Acoustic anisotropy in uniaxial tungsten bronze ferroelectric single crystals studied by Brillouin light scatteringIn an effort to reduce RC time delays that accompany decreasing feature sizes, low-k dielectric films are rapidly emerging as potential replacements for silicon dioxide ͑SiO 2 ͒ at the interconnect level in integrated circuits. The main challenge in low-k materials is their substantially weaker mechanical properties that accompany the increasing pore volume content needed to reduce k. We show that Brillouin light scattering is an excellent nondestructive technique to monitor and characterize the mechanical properties of these porous films at thicknesses well below 200 nm that are pertinent to present applications. Observation of longitudinal and transverse standing wave acoustic resonances and the dispersion that accompany their transformation into traveling waves with finite in-plane wave vectors provides for a direct measure of the principal elastic constants that completely characterize the mechanical properties of these ultrathin films. The mode amplitudes of the standing waves, their variation within the film, and the calculated Brillouin intensities account for most aspects of the spectra. We further show that the values obtained by this method agree well with other experimental techniques such as nanoindentation and picosecond laser ultrasonics.

We report on a Brillouin light scattering study of acoustic excitations in free-standing polymethyl methacrylate ͑PMMA͒ /Si 3 N 4 double layer membranes. For vanishing-wave vector transfer along the membrane, the observed excitations are a series of longitudinal standing wave harmonics whose frequencies depend on PMMA and Si 3 N 4 layer thickness. The associated displacement profiles below 30 GHz are largely confined to the softer PMMA layer with mode amplitudes significantly higher at the PMMA surface than at the free surface of the high elastic modulus Si 3 N 4 layer. At higher frequencies, in the vicinity and beyond the resonance associated with the Si 3 N 4 layer, the mode amplitudes become comparable at both free surfaces. Excitations with transverse polarization as well as waves whose amplitudes within the Si 3 N 4 are consistent with flexural and dilatational modes for a single layer are also observed. For certain ranges of wave vector the latter interact and hybridize with the harmonics arising from the PMMA layer.

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Brillouin light scattering investigations of acoustic vibrations in freestanding membranes, soft-hard bi-layers and patterned wires are described. Studies of longitudinal and transverse standing wave resonances, the wave vector dependence of surface and guided waves as well as their hybridization with flexural and dilational waves are presented. Size effects and the role of reduced dimensions on the acoustic behavior are investigated in soft rectangular polymeric wires on freestanding silicon nitride membranes. The mode frequencies and amplitudes are analyzed in terms of surface Green's functions and the xyz algorithm.

We report room temperature Brillouin light scattering measurements designed to probe the elastic properties of chemically ordered Co3Pt alloy films. A series of 100 nm thick films were deposited by molecular beam epitaxy at different growth temperatures (Tg) between 450 and 950 K. As the deposition temperature increases the lattice structure is observed to transform from a compositionally disordered, mixed fcc/hexagonal phase to a compositionally ordered, purely hexagonal phase, and finally to a compositionally disordered fcc phase. These structural transitions are accompanied by large changes in magnetic anisotropy, new features in the magneto-optical Kerr effect, and changes in the magnetic domain widths which all occur within about a 100 K temperature window centered around Tg=650 K. However, the independent elastic constants show no significant changes in the different films. These findings suggest that macroscopic strain effects are unlikely to underlie the diverse magnetic signatures observed within the chemically ordered phase.