Surface Brillouin scattering

C.E. Bottani, A.L. Bassi, B.K. Tanner, A. Stella, P. Tognini, P. Cheyssac, R. Kofman, Melting in metallic Sn nanoparticles studied by surface Brillouin scattering and synchrotron-x-ray diffraction. Phys. Rev. B 59(24), 15601-15604 (1999)... 

The agreement between fee bulk modulus deduced from Brillouin scattering measurements and fee ADX results is very good. The determination of fee elastic moduli by ultrasonics was made by fee measurement of surface acoustic wave velocities on thin films [22], The second ultrasonics experiment was made on sintered powder, by measuring fee longitudinal and transverse sound velocity at ambient and under uniaxial compression. From feat, fee bulk modulus and its pressure derivative were deduced, but this result seems to be quite imprecise. The ultrasonics experiment on thin films gives rise to a very small difference in fee bulk modulus (5%), but fee ADX or Brillouin determination should be utilised for preference. 

Modem enhancement techniques enable the signal-to-noise ratio to be increased by interactions with surface plasmons (33) or surface effects (34). Inelastic tunneling spectroscopy (35), Brillouin scattering (36), and photoacoustic spectroscopy (37) have also been used to explore the vibrational modes in LB films. 

Vibration frequencies and phonon dispersion See Figs. 20 - 23. Table 13. Perpendicular vibration frequencies /zcoi and characteristics of the phonon dispersion curves for the noble gas monolayers. The sound velocities c/ and c, were obtained from the initial slope of the dispersion curves for the longitudinal (L) and shear-horizontal (SH) modes, respectively. Where complete or partial dispersion curves are available, oidy the value at the boundary of the surface Brillouin zone is indicated. Abbreviations used F, M, K high syrtunetry points of the 2D adlayer Brillouin zone (BZ) [001], [110] and [112] crystallographic directions of the substrate surface. All data were obtained using inelastic He-atom scattering. (Ad. = adsorbate) ... 

Fig. 2 Normalized dispersion relation for pSi superlattiees showing composite data from large set of superlattice samples obtained by Brillouin scattering experiments. The solid dashed) curves are theoretical longitudinal (transverse) modes obtained from the Rytov model. The horizontal hne identifies a locahzed surface mode lying within die phononic bandgap of the bulk longitudinal mode, trapped at the surface of the phononic crystal. Full details of die samples and acoustic branch identification in Parsons and Andrews (2012) (Reprinted with permission from Journal of applied physics by American Institute of Physics, Copyright 2012, American Institute of Physics)...

The density and SAXS measurements on the sanple treated at 900°C show a small residual porosity with large pore size (6 nm) and indeed small internal surface area. Low temperature specific heat and Brillouin scattering measurements confirm the Raman results. Important specific heat excess is observed for temperatures lower than about 5 Kin the non-densified xerogels, whereas the specific heat of the sanple annealed at 900°C is identical to that ofv-SiOi (Caponi, 2002). 

The following elastic constants Cy for room temperature have been derived from ultrasound measurements by Boppart et al. [11], [12, p. 108], [13], from phonon data (neutron scattering) by Mook, Holtzberg [17], and Brillouin scattering (sound velocity difference between bulk and surface) by Barth, GCintherodt [18]. The earlier data of Ott etal. [14] for c and c 2 are calculated from the bulk modulus K = (Cn + 2ci2)/3 = 5.1 ( 510 kbar) and (c -Ci2)/2 = 5.2 (for TmSe with a = 571 A). 

As an optical technique, Brillouin scattering allows the determination of the elastic constants and hence of the bulk moduli through the interaction of light with thermal excitation in a material, in particular acoustic phonons in a crystal. In this technique, the elastic constants Cn and Cgg can be directly obtained from measurement of the phase velocity of the longitudinal mode and of the shear horizontal mode traveling parallel to the crystal surface. The remaining constants,... 

---