Laser Doppler Interferometry Research Articles

Relationship between Elastic Constants and Microstructure of Nanocrystalline CVD Diamond Thin Films

This paper studies the relationship between elastic constants and microstructure of chemical vapor deposition (CVD) diamond thin films deposited by the hot-filament CVD method with a small amount of N2 impurities for decreasing the grain size. The size is of the order of 10 nm, which we call nanocrystalline diamond (NCD). The N2 flow rate was 0.0-1.0 sccm and the film thickness was about 12μm. Three elastic constants C11, C12, and C66 were measured by resonant ultrasound spectroscopy coupled with laser-Doppler interferometry (RUS/LDI). The diagonal elastic constants, C11, C66, and E1 of CVD diamond thin films decrease with the increase of the N2 flow rate. However, the off-diagonal elastic constant C12 increases with the increase of the N2 flow rate. The micromechanics model we propose consistently explains the enhancement of C12 when thin pancake-shaped graphite inclusions on the grain boundaries are introduced, whose c axes are oriented along the minor direction randomly distributed in isotropic diamond matrix. Thus, this result indicates that oriented graphitic phase exists at the grain boundaries in NCD films.

The Strain Response of Lead Zinc Niobate-Lead Titanate Piezocrystals: Phase Transitions and Non-Linear Effects

Single crystals of Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 (PZN-PT) produce high levels of strains with large electromechanical coupling coefficients and they exhibit high dielectric permittivity. These properties make PZN-PT single crystals promising materials for transducer and actuator applications. The large strains in these materials are partly due to electric-field-induced rhombohedral–tetragonal phase transitions that are temperature dependent. We have studied the phase transitions in ⟨001⟩ oriented Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 single crystals for x = 4.5% and x = 8% by measuring the piezoelectric strains of the crystals as a function of applied electric field and temperature. We have used laser Doppler interferometry to make direct measurements of the strain responses of the two types of ⟨001⟩ and ⟨111⟩ oriented PZN-PT single crystals in the rhombohedral phase as a function of AC electric fields and DC bias fields. When the applied electric field exceeds a threshold value, the dielectric and piezoelectric constants become a function of the applied field, and hysteresis loops are observed. Our results show that a positive DC bias stabilizes the domain configuration in the crystals and increases the range of AC voltages over which the response is linear. The threshold field, at the onset of non-linearity, is found to have a linear relation with DC bias field in the field range investigated. Very large shear strains have been observed for crystals poled in the pseudocubic ⟨111⟩ direction with d 15 values in the neighbourhood of ∼5500 pC/N for PZN-4.5%PT and ∼7500 pC/N for PZN-8%PT.

Acoustic Study of Martensitic Phase Transformation in TiNbAl Shape Memory Alloy

Martensitic phase transformation from the β to the α'' phase (and vice versa) in a TiNbAl alloy system has been studied by ultrasound spectroscopy. Resonance frequencies and corresponding internal frictions are measured from ambient temperature to 12 K by electromagnetic acoustic resonance (EMAR) and resonant ultrasound spectroscopy (RUS) coupled with laser Doppler interferometry. Both in the cooling and heating processes, we observed a marked decrease in resonance frequency and an increase in internal friction approaching the transformation temperatures. The analysis of temperature dependence in the elastic moduli indicates that lattice anharmonicity in the longitudinal acoustic mode may play a dominant role in the martensitic phase transformations.

Off-diagonal elastic constant and sp2-bonded graphitic grain boundary in nanocrystalline-diamond thin films

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 11.3μm. 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.

Back to Basics. Optical Methods in Experimental Mechanics. Part 17: Laser Doppler Interferometry

Back to Basics. Optical Methods in Experimental Mechanics. Part 17: Laser Doppler Interferometry

Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin films

ABSTRACTThis paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in‐plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement–amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions.

Elastic constants and magnetic anisotropy of Co∕Pt superlattice thin films

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 5.0MJ∕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.

Ｃｏ／Ｐｔ超格子薄膜の弾性定数のひずみ依存性と磁気異方性

In this paper, the contribution of magnetoelastic-anisotropy effect on perpendicular-magnetic anisotropy of Co/Pt superlattice thin films is studied considering the strain-dependent elastic constants. We measured the effective-magnetic-anisotropy energy changing the Pt-layer thickness (2 to 20 A) keeping the Co-layer thickness unchanged (4 A). The effective-magnetic-anisotropy energy changed depending on the Pt-layer thickness and showed a maximum near dPt=12 A. This result is explained by calculating the magnetoelastic-anisotropy energy considering the change of the elastic constants caused by the lattice misfit. We measured anisotropic elastic constants of Co/Pt superlattice thin films by resonance-ultrasound-spectroscopy method coupled with laser-Doppler interferometry and the picosecond laser-ultrasound method. The measured elastic constants showed elastic anisotropy between the in-plane and out-of-plane directions. They agreed with those predicted from the strain-dependent elastic-constant model. The elastic constants show correlations with the perpendicular-magnetic anisotropy.

