Investigation of gold/GaN nanorod arrays for hypersonic detection: The effect of periodicity

Gold nanodisk arrays on the upper surface of GaN nanorods were developed with the aim of achieving hypersonic imaging with a detection frequency above 10 GHz. In this paper, we report the interesting phenomenon that the hypersonic signal detected by a single gold nanodisk in this structure might be dependent on the array periodicity and rod length. When the array periodicity is of the same order of or longer than the surface hypersonic wavelength, the detected signal would be enhanced by the period-dependent resonance of the surface hypersonic waves scattered by the nanorod/substrate interface. When the array periodicity is smaller than the surface hypersonic wavelength, the coupling of extensional modes between neighboring nanorods, as the detection frequency approaches the coupled-extensional-mode frequency, would enhance the detected signals. Although these enhancements are beneficial to heat transport at nanorod/substrate interfaces, they will cause cross-talk between the neighboring detection rod uni...