Jacob, Philip; Alex,A V(Indian Academy of Sciences, January , 2004)
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Abstract:
Certain organic crystals are found to possess high non- linear optical coefficients,often one to two orders of magnitude higher than those of the well known inorganic non-linear optical materials.Benzoyl glycine is one such crystal whose optical second-harmonic generation efficiency is much higher than that of potassium dihydrogen phosphate. Single crystals of benzoyl glycine are grown by solvent evaporation technique using N,N-dimethyl formamide as the solvent.All the nine second-order elastic stiffness constants of this orthorhombic crystal are determined from ultrasonic wave velocity measurements employing the pulse echo overlap technique.The anisotropy of elastic wave propagation in this crystal is demonstrated by plotting the phase velocity, slowness,Young's modulus and linear compressibility surfaces along symmetry planes.The volume compressibility, bulk modulus and relevant Poisson's ratios are also determined. Variation of the diagonal elastic stiffness constants with temperature over a limited range are measured and reported.
Jacob, Philip; Khan, A; Hess, P(American Institute of Physics, February 15, 2004)
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Abstract:
The Young’s modulus and Poisson’s ratio of high-quality silicon nitride films with 800 nm thickness,
grown on silicon substrates by low-pressure chemical vapor deposition, were determined by
measuring the dispersion of laser-induced surface acoustic waves. The Young’s modulus was also
measured by mechanical tuning of commercially available silicon nitride cantilevers, manufactured
from the same material, using the tapping mode of a scanning force microscope. For this
experiment, an expression for the oscillation frequencies of two-media beam systems is derived.
Both methods yield a Young’s modulus of 280–290 GPa for amorphous silicon nitride, which is
substantially higher than previously reported (E5146 GPa). For Poisson’s ratio, a value of n
50.20 was obtained. These values are relevant for the determination of the spring constant of the
cantilever and the effective tip–sample stiffness