Elastic Constants and Graphitic Grain Boundaries of Nanocrystalline CVD-Diamond Thin Films: Resonant Ultrasound Spectroscopy and Micromechanics Calculation

AbstractUsing resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry, we determine the independent elastic constants of nanocrystalline CVD-diamond thin films with thickness between 2-12 μm. They are deposited on oriented monocrystal silicon substrates by the hot-filament methane/nitrogen CVD method. The diagonal components of the elastic constants are smaller than those of microcrystalline CVD diamond films and bulk diamond. However, the off-diagonal component is larger. We attribute these observations to the presence of sp2-bonded graphitic phase at grain boundaries. A micromechanics model assuming inclusions of thin graphitic plates consistently explains the observations.

917 超音波共振/レーザー法によるナノ結晶ダイヤモンド薄膜の弾性定数測定と欠陥評価(GS-3,16 薄膜(2),研究発表講演)

We measured the elastic constants of nanocrystalline-diamond (NCD) thin films and microcrystalline-diamond (MCD) thin films deposited on a silicon substrate by the chemical-vapor-deposition (CVD) method using resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The elastic constants of the diamond thin films are smaller than those of a bulk diamond and the elastic constants of the NCD films are smaller than those of the MCD films. The elastic constants of the NCD film show a thickness dependence; thinner NCD films show smaller moduli. We attribute the elastic constants to incohesive bonds at grain boundaries and presence of thin graphite and amorphous diamond phases, which are suggested by Raman spectroscopy. The modified elastic constants are explained by a micromechanics modeling.

Advanced Resonant-Ultrasound Spectroscopy for Studying Anisotropic Elastic Constants of Thin Films

AbstractThis paper presents two advanced acoustic methods for the determination of anisotropic elastic constants of deposited thin films. They are resonant-ultrasound spectroscopy with laser-Doppler interferometry (RUS/Laser method) and picosecond-laser ultrasound method. Deposited thin films usually exhibit elastic anisotropy between the film-growth direction and an in-plane direction, and they show five independent elastic constants denoted by C11,C33,C44,C66 and C13 when the x3 axis is set along the film-thickness direction. The former method determines four moduli except C44, the out-of-plane shear modulus, through free-vibration resonance frequencies of the film/substrate specimen. This method is applicable to thin films thicker than about 200 nm. The latter determines C33, the out-of-plane modulus, accurately bymeasuring the round-trip time of the longitudinal wave traveling along the film-thickness direction. This method is applicable to thin films thicker than about 20 nm. Thus, combination of these two methods allows us to discuss the elastic anisotropy of thin films. The results for Co/Pt superlattice thin film and copper thin film are presented.

Determination of anisotropic elastic constants of superlattice thin films by resonant-ultrasound spectroscopy

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(4Å)∕Pt(16Å)]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.

Epithelial internalization of superparamagnetic nanoparticles and response to external magnetic field

Superparamagnetic magnetite nanoparticles (MNP) coated with silica were synthesized and chronically implanted into the middle ear epithelial tissues of a guinea pig model (n=16) for the generation of force by an external magnetic field. In vivo limitations of biocompatibility include particle morphology, size distribution, composition and mode of internalization. Synthesis of MNP was performed using a modified precipitation technique and they were characterized by transmission electron microscopy, X-ray diffractometry and energy dispersive spectroscopy, which verified size distribution, composition and silica encapsulation. The mechanism for internalizing 16±2.3nm diameter MNP was likely endocytosis, enhanced by magnetically force. Using sterile technique, middle ear epithelia of tympanic membrane or ossicles was exposed and a suspension of particles with fluoroscein isothiocyanate (FITC) label applied to the surface. A rare earth, NdFeBo magnet (0.35T) placed under the animal, was used to pull the MNP into the tissue. After 8 days, following euthanasia, tissues were harvested and confocal scanning laser interferometry was used to verify intracellular MNP. Displacements of the osscicular chain in response to an external sinusoidal electromagnetic field were also measured using laser Doppler interferometry. We showed for the first time a physiologically relevant, biomechanical function, produced by MNP responding to a magnetic field.

