Impulsively excited Surface Phononic Crystals: A route towards novel sensing schemes

Abstract

The application of all-optical time resolved techniques to nanostructured Surface Phononic Crystals enables the generation and detection of hypersonic frequency surface acoustic waves up to 50 GHz, with great potential for breakthroughs in nanometrology and sensing applications. Here we review the advances in this field both in the theory and experiments, focusing on the progress in non-destructive ultrathin films nanometrology and the promise of dramatically increasing mass sensors sensitivity due to enhanced acoustic wave surface confinement.

Mechanical Properties of Ag Nanoparticle Thin Films Synthesized by Supersonic Cluster Beam Deposition

“…In the ASOPS system, the pump−probe time delay is managed electronically, avoiding any moving mechanical parts. 18 This fact, together with a laser repetition rate of 100 MHz, allows detection of relative transmission (reflectivity) changes in the 10 −7 range. For these reasons ASOPS is arising as the go-to photoacoustic technique for the investigation of the mechanical properties of nanoscale materials.…”

Mechanical Properties of Nanoporous Metallic Ultrathin Films: A Paradigmatic Case

“…We pinpoint that a typical displacement involved in picosecond photoacoustic experiments is in the range of 1 to 10 pm (depending on the exploited pump pulse energy) for thicknesses in the order of 10 nm, thus resulting in a strain in the order of 10 −3 -10 −4 . Hence, in its various forms, photoacoustic nanometrology is emerging as the go-to technique for the inspection of thin-film [39,[49][50][51][52][53][54], ultrathin film [37,[39][40][41][42][43], and nanoparticle [55,56] mechanics, and the topic is in rapid and continuous evolution. Cross-feed from other topical areas has recently resulted in novel inspection protocols based on the photoacoustic effects.…”

“…Cross-feed from other topical areas has recently resulted in novel inspection protocols based on the photoacoustic effects. For instance, advances in table-top UV laser technologies, coupled to state-of-the-art electron beam lithography, opened the way to the mechanics of thin films of thickness down to few nanometers [25,39,43]. An alternative route to measure the mechanical properties of thin films is the picosecond photoacoustic method, a non-invasive optical technique that relies on the excitation of the system's mechanical breathing modes and their detection via the acousto-optic effect [37][38][39][40][41][42][43][44][45][46][47][48].…”

“…For instance, advances in table-top UV laser technologies, coupled to state-of-the-art electron beam lithography, opened the way to the mechanics of thin films of thickness down to few nanometers [25,39,43]. An alternative route to measure the mechanical properties of thin films is the picosecond photoacoustic method, a non-invasive optical technique that relies on the excitation of the system's mechanical breathing modes and their detection via the acousto-optic effect [37][38][39][40][41][42][43][44][45][46][47][48]. In brief, the energy delivered by a femtosecond laser pump pulse heats the film, triggering an impulsive thermal expansion.…”

“…Cross-feed from other topical areas has recently resulted in novel inspection protocols based on the photoacoustic effects. For instance, advances in table-top UV laser technologies, coupled to state-of-the-art electron beam lithography, opened the way to the mechanics of thin films of thickness down to few nanometers [25,39,43].…”