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Brillouin scattering spectra of water from T=30 °C down to supercooling temperatures of about T=−26 °C have been measured, at different scattering angles and for different exciting wavelengths, covering exchanged wave vector values from 0.0137 to 0.0351 nm−1. A fit of the spectra using the hydrodynamic line shape for a simple fluid confirms the existence of a relevant dispersion in the wave vector dependence of the hypersonic sound velocity. The parameters obtained fitting the data with a relaxing hydrodynamic model indicate the ratio between volume and shear viscosity is almost temperature independent also in the supercooled regime and that a single relaxation process, involving almost entirely both shear and volume viscosities, accounts for the observed dispersion. The infinite frequency sound velocity is found to be of about 2150 m/s almost independently on temperature. The temperature dependence of the relaxation time is discussed and compared with that of other relaxation times available in the literature. Predictions are made for the temperature and wave vector values at which the dispersion of sound velocity should be best observed.

Neutron diffraction measurements on liquid ammonia at two temperature states on the liquid‐vapor coexistence curve are presented. Three isotropic mixtures of hydrogenated and deuterated ammonia have been studied and the three radial atom–atom distribution functions extracted at 213 K and 273 K. The comparison of the experimental results with the partial radial distribution functions for orientationally uncorrelated molecules, shows some evidence for hydrogen bonding in liquid ammonia but this is much less pronounced than that found in water under ambient conditions.

High resolution depolarized Raman spectra of n-pentanol in the - 30 to 60-degrees-C temperature range are reported. The spectra appear as a continuously decreasing line shape centered at zero frequency. A quantitative analysis of this line shape shows a high frequency exponential tail, which can safely be assigned to intermolecular collision phenomena, and a low frequency narrow contribution. The line shapes of the low frequency contribution are seen to deviate from a single Lorentzian, the effect being more pronounced as the temperature is increased. The data have been analyzed assuming the non-Lorentzian line shape as due either to a distribution of Debye relaxation times or to a single non-Debye relaxation mechanism. The analysis in terms of a distribution of relaxation times suggests a broadening of the distribution as the temperature increases, while the "average" relaxation time shows an Ahrenius behavior which compares well with the one observed in the ultrasonic attenuation measurements. Similar results have been obtained considering the nonexponential relaxation mechanisms. Absolute intensities are also evaluated with respect to the Brillouin doublet and discussed in terms of the possible microscopic scattering mechanisms.

Brillouin light scattering spectra from transverse and longitudinal acoustic waves in liquid and supercooled 3-methylpentane have been collected from room temperature down to 80 K, just above the glass transition. Spectra at different wave vectors have been obtained using 532 nm and 266 nm excitation. We found evidence of a shear relaxation with a characteristic time of 100 s at the glass transition which only partly accounts for the relaxation observed in the propagation and attenuation of the longitudinal modes. The inclusion of a relaxing bulk viscosity contribution with a relaxation time of the order of 10(2) ns at the glass transition is found to adequately reproduce the experimental data including transient grating data at a much lower frequency. A consistent picture of relaxed shear and bulk moduli as a function of temperature is derived. These two quantities are found to be related by a linear relation suggesting that a Cauchy-like relation holds also above the glass transition.

In this paper we present a comparative study of the agglomeration process in silicon-on-insulator (SOI), silicon germanium-om-insulator (SGOI), and strained SOI (SSOI) thin layers under thermal annealing in ultrahigh vacuum. In particular, we provide the first evidence and characterization of agglomeration in SGOI and SSOI substrates. A common agglomeration dynamics is observed in all the substrates investigated, with the semiconductor-on-insulator layer thickness being the main parameter governing it. These findings provide a better understanding of the surface-energy-driven dewetting phenomenon in semiconductor layers and allow us to single out the influence of the surface and stress energies on the void formation and evolution, as well as on the size and density of the agglomerated islands. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3117837]

Inelastic neutron scattering experiments were performed at intermediate and high momentum transfer, up to 88.2 A−1, to study the temperature dependence of single hydrogen mean kinetic energy in polycrystalline and liquid hydrogen sulphide (H2S), in the temperature range 16–206 K. Values of the hydrogen mean kinetic energy were extracted, within the impulse approximation, by fitting to the high momentum transfer data a model response function, obtained from a momentum distribution which is the orientational average of a multivariate Gaussian function. The extracted kinetic energies are compared with a harmonic model for the vibrational and roto-translational dynamics. The model makes use of the hydrogen-projected density of states worked out from intermediate momentum transfer data, as well as of optical frequencies determined from Raman and infrared (IR) spectroscopy. A fairly good agreement is obtained in the whole temperature range, while noticeably lower values for the kinetic energy are found if a sin...

A systematic extended x‐ray absorption fine structure (EXAFS) study of the structural parameters of the I2 molecule has been performed for I2 liquid, solid and in low density gaseous phases, as well as for I2 dissolved in organic solvents. Measurements on gaseous HI have also been performed in order to refine the structural analysis. A complex atomic double‐electron excitation background at the I K‐edge has been observed. A careful data analysis with full statistical evaluation of the results has indicated undoubtedly that, in condensed phases, the average bond length can increase by as much as 0.03 A with respect to the free molecule value. The expansion, known to occur from gas to liquid, and solid I2, was confirmed by the present EXAFS analysis while in the case of I2 in solution this is the first determination of the bond length. In particular we find that the bond length increases monotonically while decreasing the ionizing potential of the solute. A linear correlation between the blue‐shift of the o...