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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2818-2824 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Propagation of surface acoustic modes on the (001) and (111) surfaces of Si coated by a thin isotropic overlayer is studied theoretically and experimentally. It is shown that when a surface acoustic wave (SAW) coexists with a pseudosurface wave (PSAW) of the uncoated substrate, the second-order acoustic mode of the film/substrate system originates from a PSAW and the first-order one from a SAW. The polarization pattern of either mode varies from Rayleigh type (saggital plane polarization) to Love type (horizontal polarization) depending on the propagation direction and the product of the wave vector q and film thickness d. It is also shown that the isolated off-symmetry pure mode point within the PSAW branch disappears at some critical qd value. Experimentally, surface acoustic modes of Ti-coated Si wafers are measured with the impulsive stimulated thermal scattering (ISTS) technique based on laser generation and detection of acoustic waves at a specified wave vector. ISTS data are shown to be determined by the surface elastodynamic Green function G13(ω,g). The measurements, only sensitive to Rayleigh-type waves, detect either the first- or the second-order mode, or both, depending on the qd and the observation angle. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5266-5269 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A simple dispersion equation for surface thermal waves propagating along a solid surface covered with a thin film of higher thermal conductivity is presented. It is shown to describe well phase measurements with a photothermal microscope carried out on metal films on glass substrates. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6052-6054 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Shake-off of micron-sized alumina particles by nanosecond laser-generated surface acoustic wave (SAW) pulses is used to visualize SAW beam propagation on surfaces of semiconductor crystals. Various phenomena in SAW propagation such as reflection from a sample edge, anisotropic diffraction, and beam steering are demonstrated. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1344-1346 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A transient grating technique is used to detect picosecond acoustic pulses in supported metal films. Crossed femtosecond laser pulses generate acoustic responses with longitudinal components propagating normal to the film plane and surface acoustic wave components propagating in the film plane. Surface "ripple" associated with both components is detected through the diffraction of a probe beam. The measurements yield enhanced information content for characterization of film thickness and mechanical properties. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5082-5085 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Transient surface displacement of gold under femtosecond laser irradiation is studied using a probe beam deflection technique. A surface thermal expansion rise time of about 100 ps is explained in terms of nonequilibrium diffusion and thermalization of photoexcited electrons. Transient displacement provides direct information on the lattice temperature profile established once the electron-lattice relaxation is completed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 35 (2003), S. 429-439 
    ISSN: 1434-6036
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract. Strong anisotropic effects in the propagation of surface acoustic waves (SAWs) from a point-like source are studied experimentally and theoretically. Nanosecond SAW pulses are generated by focused laser pulses and detected with a cw probe laser beam at a large distance from the source compared to the SAW wavelength, which allows us to resolve fine intricate features in SAW wavefronts. In our theoretical model, we represent the laser excitation by a localized impulsive force acting on the sample surface and calculate the far-field surface response of an elastically anisotropic solid to such a force. The model simulates the measured SAW waveforms very well and accounts for all experimentally observed features. Using the data obtained for the (111) and (001) surfaces of GaAs, we describe a variety of effects encountered in the SAW propagation from a point source in crystals. The most interesting phenomenon is the existence of cuspidal structures in SAW wavefronts resulting in multiple SAW arrivals for certain ranges of the observation angle. Cuspidal edges correspond to the “phonon focusing” directions yielding sharp peaks in the SAW amplitude. A finite SAW wavelength results in “internal diffraction” whereby the SAW wavefront spreads beyond the group velocity cusps. Degeneration of a SAW into a transverse bulk wave is another strong effect influencing the anisotropy of the SAW amplitude and making whole sections of the SAW wavefront including some phonon focusing directions unobservable in the experiment. The propagation of a leaky SAW mode (pseudo-SAW) is affected by a specific additional effect i.e. anisotropic attenuation. We also demonstrate that many of the discussed features are reproduced in “powder patterns”, a simple technique developed by us earlier for visualization of SAW amplitude anisotropy.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1432-0630
    Schlagwort(e): 07.20.−n ; 44.10.+i ; 44.30.+v
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Transient Thermal Gratings (TTGs) at surfaces of absorbing materials have been utilized for investigating heat diffusion in bulk materials and thin films. In this report, we describe the theoretical background of the technique and present experimental data. TTGs were excited in the surface plane by interference of two pulsed laser beams and monitored by a cw probe beam, either via temperature dependence of the reflectivity or by deflection from the displacement pattern. A theoretical model describing the thermal and thermoelastic surface response was developed, both for a homogeneous material and a multilayer structure. The potential of the technique will be demonstrated by experimental results on (i) thermal diffusivities of bulk materials, (ii) anisotropic lateral heat transport, and (iii) thermal diffusivities of metal and diamond films. Furthermore, we will show that TTGs allow thermal depth profiling of inhomogeneous materials whenever there is a vertical gradient in thermal conductivity.
    Materialart: Digitale Medien
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