Surface Acoustic Wave Spectroscopy Research Articles

Thin-Film Aerogel Porosity and Stiffness Characterized by Surface Acoustic Wave Spectroscopy

ABSTRACTDensity/porosity and stiffness are the most critical parameters determining properties of porous films, however they are difficult to measure. Here we report characterization of density/porosity and Young's modulus values of a range of nanoporous silica aerogel films via dispersion of laser-generated wideband surface acoustic waves. Results are compared to dielectric constant, Rutherford Backscattering Spectrometry (RBS), Ellipsometric Porosimetry (EP) and Nanoindentation (NI). RBS density correlates well to SAW. EP and NI also show a correlation, however the absolute values do not match. Low Young's modulus values show that the film stiffness is drastically reduced with increasing porosity. The technique is rapid, nondestructive and relatively inexpensive, and yields absolute values of nanoporous aerogel elastic properties which are useful for process control and are difficult to access with other techniques.

K-0633 複合コーティング膜の弾性率におよぼす硬質または軟質粒子の分散効果(S06-1 膜質の応力解析とキャラクタリゼーション)(S06 コーティング材の力学特性と損傷機構)

Elastic constants of several kinds of Ni-P composite coatings are determined using a surface acoustic wave spectroscopy, and the ultrasonically determined Young's moduli are compared with mechanically determined ones using a nanoindentation in order to examine the validity of the measured values. The experimental results have shown that the Young's moduli determined ultrasonically and mechanically almost agree with each other. The results have also clearly shown that increasing SiC particles content causes an increase in Young's modulus of the composite coating and the Young's modulus is decreased by increasing Teflon particles content. These results are in agreement with the theoretically estimated ones. Thus, the dispersion effect of hard or soft inclusions to the elastic property of composite coating has been shown quantitatively.

Photoinduced Chemical Vapor Deposition of Amorphous Carbon Films from Chloromethane Using a VUV Laser (157 nm)

Amorphous carbon (a-C) films with low hydrogen content were deposited at low substrate temperatures from a chlorinated hydrocarbon (CH3Cl) by photoinduced chemical vapor deposition with a fluorine laser (157 nm). The optical gap, as determined by photothermal deflection spectroscopy (PDS), decreased from 2.3 to 0.1 eV when the substrate temperature was increased from 303 to 643 K. The films were further characterized by FTIR spectroscopy, micro-Raman spectroscopy, surface acoustic wave spectroscopy (SAWS), and atomic force microscopy (AFM). The presence of chlorine residues in the films was examined by energy-dispersive X-ray fluorescence (EDXRF) spectroscopy. The amount of chlorine decreased significantly between 493 and 518 K, causing the carbon network to restructure into a more graphitic form. Deposition at 643 K produced a chlorine-free a-C film on the quartz substrate.

Density and elastic constants of hot-filament-deposited polycrystalline diamond films: methane concentration dependence

Polycrystalline diamond films with a thickness of about 4 μm were deposited with the hot-filament technique using methane concentrations between 0.5 and 2.0% in the source gas. Surface acoustic wave spectroscopy (SAWS) was employed to determine the density. Young's modulus (elastic or E modulus), and Poisson's ratio from the dispersion of propagating surface wave pulses. With decreasing CH4 concentration in the deposition gas, the density increased from 3.4 g cm★ to 3.5 g cm★ while the Young's modulus increased from 925 GPa to 1080 GPa, showing the improved mechanical and elastic properties for low methane concentrations. These results are correlated to those of other characterization methods such as Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Density and Young’s modulus of thin TiO 2 films

Densities, ρ, of thin TiO2 layers, produced by reactive evaporation (RE) and ion plating (IP) have been analyzed by means of grazing incidence X-ray reflectometry (GIXR). Depending on the deposition conditions, the layers are amorphous or polycrystalline, with densities between 2.9 g/cm3 and 3.9 g/cm3. Young’s moduli, E, have been analyzed for 280 nm and 500 nm thick layers by means of surface acoustic wave spectroscopy (SAWS) and vary between 65 GPa for RE films and 147 GPa for IP layers. The values are independent of film thickness, but correlate with the density. A phase transition of the TiO2 films from the amorphous state to anatase occurs at temperatures above 210°C and increases the Young’s modulus significantly, whereas the density remains unchanged.

