Nondestructive Measurements of the Mechanical and Structural Properties of Nanostructured Metalattices

Abstract

Metalattices are artificial 3D solids, periodic on sub-100 nm length scales, that enable the functional properties of materials to be tuned. However, because of their complex structure, predicting and characterizing their properties is challenging. Here we demonstrate the first nondestructive measurements of the mechanical and structural properties of metalattices with feature sizes down to 14 nm. By monitoring the time-dependent diffraction of short wavelength light from laser-excited acoustic waves in the metalattices, we extract their acoustic dispersion, Young’s modulus, filling fraction, and thicknesses. Our measurements are in excellent agreement with macroscopic predictions and potentially destructive techniques such as nanoindentation and scanning electron microscopy, with increased accuracy over larger areas. This is interesting because the transport properties of these metalattices do not obey bulk predictions. Finally, this approach is the only way to validate the filling fraction of metalattices over macroscopic areas. These combined capabilities can enable accurate synthesis of nanoenhanced 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].…”

Fabricating and Assembling Acoustic Metamaterials and Phononic Crystals

“…In recent years, surface PCs have also played a major role in advanced nanometrology research for reliable characterization, mass-sensing applications, and nondestructive testing of nanosystems. [133][134][135] Schemes involving the optoacoustic excitation of surface PCs offer unprecedented sensitivity for detecting even picometer-range displacements, using technologies such as extreme ultraviolet (EUV) tabletop laser sources. [71] Apart from being able to fabricate complex AMM and PC designs, microfabrication can provide the means for active control and tunability.…”