Surface Brillouin scattering of opaque solids and thin supported films

Surface Brillouin scattering (SBS) has been used successfully for the study of acoustic excitations in opaque solids and thin supported films, at both ambient and high temperatures. A number of different systems have been investigated recently by SBS including crystalline silicon, amorphous silicon layers produced by ion bombardment and their high temperature recrystallisation, vanadium carbides, and a nickel-based superalloy. The most recent development includes the measurement of a supported gold film at high pressure. The extraction of the elastic constants is successfully accomplished by a combination of the angular dependence of surface wave velocities and the longitudinal wave threshold within the Lamb shoulder. The application of surface Green's function methods successfully reproduces the experimental SBS spectra. The discrepancies often observed between surface wave velocities and by ultrasonics measurements have been investigated and a detailed correction procedure for the SBS measurements has been developed.     

Harmonic ion acoustic waves in stimulated Brillouin scattering

Ion acoustic harmonic generation is a heavy damping mechanism of stimulated Brillouin scattering. The theory of first harmonic ion wave production is extended to frequencies four times the fundamental. Besides, the corresponding set of 6 differential equations is solved numerically for the steady state, and spatial solutions of the ion wave amplitudes are obtained. By varying typical parameters of laser plasma interaction experiments some characteristics properties are gained which might be of use for comparison with experiments.     

Brillouin scattering study on the wave properties in thin SiC films

The modified Rayleigh wave velocities on the SiC hetero-epitaxial films have been investigated using a Brillouin scattering technique. The SiC nanoscopic films were formed on clean surface of Si substrates by the molecular ion beam technique or Ion beam induced chemical vapor deposition. Back scattering geometry was used to obtain the ripple Brillouin scattering from the film surface. Owing to the high stability of the measurement system, the precise velocity measurement was performed. As a result, Rayleigh wave velocity showed a clear dependence on the crystalline structure of SiC film, indicating that the shear moduli of very thin epitaxial films shows similar tendency with those of SiC bulk sample.     

Reduction of guided acoustic wave Brillouin scattering in photonic crystal fibers

Guided acoustic wave Brillouin scattering (GAWBS) generates phase and polarization noise of light propagating in glass fibers. This excess noise affects the performance of various experiments operating at the quantum noise limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic crystal fiber in a broad frequency range by tailoring the acoustic modes using the photonic also as a phononic crystal. We compare the noise spectrum to the one of a standard fiber and observe a tenfold noise reduction in the frequency range up to 200 MHz. Based on our measurement results as well as on numerical simulations, we establish a model for the reduction of GAWBS noise in photonic crystal fibers.     

Temperature dependence of the interaction between surface acoustic waves and nickel thin films

Measurements of the magnetic-field-dependent attenuation of 618-MHz surface acoustic waves by a 500-Å nickel film, made over the temperature range 4–350 K, are reported. Some room-temperature hysteresis-dependent interactions are also described.     

Phase-sensitive acoustic microscopy of polymer thin films

The three-dimensional images obtained by scanning acoustic microscopy with vector contrast (PSAM), contain significant qualitative and quantitative information that is not easily obtainable by other methods. We employ this technique to examine homopolymer and polymer blend thin films. The complex V(z) functions derived from the images, and the results obtained by image processing and meticulous analysis are employed to render the morphology, composition and micro-mechanical properties of the polymer films. In addition, ways by which the information inherent in the phase images can be extracted are examined. This is highly desirable, as the phase images contain very useful additional information.     

Brillouin scattering study of multilayer cobalt-niobium films

Spin waves which are characteristic of periodic structures of thin ferromagnetic Co films alternating with nonmagnetic Nb films have been investigated by means of Brillouin light scattering. The dependence of the magnon frequencies on the magnetic inplane field and on the wave-vector was measured for several samples with different numbers and thicknesses of the layers. The experimental data are in good agreement with a theory of magnetostatic surface spin waves in such media elaborated by Grünberg and Mika. The amplitudes of the transverse magnetization in the different layers of the stack have been calculated. The highest frequency branch resembles the Damon-Eshbach surface magnon. With decreasing frequency the branches acquire volume mode character. In addition, a number of phonon branches has been observed which are interpreted as plate modes of the combined Co-Nb layer on the Si substrate.     

Brillouin light scattering characterization of the surface acoustic wave velocity in sp<Superscript>2</Superscript> allotropes thin films

Carbon thin films have been deposited by DC magnetron sputtering at different substrate temperatures ranging from 200 K to 400 K. The influence of the preparation substrate temperature on the elastic properties has been evidenced by means of the High Resolution Brillouin Spectroscopy. Thus, the surface acoustic wave (SAW) velocity evolution could be assessed for the different samples. The observed variation is analysed in terms of the relative population of sp² allotropes phases forming the film.     

