Search

Brillouin light scattering was applied for the investigation of surface waves propagation in phononic materials made of a silicon substrate loaded with a permalloy layer and a modulated nanostructure of aluminum stripes. The results revealed the impact of one-dimensional modulation of the surface phononic crystal on the propagation of surface acoustic waves along the modulated aluminum stripes. The dispersion relation was experimentally and theoretically investigated. The new modes propagating in the investigated structure are localized in the stripes and are defined. [ABSTRACT FROM AUTHOR]

Brillouin light scattering was used to study surface acoustic wave propagation in platinum (111) and ruthenium (0001) single crystals, both clean and loaded with a few-nanometre-thick epitaxial magnetite (111) film. The results revealed the influence of the film loading on the velocity of surface acoustic wave propagation in the studied samples. The surface acoustic modes were additionally analysed by finite element method simulations. [ABSTRACT FROM AUTHOR]

The paper presents the influence of the martensitic phase transition on hypersonic thermally excited surface acoustic waves propagating in Cu–14%Al–4%Ni (wt%) shape memory alloy. Non-destructive and non-contact testing using Brillouin light scattering spectroscopy permitted determination of the elastic constants of austenite versus temperature. Experimental results obtained for martensite were interpreted using the proposed model of the cubic to orthorhombic martensitic phase transition based on the Landau model of a first-order phase transition. Additionally we adopted the approximation of the domain structure of martensite by a polycrystalline sample using the Voigt–Reuss–Hill procedure of averaging the elastic constants. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical properties of ternary Y–Cu–Al alloys produced by the melt spinning method have been investigated by Brillouin spectroscopy and combined with calculations of the effective moduli method. Structural studies and TEM images demonstrated that the alloy can form amorphous, two- and three-phase composite and polycrystalline microstructures. The elastic moduli of ribbons with different microstructures were estimated as a function of the volume fraction of the YCu nanocrystallites. It is shown that the ductility of the amorphous and two-phase composite forms are comparable to that of the YCu single crystal. The formation of YCuAl crystallites, in addition to the YCu crystallites, lowers the ductility of the alloy. [Copyright &y& Elsevier]

Lattice disturbances caused by a soft bulk mode can be treated as displacement of entire lattice planes. The displacement is also visible on the surface of the crystal and can be detected from the behaviour of the surface phonons. In the crystals of lithium-caesium sulphate some anomalies in the behaviour of certain surface phonons have been detected by the surface Brillouin scattering. A model of the interactions of the soft bulk modes with the surface modes has been proposed to predict which surface phonons can reveal anomalies in the phase transition region. [ABSTRACT FROM AUTHOR]

High-resolution Brillouin spectroscopy was used to study elastic properties of two n-alkane/urea inclusion compounds CO(NH 2 ) 2 /C 20 H 42 and CO(NH 2 ) 2 /C 22 H 46 . Elastic anomalies were detected for the phonons propagating in the XY plane at T C = 195 K and 175 K, in these two compounds respectively. Some additional vibrations related to the guest sublattice were observed. [ABSTRACT FROM AUTHOR]

The existence of the ferroelastic phase transition at Tc = 191 K in n-icosane/urea single crystal has been confirmed. Brillouin scattering spectroscopy has been performed, and the room temperature elastic constant have been determined. The excitations which probably correspond to an existence of a sliding mode (phason) and/or reorientational motions of the n-icosane guest chains have been detected. [ABSTRACT FROM AUTHOR]

Results of the Brillouin scattering on the surface phonons propagating in ferroelastic crystal LiCsSO4 (LCS) in the temperature range covering its phase transition are presented. Surface acoustic phonons in different planes and at various depths from the surface have been studied. [ABSTRACT FROM AUTHOR]

Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed. [ABSTRACT FROM AUTHOR]

We present experimental and theoretical evidence of a phononic band gap in a hypersonic range for thermally activated surface acoustic waves in two-dimensional (2D) phononic crystals. Surface Brillouin light scattering experiments were performed on the (001) surface of silicon, loaded with a 2D square lattice of 100- or 150-nm-high aluminum pillars with a spacing of 500nm. The surface Brillouin light scattering spectra revealed a different type of surface mode, related to the modulation of the lattice structure and the mechanical eigenmodes of the pillars. The experimental data were in excellent agreement with theoretical calculations performed using the finite-element method. [ABSTRACT FROM AUTHOR]