ACOUSTIC-PHONON MODES OF FREESTANDING RECTANGULAR WIRES

We theoretically investigate acoustic phonon modes of free-standing sq uare and rectangular wires of cubic crystals, using a resonant ultraso nic method. The normal modes consist of a compressional made termed th e dilatational mode and non-compressional modes referred to as torsion al, shear and flexural modes. The dispersion relations of the dilatati onal mode are obtained for square and rectangular GaAs wires, taking a ccount of elastic anisotropy of the material, showing non-linear dispe rsion relations with subband structure. The change of the dispersion r elations due to the difference in the cross-sectional shape is investi gated. We also examine the displacement of these modes and show the ex istence of acoustic edge modes. (C) 1997 Academic Press Limited.