Young's Modulus and Density of thin TiO2 Films Produced by Different Methods

AbstractThe Young's modulus and density are analyzed for 280 and 500 nm thick TiO2 layers deposited by reactive evaporation (RE) and ion plating (IP) by means of surface acoustic wave spectroscopy (SAWS) and grazing incidence X-ray reflection spectroscopy (GIXR). The layers are amorphous or polycrystalline, and have densities between 2.9 g/cm3 and 3.8 g/cm3, depending on the deposition conditions. The measured Young's moduli vary between 65 GPa for RE films and 147 GPa for IP layers. They are independent of film thickness, but correlate with the density. A change of the Young's modulus due to the phase transition from amorphous to anatase is described, which occurs at temperatures above 210°C.

Mechanical and elastic properties of amorphous hydrogenated silicon films studied by broadband surface acoustic wave spectroscopy

Mechanical and elastic properties of a-Si∶H films were measured by broadband Surface Acoustic Wave Spectroscopy (SAWS). In the frequency range achieved, the SAW dispersion curves extend to 300 MHz, which allowed the density, Young's modulus, and Poisson's ratio to be evaluated for films grown by laser CVD or plasma CVD with different hydrogen concentrations. The films deposited by either method have the best mechanical and elastic properties. at a hydrogen concentration of about 10 at. %. For this material, a density of (2300±20) kg/m3 and Young's modulus of (134±5) GPa was determined. The network structures of amorphous silicon are discussed by applying the constraint-counting model to estimate the mean coordination number.

Mechanical and elastic properties of amorphous hydrogenated silicon films studied by broadband surface acoustic wave spectroscopy

Mechanical and elastic properties of amorphous hydrogenated silicon films studied by broadband surface acoustic wave spectroscopy

Laser diagnostics of C 60 and C 70 films by broadband surface acoustic wave spectroscopy

A novel method is used for the determination of mechanical and elastic properties of thin films such as film thickness, density, Young's modulus, and Poisson's ratio. In this technique short laser pulses (nanosecond to picosecond) are used to excite a surface acoustic wave (SAW) pulse and laser probe beam deflection or a piezoelectric foil detector are employed for time-resolved detection of the resulting surface displacements. Fourier transformation of the oscillatory signals detected at distances of several millimeters to centimeters yields the dispersion of the phase velocity, which can be used for the accurate determination of film properties. Fullerite films (C 60 and C 70) with thicknesses of 0.7–2.1 μm on silicon and quartz-glass substrates were investigated. The nonlinear dispersion curves were obtained experimentally with a maximum value of the product of film thickness and SAW wave number of γ max = 0.32 for the C 60 films and γ max = 0.18 for the C 70 films. The frequency bandwidth was limited by the attenuation of the surface acoustic waves in the fullerite films. The film parameters were evaluated by fitting the measured dispersion curve to a theoretical model. For the C 60 films a density of 1.67 ± 0.02 g/cm 3, Young's modulus of 10 ± 2 GPa, and Poisson's ratio of 0.25 ± 0.08 were found. For the C 70 films the corresponding values were 1.64 ± 0.02 g/cm 3, 4 ± 1 GPa, and 0.35 ± 0.1.

Study of Mechanical and Elastic Properties of Diamond Films by Surface Acoustic Wave Spectroscopy (SAWS)

ABSTRACTThe density and elastic properties of a 1.9 μm thick polycrystalline diamond film deposited on a silicon substrate were measured by surface acoustic wave (SAW) spectroscopy. A density of 3.45±0.05 g/cm3, Young's modulus of 940 ± 20 GPa and Poisson's ratio below 0.12 were determined from the dispersion of a broadband coherent surface acoustic wave pulse propagating in the layered system. The surface wave pulses were generated using a ns UV laser pulse and detected with a piezoelectric foil transducer.