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We report a detailed analysis of the dynamic structure factor of glassy sorbitol by using inelastic X-ray scattering and previously measured light scattering data [B. Ruta, G. Monaco, F. Scarponi, and D. Fioretto, Philos. Mag. 88, 3939 (2008)]. The thus obtained knowledge on the density-density fluctuations at both the mesoscopic and macroscopic length scale has been used to address two debated topics concerning the vibrational properties of glasses. The relation between the acoustic modes and the universal boson peak (BP) appearing in the vibrational density of states of glasses has been investigated, also in relation with some recent theoretical models. Moreover, the connection between the elastic properties of glasses and the slowing down of the structural relaxation process in supercooled liquids has been scrutinized. For what concerns the first issue, it is here shown that the wave vector dependence of the acoustic excitations can be used, in sorbitol, to quantitatively reproduce the shape of the boson peak, supporting the relation between BP and acoustic modes. For what concerns the second issue, a proper study of elasticity over a wide spatial range is shown to be fundamental in order to investigate the relation between elastic properties and the slowing down of the dynamics in the corresponding supercooled liquid phase. [ABSTRACT FROM AUTHOR]

Brillouin light scattering has been used to investigate the density fluctuations of the fragile glass-former sorbitol in the GHz frequency range and at temperatures between 20 and 294 K. Longitudinal acoustic sound velocity and attenuation data are here reported and discussed. These data are used to test the existence of a correlation between elastic properties of glasses and viscous properties of the corresponding deeply undercooled melts above the glass transition temperature, Tg. In particular, and as for other fragile systems, the ratio of the vibrational to the relaxational compressibility at Tg is found to be basically independent of fragility. [ABSTRACT FROM AUTHOR]

The dynamics of density fluctuations of aqueous glucose solutions were studied in the water-rich region by means of Brillouin ultra-violet scattering. The temperature dependence of the position and line-width of inelastic peaks gives evidence of a strong relaxation process located in the picosecond timescale. In the approximation of a single exponential process, the relaxation time, τ, was obtained for different glucose concentrations; its temperature dependence is well described by an Arrhenius law characterized by an activation energy comparable to that of pure water. This result supports the hypothesis that the microscopic mechanism responsible for the main relaxation process in sugar-water solutions is the continuum rearrangement of the hydrogen-bond network. A comparison is also reported with previous results on aqueous trehalose solutions, showing the acoustic absorption scales with the number of glucoside units for both glucose and trehalose aqueous solutions. [ABSTRACT FROM AUTHOR]

The dynamics of liquid sulphur have been investigated in the temperature region corresponding to the so-called λ transition by means of Brillouin light scattering. Results of this work, together with ultrasonic spectroscopy and inelastic X-ray scattering results in literature, indicate that the main structural relaxation is slightly affected by the transition and suggest that the dramatic increase of shear viscosity is related to the onset of a low-frequency additional relaxation. Such a feature is commonly found in rubber-like materials and can be related to the polymerization of sulphur molecules across the transition. [ABSTRACT FROM AUTHOR]

Brillouin light and X-ray scattering have been used to investigate the dynamic structure factor of supercooled and glassy m-toluidine in the temperature range 34-303 K. In addition to the ubiquitous α-relaxation, evidence is given of a fast relaxation process active in the ns-ps time region. Data on activation energy of the fast process are obtained from the attenuation of longitudinal acoustic modes. [ABSTRACT FROM AUTHOR]

An array of multilayered rectangular NiFe/Cu/NiFe dots (lateral dimensions 720 × 430 nm, thicknesses 10/10/10 nm) has been fabricated by electron-beam lithography. The magnetization reversal process has been studied by the magneto-optical Kerr effect, showing that the dipolar coupling between the two magnetic layers plays an important role and competes with shape anisotropy, determining the characteristic profile of the hysteresis curve. Moreover, both conventional and microfocused Brillouin light scattering have been exploited to study the eigenmodes spectrum in the gigahertz range, achieving a direct visualization of the spatial profile of the different modes. The results are in good agreement with both the modes frequency and the spatial profiles obtained by micromagnetic simulations. [ABSTRACT FROM AUTHOR]

Abstract: We present here a study of the acoustic dynamics of polymeric glassy sulfur. The data have been collected in the GHz frequency range by means of Brillouin light scattering for different scattering geometries. The choice of the experimental setup allows us to obtain information on the refractive index, n, that comes out to be close to that corresponding to the high temperature polymeric liquid phase. The longitudinal acoustic excitations have been investigated as a function of temperature from deep into the glassy state up to the glass transition temperature. The temperature dependence of the sound velocity is compared to the one measured in the liquid phase. We find that the sound velocity of the glass can be linearly extrapolated from that of the polymeric liquid measured in the THz frequency range with inelastic X-ray scattering. [ABSTRACT FROM AUTHOR]

Abstract: We report depolarized light scattering measurements of water–glucose solutions in a wide spectral range from 0.01 to 1000cm−1, performed by the combined use of a double monocromator and a multipass Fabry–Perot interferometer. For the first time evidence is given of a low frequency relaxation process related to the glucose dynamics well separated from that of water. This low frequency process has a different origin with respect to the broad relaxation feature detected by dielectric spectroscopy and is interpreted in terms of Stokes–Einstein–Debye rotational diffusion of single glucose molecules. [Copyright &y& Elsevier]

Abstract: Brillouin spectra of glycerol measured in the visible, ultraviolet and X-ray frequency regions allow us to reckon the imaginary part of acoustic compliance, J″(ω), over a broad frequency range from fraction of GHz to tens of THz. We observe that J″(ω) suitably mimic the shape of the tagged particle susceptibility, χ″ INS (ω), measured by incoherent neutron spectra for both the liquid and supercooled states. The proportionality between these two quantities suggests a strict relationship between acoustic dissipation and generalized density of states. [ABSTRACT FROM AUTHOR]