“…The excitation of a longitudinal wave in the GHz range has been reported by Hadimioglu et al using a 0.4-mm-thick (0001) textured polycrystalline ZnO film. 4) Such piezoelectric thin films have been widely used in signal processing devices, 5,6) sensors, 7,8) and ultrasonic spectroscopy such as acoustic microscopy 9,10) and piezoelectrically induced phonons for Brillouin scattering measurements. 11,12) In contrast, it is difficult to excite shear waves in the GHz range.…”