Michaela Janovská

Anisotropic elasticity of DyScO3 substrates

The full elastic tensor of orthorhombic dysprosium scandate (DyScO(3)) at room temperature was determined by resonant ultrasound spectroscopy (RUS). Measurements were performed on three 500 μm thick substrates with orientations (110), (100) and (001) in the Pbnm (a < b < c) setting. For this purpose, a modification of the RUS method was developed, enabling simultaneous processing of the resonant spectra of several platelet-shaped samples with different crystallographic orientations. The obtained results are compared with ab initio calculations and with elastic constants of other rare-earth scandates, and are used for discussion of the in-plane elasticity of the (110)-oriented substrate.

Elastic constants of nanoporous III-V semiconductors

Resonant ultrasound spectroscopy is applied to determine elastic constants of nanoporous gallium arsenide and indium phosphide single crystals with various pore morphologies. Three samples with approximately the same level of porosity (30%) are studied; it is shown that in all cases this porosity leads to a decrease of Youngs moduli by more than 50% and to a significant increase of the Poissons ratios, while the strength of the resulting elastic anisotropy of the nanoporous material follows from the particular morphology of the pores. The experimentally obtained elastic constants are compared to those predicted for the given morphologies by finite elements modeling. It is observed that the numerical models give acceptably realistic predictions of the elastic constants, although they tend to underestimate the decrease of the elastic moduli due to the porosity as well as the corresponding increase of the Poissons ratio.