksalt from the elastic stability criteria when alloying MeN with Ta. In a second stage, in the frame of anisotropic elasticity, we estimate by one homogenization method the averaged constants of the polycrystalline TaxMe1-xN alloys considering the special case of an isotropic medium with no crystallographic texture.

Brillouin scattering in ultrathin permalloy films: monolayers and multilayers with alumina interfaces

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.

Mechanical properties of elementary layers involved in a multilayer optical stack by photon-acoustic phonon interaction approaches

Two complementary techniques, picosecond ultrasonics (PU) and Brillouin light scattering (BLS), have been performed to measure the mechanical properties of layers involved in an optical stack. One of the advantages of these two techniques is their ability to analyze samples whose thickness varies from a few tens of nanometers (the anti-reflective coating) to several millimeters (the polymer substrate). Since all the layers constituting the optical stack have proved to be isotropic, they are completely elastically characterized thanks to the two techniques. Moreover, as the two independent elastic coefficients are measured by PU and BLS, c33 and c44, respectively, the complete stiffness matrix and, hence, the Poissons ratio and the Youngs modulus can be deduced.

Thin films of binary amorphous Zn-Zr alloys developed by magnetron co-sputtering for the production of degradable coronary stents: A preliminary study

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Study of the mechanical properties of thin films involved in ophthalmic glasses

The mechanical properties of thin films involved in the manufacturing of ophthalmic glasses have been investigated by two complementary laser based techniques. On the one hand, picosecond ultrasonics (PU) measurements allows to determine the acoustical longitudinal velocity in the sample, hence the elastic constant c11. On the other hand, Brillouin light scattering (BLS) measurements leads to the value of the transverse velocity, hence c44. In the case of isotropic materials, these two coefficients give a direct access to the value of the Young’s modulus and Poisson’s ratio of the film. The influence of the film characteristics on its mechanical properties will be discussed, mainly regarding its thickness and the manufacturing process. Another issue concerning the effect of the film environment will be addressed. Especially, we will discuss the influence of the substrate on the mechanical properties of a single film, and the link between the mechanical properties of a single film and the ones of a films s...