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

Abstract

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.

Towards acoustic microscopy at the nanoscale by coupling atomic force microscopy with picosecond ultrasonics

“…Since picosecond acoustics was developed by Thomsen et al [1,2], time-resolved pump-probe spectroscopy has proven to be a very effective way to probe and image nanoscale elastic properties of a wide variety of materials. Employed both, in industrial and fundamental research, it has recently been used to perform elasticity imaging of various systems such as biological cells [3][4][5][6][7][8][9][10] and polycristalline materials [11][12][13]. The generation of acoustic waves with frequencies up to a couple hundred GHz enables achievement of very good in-depth resolution [14].…”

Analytical model of the acoustic response of nanogranular films adhering on a substrate

“…In this context photoacoustic nanometrology plays a key role. For instance, the bulk properties of periodic nanogranular thin films have been explored across a variety of configurations [13,14] ranging from 1D [15], 2D [16][17][18][19][20][21][22] to 3D [23,24] arrangements. Recently, the development of table-top UV laser sources allowed generating surface acoustic waves with periodicity in the 10 nm range [25], hence opening to mechanical nanometrology [26] of periodic granular thin films of thicknesses down to few nanometers [27,28].…”