EFFICIENT EXCITATION AND DETECTION OF GUIDED ACOUSTIC WAVES IN SEMICONDUCTOR NANORODS THROUGH EXTERNAL METALLIC ACOUSTIC TRANSDUCER
Szu-Chi Yang1*, Yueh-Chun Wu1, Pierre-Adrien Mante1, Chien-Cheng Chen1, Hung-Pin Chen1, Hsiang-Yu Chou2, Min-Hsiung Shih2, Chi-Kuang Sun1,2,3
1Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
2Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
3Molecular Imaging Center and Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan
* presenting author:楊思齊, email:jk76119@hotmail.com

In this study, we report that guided acoustic waves (GAWs) can be excited in nanorods through an external metallic acoustic transducer realized by directly depositing gold nanodisks on top of GaAs nanorods. During the top-down fabrication process of the GaAs nanorods, the gold nanolayer was deposited before the etching process so that both the diameter and the period of the gold nanodisks could perfectly match those of the rods. Through optical excitation with a femtosecond laser and coupling of the lateral vibrational modes of the gold nanodisks into the nanorods, the external acoustic transducer enables the generation of GAWs in the nanorods. Furthermore by choosing the resonant wavelength of localized surface plasmons (LSPs), we are able to excite LSPs at the interface between gold and GaAs. The acoustic detection sensitivity is thus greatly enhanced. In the experiment, the propagation behavior of the observed GAWs is analyzed, which indicates a strong reduction of the GAWs group velocity resulting from the nano-confinement is observed, when compared to the bulk. Meanwhile, the similar mode shape between the lateral vibrational mode of gold nanodisk and excited GAWs in the nanorod leads the observation of high coupling efficiency of our external acoustic transducer in the experiment. These results may not only lead to the development of efficient external transducers for acoustic imaging, but also provide an experimental system for studying acoustic phonon transport behavior in nanorods and nanowires.


Keywords: Nanorod, Nanodisk, Guided Acoustic Waves, Localized Surface Plasmons, Femtosecond Pump-Probe Technique