Surface acoustic waves and elastic constants of InN epilayers determined by Brillouin scattering

The surface acoustic wave velocity in InN has been experimentally determined by means of Brillouin scattering experiments on c ‐ and m ‐face epilayers. From simulations based on the Green's function formalism we determine the shear elastic constants c₆₆ and c₄₄ and propose a complete set of elastic constants for wurtzite InN. The analysis of the sagittal and azimuthal dependence of the surface acoustic wave velocity indicates a slightly different elastic behavior of the m ‐face sample that basically affects the c₄₄ elastic constant. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Light scattering study of surface plasmon resonances in very thin silver films

The surface plasmon modes of Ag thin films were studied by the light scattering method in the thickness range down to 100 Å. The observed thickness dependence of the resonance peaks was analysed in detail by the theory of Kretschmann. It is shown that the coupled surface plasmon modes in the very thin films can be detected only in modified forms by the light scattering experiment.     

Calculations of TM-polarized nonlinear waves guided by thin dielectric films

We found the dispersion relations for TM-polarized nonlinear waves guided by a dielectric film of thicknessd bounded on one side by a nonlinear uniaxial medium characterized by a dielectric tensor _xx = _y = _c , _zz = _c + _c |E _z |², _c >0 (self-focusing medium),E _z being the electric-field component perpendicular to the surfaces. Numerical calculations are given for the power dependence of the propagation wave vector. For sufficiently larged/ (: wavelength) we have found regions with multiple solutions corresponding to the same power flow. This suggests possible applications to optical devices.     

Detection of surface acoustic waves by scanning tunneling microscopy

A new method for the investigation of ultrasonic waves on surfaces of solids based on scanning tunneling microscopy is presented. A sinusoidal high frequency signal is added to the tip voltage. Hence the tunneling current contains a component whose frequency is the difference of the frequencies of the acoustic wave field and the ac tip voltage. Amplitude and phase of this component carry the full information about the wave field.     

Temperature and strain sensitivities of surface and hybrid acoustic wave Brillouin scattering in optical microfibers

Temperature and strain sensitivities of surface acoustic wave (SAW) and hybrid acoustic wave (HAW) Brillouin scattering (BS) in 1 μm-1.3 μm diameter optical microfibers are simulated. In contrast to stimulated Brillouin scattering (SBS) from bulk acoustic wave in standard optical fiber, SAW and HAW BS, due to SAWs and HAWs induced by the coupling of longitudinal and shear waves and propagating along the surface and core of microfiber respectively, facilitate innovative detection in optical microfibers sensing. The highest temperature and strain sensitivities of the hybrid acoustic modes (HAMs) are 1.082 MHz/℃ and 0.0289 MHz/με, respectively, which is suitable for microfiber sensing application of high temperature and strain resolutions. Meanwhile, the temperature and strain sensitivities of the SAMs are less affected by fiber diameter changes, ranging from 0.05 MHz/℃/μ to 0.25 MHz/℃/μ and 1×10^-4 MHz/με/μ to 5×10^-4 MHz/με/μ, respectively. It can be found that that SAW BS for temperature and strain sensing would put less stress on manufacturing constraints for optical microfibers. Besides, the simultaneous sensing of temperature and strain can be realized by SAW and HAW BS, with temperature and strain errors as low as 0.30 ℃-0.34 ℃ and 14.47 με-16.25 με.     

An experimental study of forward and backward scattering of acoustic waves from a thin bubble layer

Forward and backward scattering of acoustic signals from a thin chaotic bubble screen is studied experimentally. The concentration of inhomogeneities in the bubble layer is estimated by an acoustic method, and the presence of collective scattering effects is revealed. The transverse correlation radius of the scattered field amplitude is determined, and its value is used to estimate the correlation scales of inhomogeneities in the bubble layer.     

Polymer thin films and surfaces: Possible effects of capillary waves

It is discussed how the proximity of a free surface or mobile interface may affect the strain relaxation behavior in a viscoelastic material, such as a polymer melt. The eigenmodes of a viscoelastic film are thus derived, and applied in an attempt to explain the experimentally observed substantial shift of the glass transition temperature of sufficiently thin polymer films with respect to the bulk. Based on the idea that the polymer freezes due to memory effects in the material, and exploiting results from mode-coupling theory, the experimental findings of several independent groups can be accounted for quantitatively, with the elastic modulus at the glass transition temperature as the only fitting parameter. The model is finally applied discussing the possibility of polymer surface melting. A surface molten layer is predicted to exist, with a thickness diverging as the inverse of the reduced temperature. A simple model of thin polymer film freezing emerges which accounts for all features observed experimentally so far. Received 8 August 2001     

Reflection and mode conversion of surface acoustic waves studied by scanning acoustic force microscopy

We present measurements of the reflection and mode conversion of surface acoustic waves (SAWs) by scanning acoustic force microscopy (SAFM). The SAFM offers a unique combination of high lateral resolution and high sensitivity towards acoustic modes of all polarizations. Since a SAW mixing experiment of two waves can be performed even if the amplitude difference between both waves is 40 dB, wavefields of extremely small amplitudes can be investigated. Using SAFM, the reflection of SAWs from a metallic wedge is investigated with submicron lateral resolution. We are able to identify two reflected wave modes, a Love and a non-coupling Rayleigh mode, by measuring their phase velocities. Received: 4 December 2000 / Accepted: 6 December 2000 / Published online: 9 February 2001     

Visualization of inverse phase velocity surfaces of bulk and surface acoustic waves

Diffraction of light by ultrasound has been used to study complete cuts of the inverse phase velocity surfaces for both bulk and surface acoustic waves in lithium niobate.