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Superlattice thin films are expected to show elastic anisotropy because of lattice misfits at interfaces among different elements. This study demonstrates that resonant-ultrasound spectroscopy and laser-Doppler interferometry can determine anisotropic elastic constants of superlattice thin films. Mechanical resonance frequencies of a layered specimen composed of a substrate and deposited thin film depend on the elastic constants, mass densities, and dimensions of the substrate and thin film. X-ray diffraction measurement determines accurately the total thiskness of a multilayer thin film. Therefore, the elastic constants of the multilayer thin film can be derived from measured resonance frequencies, provided that mode identification on observed resonance frequencies is achieved. We measure the resonance frequencies by a piezoelectric tripod and identify the vibration modes by measuring the displacement distributions on the specimen surface using laser-Doppler interferometry. We apply the present method to a Co/Pt multilayer [Co(4 Å)/Pt(16 Å)]500 showing the perpendicular magnetic anisotropy. The in-plane elastic constants are larger than those of bulks by 1%–7%. This is attributed to internal strain due to lattice misfit at the Co–Pt interfaces through interatomic anharmonicity. [ABSTRACT FROM AUTHOR]

This article studies elastic anisotropy of chemical vapor deposition (CVD) polycrystalline diamond films using acoustic spectroscopy and micromechanics modeling. CVD diamond films often exhibit elastic anisotropy between the film-growth direction and in-plane direction and show five independent elastic constants. They are denoted by C[sub 11], C[sub 33], C[sub 13], C[sub 44], and C[sub 66] when the x[sub 3] axis lies along the film-growth direction. Measurements of thickness resonance frequencies and free-vibration resonance frequencies of the diamond film deduce four independent elastic constants among them, including C[sub 44] and C[sub 66], with which the elastic anisotropy is discussed. The anisotropy between the shear moduli is 5%–10%. The elastic constants are remarkably smaller than those of an isotropic polycrystalline diamond. We attribute the anisotropy and small elastic constants of the CVD diamond film to local incomplete cohesion. This view is supported by a micromechanics calculation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article introduces an advanced acoustic method for measuring the out-of-plane longitudinal-wave modulus of thin films using picosecond ultrasound. The ultrafast light pulse is focused on the film surface to excite the coherent acoustic pulse, which propagates in the thickness direction, and then, the time delayed probing light pulse irradiates the specimen for detecting the acoustic waves. For opaque thin films, the pulse echoes within the film or the thickness resonance frequency of the film is measured to determine the modulus. For transparent films, Brillouin oscillations from the film are observed, and their frequencies yield the modulus. The film thickness and refractive index are measured by X-ray reflectivity and ellipsometry, respectively. This method was applied to various thin films, providing important knowledge about the elasticity of thin films. Most thin films are softer than corresponding bulk materials, but some thin films are significantly stiffer. [ABSTRACT FROM AUTHOR]

We propose an advanced method to determine the elastic-stiffness coefficients Cij of thin films using resonance ultrasound spectroscopy (RUS). It uses free-vibration resonance frequencies of a film/substrate layered solid and derives inversely the film’s Cij from the resonance frequencies. We develop a piezoelectric tripod consisting of two pinducers and one support to place the specimen on it and measure the resonance frequencies with high enough accuracy. Furthermore, we achieve mode identification by measuring deformation distributions on the vibrating specimen surface using laser-Doppler interferometry. Accurate measurements of frequencies and correct mode identification are the keys for deducing reliable Cij of the film. We applied this technique to copper thin films deposited of Si substrates. The resulting film’s Cij are considerably smaller than the bulk’s Cij and show anisotropy between the out-of-plane direction and in-plane direction. [Copyright &y& Elsevier]

Polycrystalline thin films show transverse isotropy (or hexagonal symmetry) and show five independent elastic constants because of columnar structure, texture, residual stress, and local incohesive bonds (or microcracks). In this paper, we developed an advanced method for measuring the anisotropic elastic constants of thin films using resonance ultrasound spectroscopy and determined the elastic constants of chemical-vapor-deposition diamond thin films. Mechanical resonance frequencies of a film/substrate layer specimen were measured, from which elastic constants of the thin film were determined by an inverse calculation. Mode identification for observed resonance frequencies is the key for their successful determination. We achieved this by measuring the displacement distribution on the vibrating-specimen surface. Determined elastic constants are smaller than those of bulk diamond, and they are elastically anisotropic between in-plane and out-of-plane directions. We attribute these compliant and anisotropic thin films to the incohesive bond at grain boundaries. A micromechanics model consistently explains the observation. [Copyright &y& Elsevier]

This letter studies the relationship between the off-diagonal elastic constant C12 and bond configuration in nanocrystalline-diamond (NCD) thin films deposited by the nitrogen-doped chemical vapor deposition method. The film thickness was varied between 2.4 and 11.3 μm. The elastic constants were measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The diagonal elastic constants C11 and C44, and Young’s modulus in NCD films are smaller than those of the bulk polycrystalline diamond and microcrystalline-diamond (MCD) thin films, and they decrease as the film thickness decreases. However, the off-diagonal elastic constant of the NCD films is significantly larger than that of the bulk diamond, while that of the MCD films is smaller. Micromechanics calculations revealed that this exceptional enhancement of C12 occurs when the material includes randomly distributed thin graphitic plates in the isotropic diamond matrix. Thus, this result indicates that the NCD films consist of sp3-bonded diamond grains and sp2-bonded grain boundaries. [ABSTRACT FROM AUTHOR]

This study is devoted to a correlation between elastic constants and magnetic anisotropy of Co/Pt superlattice thin films. Co/Pt superlattice thin films with various Co–Pt layer wavelengths were deposited on monocrystal silicon substrates by an ultrahigh-vacuum-evaporation method, keeping the volume fractions of the Co and Pt layers unchanged. Their perpendicular magnetic anisotropy ranged between -0.2 and 5.0 MJ/m3. Resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry determined their hexagonal-symmetry elastic constants, which correlate with the magnetic anisotropy; higher perpendicular magnetic anisotropy causes larger in-plane elastic moduli and smaller out-of-plane moduli. The correlation is explained by internal elastic strain associated with lattice misfit at the Co–Pt interfaces. [ABSTRACT FROM AUTHOR]

Abstract: Novel thin-film oscillator biosensors are developed using picosecond ultrasound method. 100-nm silicon-nitride thin films and 16-nm Pt thin films are used, and ultrashort light pulses are focused on their surfaces to excite the through-thickness resonance vibrations, which are detected by the delayed probe-light pulses using the optoelastic effect. Their fundamental resonance frequencies are 45 and 132GHz, corresponding to theoretical mass sensitivities of 5.0×10−5 and 2.2×10−5 pg/cm2/Hz, respectively. These thin-film biosensors are used for detecting human immunoglobulin G (hIgG) with staphylococcus aureus protein A nonspecifically immobilized on the film surfaces. Injection of a 5nM analyte caused 2% decrease in the resonance frequency. [ABSTRACT FROM AUTHOR]