BRILLOUIN STUDIES OF SURFACE ACOUSTIC WAVES IN NANOSTRUCTURED PHONONIC CRYSTALS

Abstract

This PhD thesis is devoted to the experimental and simulation studies of surface acoustic waves (SAWs) in one- and two-dimensional (2D) nanostructured phononic crystals (PCs). In particular, the following investigations have been undertaken: (1) SAWs in a 2D chessboard-patterned PC on a SiO2/Si substrate and a 2D antidot-patterned PC with a soft intervening layer were studied. The phononic band structures were mapped by using Brillouin scattering. Numerical simulations, based on the finite element analysis, revealed unusual surface optical-like modes, which exhibit out-of-phase vibrational characteristics between neighboring elements. In the antidot-patterned PC, an acoustically isolating feature arising from the additional soft layer has also been observed and accounted for. (2) Defect-induced SAWs were studied in a 1D PC, where the periodic defects are stripes with non-regular widths. Nearly dispersionless defect branches, which exhibit localization features and are frequency-tunable by varying the defect stripe size, were observed within the bandgap.