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The Brillouin spectroscopic measurements of elastic properties of polypropylene films fabricated by different processing techniques are described. We find that the elastic symmetry and the associated elastic constants are dependent on the molecular orientation brought about by the processing conditions used to produce the films. We have shown that Brillouin scattering techniques can successfully be used to track the molecular orientation induced by uniaxial stretching. We find a direct correspondence between the Brillouin measurements and optical birefringence measurements, illustrating that molecular orientation plays a dominant role in determining the mechanical anisotropy in these materials.

Brillouin scattering from single crystals of NiO show that, apart from the expected phonon peaks, there is a broad central peak. The phonon peaks have Fano-like lineshapes, indicating a strong coupling between them and the broad feature, and lead to elastic constants that differ considerably from ultrasonic values. The broad feature is probably ‘magnetic’ in origin since it disappears at the Neel temperature. We speculate that it may be the lower of the two AFMR modes predicted for easy-plane antiferromagnets but which has previously been observed only in EuTe and MnO. The interaction between the phonons and the ‘magnetic’ excitation provides a phenomenological explanation for the differences in the elastic constants determined by different techniques.

Brillouin scattering measurements have been carried out on single‐crystal lattice‐matched TiN/(V0.6Nb0.4)N and mismatched TiN/NbN superlattices. Measured surface wave velocities were found to be independent of superlattice wavelength over the entire range investigated, 1.5–30 nm, and were averages of the measured velocities of pure homogeneous TiN, NbN, and (V0.6Nb0.4)N. These results indicate that there is no anomaly in the C44 elastic constant. X‐ray diffraction results from the superlattices indicated that the average lattice spacing did not vary with wavelength. This is consistent with previous observations where elastic anomalies were related to changes in lattice spacing. The absence of a correlation between the C44 elastic constant and previously reported hardness enhancements indicates that the latter are not caused by anomalies in C44; they could, however, be correlated with other elastic moduli.

The shear elastic modulus and structural properties of a series of Ag Co superlattice films have been characterized using Brillouin scattering and X-ray diffraction. A softening of the shear modulus of the unirradiated Ag Co superlattices with decreasing modulation wavelength is observed and is correlated with an expansion in the average lattice spacing. With increasing irradiation fluence, a reduction in the anomalous shear modulus softening and lattice expansion are observed. These reductions imply that the anomalous elastic properties are related to lattice strains present, which are relieved by the irradiation.

The modulation wavelength dependence of the surface‐wave velocity in Cu/Ni superlattices has been investigated using Brillouin scattering. It is the first compositionally modulated system to be studied by this technique and the first for which elastic properties have been determined by both ‘‘macroscopic’’ methods and Brillouin scattering. Contrary to the enhancements previously reported in the biaxial modulus and in the Young’s modulus, the modulus associated with the surface‐wave velocity shows no evidence of anomalous behavior.

We have used Brillouin scattering to measure the temperature dependence of the sound velocities of the longitudinal and transverse vibrational modes in various directions in small single crystals of monoclinic ZrO2. Using these velocities and the Christoffel equation, we have calculated the 13 elastic stiffness moduli between room temperature and the monoclinic—tetragonal transformation temperature.

We report photoinduced antiferromagnetic (AF) interlayer coupling in sputtered Fe/(Fe-Si) superlattices. The superlattices are intrinsically AF coupled at room temperature and become increasingly ferromagnetically coupled when cooled below 100 K, but the AF coupling is restored at low temperature by exposure to visible light of sufficient intensity ([gt]10 mW/mm[sup 2]). These effects are due to charge carriers in the Fe-Si spacer layer which, when thermally or optically generated, are capable of communicating spin information between the Fe layers.

The elastic and structural properties of Cu/Pd and Cu/Ni superlattices have been determined. Microstructurally the films have the same growth mechanisms, growth textures, and composition modulation amplitudes, as in past studies where the ``supermodulus effect'' was reported. Advanced techniques have been used to measure the flexural, shear, and Young's moduli of the thin films, and no significant anomalous elastic behavior has been observed.