The Effect of Slider Texture on the Tribology of Near Contact Recording Sliders

Island-type texture was fabricated on two types of pico-sliders using plasma etching and ion beam etching. Laser–Doppler interferometry was used to investigate the vibrations of textured and untextured pico-sliders in near-contact situations. Lubricant depletion on the disk surface was investigated in the slider “wear tracks” using scanning ellipsometry (Surface Reflectance Analyzer (SRA)). The results show that slider in-plane and out-of-plane vibrations were reduced as a consequence of the texture on the slider surface. In addition, lubricant depletion on the disk surface was found to be less severe for textured sliders than for untextured sliders at flying heights below 10 nm.

Interface delamination of layered media: acoustic spectroscopy and modal analysis.

We have developed a method of resonance ultrasound spectroscopy (RUS) to study the acoustic spectral response to interface delamination in a triple-layered rectangular parallelepiped [Al(aluminum)/polymer/Al]. Combination of laser-Doppler interferometry and the Rayleigh-Ritz approximation affected mode identification in the measured resonance spectrum. Point-contact RUS is capable of sensing a minute delamination (1.5% of total area). Modal analysis using a number of resonance modes can deduce the delamination area and location in the interface. Not only screening but also defect characterization is possible. At the same time, some resonance modes are totally insensitive to an interface imperfection. These modes are found to have virtually no strain energy arising from the bonding layer.

Resonance ultrasound spectroscopy with laser-Doppler interferometry for studying elastic properties of thin films

We propose an advanced method to determine the elastic-stiffness coefficients C ij 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 C ij 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 C ij of the film. We applied this technique to copper thin films deposited of Si substrates. The resulting film’s C ij are considerably smaller than the bulk’s C ij and show anisotropy between the out-of-plane direction and in-plane direction.

Determination of elastic, anelastic, and piezoelectric coefficients of piezoelectric materials from a single specimen by acoustic resonance spectroscopy

We describe an advanced methodology to determine all the independent elastic-stiffness coefficients C ijkl , the associated internal frictions Q ijkl −1, and piezoelectric coefficients e ijk of piezoelectric materials from a single monocrystal specimen using resonant-ultrasound spectroscopy with laser-Doppler interferometry. The mechanical-resonance frequencies of a piezoelectric solid depend on all of the elastic and piezoelectric coefficients, and their accurate measurement allows one to determine the elastic and piezoelectric coefficients simultaneously. Resonance-peak-width measurements yield the internal-friction tensor. Successful determination requires correct vibration-mode identification for the observed resonance frequencies. This is achieved unambiguously by measuring deformation distributions on the vibrating-specimen surface with laser-Doppler interferometry and comparing them with calculated displacement distributions. The methodology is applied to lithium niobate (LiNbO 3) and langasite (La 3Ga 5SiO 14) crystals.

Elastic constants, internal friction, and piezoelectric coefficient ofα−TeO2

We studied the interrelationship of elastic and piezoelectric properties with the lattice structure and crystal physics of paratellurite $(\ensuremath{\alpha}\ensuremath{-}{\mathrm{TeO}}_{2}).$ Tetragonal paratellurite ${(D}_{4}^{4},P422)$ shows six independent elastic constants ${C}_{\mathrm{ijkl}},$ the associated internal friction ${Q}_{\mathrm{ijkl}}^{\ensuremath{-}1},$ and one piezoelectric coefficient ${e}_{14}.$ We determined simultaneously these material coefficients using resonant ultrasound spectroscopy coupled with laser-Doppler interferometry. Mode identification, essential for success, was done by measuring the displacement distributions on a vibrating-specimen surface. Our ${C}_{\mathrm{ijkl}}$ were consistent with reported values measured by conventional methods. Our ${e}_{14}$ exceeds the reported value by 53%. We focus on several unusual elastic properties, including a negative Poisson ratio. Considering a star-shape truss structure on the basal plane consistently explains all of them. Internal friction correlates with the ${C}_{\mathrm{ijkl}}$ temperature derivatives, suggesting phonon-phonon interactions as a dominant cause of the mechanical loss.

Elastic, anelastic, piezoelectric coefficients of monocrystal lithium niobate

Using improved acoustic spectroscopy, we determined the complete above coefficients (16 independent ones) by measuring the macroscopic resonance frequencies of a single lithium-niobate monocrystal. The improvement consisted of using laser-Doppler interferometry for unambiguous vibration-mode identification. Elastic coefficients C ijkℓ agree well with previous reports that used conventional methods. Piezoelectric coefficients e ijk agree with the range of four previous reports. Anelastic coefficients Q −1 ijkℓ , reported for the first time, suggest that the crystal's internal friction arises mainly from dislocations, not from intrinsic multiphonon processes.

Elastic constants of chemical-vapor-deposition diamond thin films: resonance ultrasound spectroscopy with laser-Doppler interferometry

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.