Acoustic microscopy measurement of elastic constants by using an optimization method on measured and calculated SAW velocities : effect of initial Cij values on the calculation convergence and influence of the LFI transducer parameters on the determination of the SAW velocity
Résumé
The determination of elastic constants in anisotropic solids by line-focus acoustic microscopy (LFAM) is discussed. The velocity of leaky surface acoustic waves (SAWs) has been obtained for different directions of propagation (φ) from the V(z) curves. The elastic constants are determined from the comparison of measured and calculated velocities. The principle is based on the minimization of the summation of the square difference ∑|VΦc−VΦm|2, by using a Simplex method. This paper deals with the case of cubic-crystallite solids defined by three independent elastic constants. The influence of the initial values of cij on the final result is discussed in the case of MgO substrate and TiN deposited on MgO substrate. Experimental SAW velocity profile is measured on (100) silicon substrate as a function of φ between [100] and [010] directions. The influence of the transducer parameters and defocusing distance are also discussed.