Nanocontact Tailoring via Microlensing Enables Giant Postfabrication Mesoscopic Tuning in a Self-Assembled Ultrasonic Metamaterial

The ability to tune the resonant frequency of a self-assembled ultrasonic metamaterial with mesoscale spatial resolution, after fabrication, by up to 250% is demonstrated. This tunability is achieved by the microlensing-enabled modification of nanocontact features, wherein the metamaterial resonant elements dig in to the substrate. In addition to tunability exceeding prior MHz-GHz frequency ultrasonic metamaterial examples, the system presented herein can be tuned after assembly at a spatial resolution commensurate with the laser spot's diameter. It is posited that these aforementioned advantages will enable a new class of ultrasonic gradient index devices, such as ultrasonic elastic wave cloaks, that can be manufactured in a scalable manner and then rapidly tuned. Finally, it is expected that this large tunability at ultrasonic frequencies will have broader application to areas including optomechanics, acoustoplasmonics, quantum-mechanical oscillators, and adhesion control.