Using Brillouin scattering we have succeeded in observing the normal modes of vibration of unsupported films in a region where the dispersion relationship is quadratic. Extremely low-lying excitations were observed in thin films with thicknesses as small as 200 A\r{}. Contrary to what has been found in work on supported films, we are able to extract information on a number of the elastic moduli because the measured velocities in very thin films do not depend on the properties of the substrate. This technique should be a valuable addition to the tools which can be used in the study of materials in thin-film form.

Brillouin-scattering measurements show an anomalous dip in the elastic constants of Nb/Cu superlattices for superlattice wavelengths of \ensuremath{\lesssim} 100 \AA{}. This dip is correlated with changes in the electrical resistivity of the samples giving the first evidence that electronic effects are responsible for phonon softening in these materials.

The crystalline-to-amorphous (c-a) phase transformation in the intermetallic compound Zr 3 Al during room temperature bombardment with 1.0 MeV Kr + was investigated. Transmission electron microscopy and Brillouin scattering techniques were used to determine the lattice parameter and shear elastic constant as a function of the degree of long-range order. The results show that a large (about 50%) elastic softening and dilatation strain (about 3%) due to disordering precede the onset of amorphization. These results indicate that chemical disordering is an important driving force for the c-a transformation and that the mechanism is an elastic shear instability. It is also shown that the volume dependence of the shear elastic constant associated with radiation-induced disordering and eventual amorphization is virtually identical to that associated with the heating to melting of many solids. The origin and implications of this parallelism between solid state amorphization and melting are discussed.

Metallic superlattices of nickel and molybdenum have been synthesized for a wide range of layer thicknesses by alternate sputtering. X-ray examination shows that they are composed of layers of fcc nickel and bcc molybdenum oriented along [111] and [110] directions, respectively. Anomalies have been observed in the lattice spacings, elastic moduli, and electrical resistivity versus modulation wavelength. These anomalies occur simultaneously at the same superlattice wavelength. The anomalies have been interpreted as due to strains in the nickel lattice.

We have performed a study of magnons in Mo/Ni metallic superlattices with the use of Brillouin scattering. The magnetic field and modulation wavelength dependence of the magnon frequencies are found to be in reasonable agreement with theoretical predictions. Certain features in the spectra which are characteristic of a superlattice and cannot be expalined by a trivial superposition of the spectra of the individual constituent layers are presented and discussed.

The biaxial moduli of free‐standing metallic films have been determined from their behavior as elastically tensioned membranes. Errors due to thickness determination and warping of the films are eliminated, thereby opening up the possibility of solving a number of controversial issues. The method combines the determination of stress from the frequency of the membrane modes with optical measurements of strain. Tests on Ta and Ni films yield values of the biaxial modulus in good agreement with calculated literature data.

International audience; The properties of solid krypton have been measured as a function of pressure in a diamond-anvil cell using energy-dispersive x-ray diffraction and Brillouin scattering. A room-temperature equation of state and a complete set of elastic constants are deduced. The analysis of these results indicates a possible phase transition above 30 GPa.

Brillouin scattering in GaS crystals had been measured under hydrostatic pressures up to 17.5 GPa. Frequency shifts of the Brillouin lines give the pressure dependence of the elastic constants C11 and C33, and the index birefringence. Exponents derived from Murnaghan’s equation of state are compared with a Lennard‐Jones description of interatomic forces in GaS.

Anharmonic effects in crystals typically result in the symmetric broadening of the single-phonon Lorentzian line shape. However, a simple model, based on consideration of a highly anharmonic potential, shows that anharmonicity can lead not only to asymmetric line shapes but also to line shapes composed of multiple subpeaks. Experimental Raman data on the soft ${\mathit{A}}_{1}$(TO) phonon in ferroelectric ${\mathrm{PbTiO}}_{3}$ indicates that this mode does indeed consist of a series of subpeaks whose intensities are accurately predicted (with no fitting parameters) by our model.