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 °C. Their morphology and roughness were studied by scanning electron microscopy and atomic force microscopy. Their refractive indices were determined by the M-line spectroscopy technique. The diamond purity of all these coatings in terms of the ${\mathrm{sp}}^3$ 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.

Picosecond ultrasonics and Brillouin light scattering were used to investigate the acoustical properties of periodic $\left(\mathrm{Py}\text{−}{\mathrm{Al}}_2{\mathrm{O}}_3\right)$ multilayers constituted of ultrathin polycrystalline layers of permalloy (Py corresponding to a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ alloy) separated by a dielectric spacer of amorphous alumina $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$. 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 $14.8\text{to}5.3\mathrm{nm}$. 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.

Effects of Alkali Treatment on the Microstructure, Composition, and Properties of the Raffia textilis Fiber