Selectively probing vibrations in a plasmonic supracrystal

Abstract

The coupling of plasmonic resonances with the multiple phonon modes of a plasmonic supracrystal is studied. Ultrafast optical pump-probe spectroscopy with variable wavelength allows the selective detection of the breathing mode, the interparticle vibrations, and the vibration of the whole structure. Thanks to this selectivity, the characterization of the bonding strength between nanoparticles in different directions of the supracrystal is possible. The observation of these vibrations could be useful for the realization of future phonon modulated photonic and plasmonic devices.

Ultrafast acousto-plasmonics in gold nanoparticle superlattices

“…Because laser-excited hot electrons are confined in the gold nanoparticles, these observations indicate that the acoustic phonons are very likely induced by ultrafast heating of the superlattice assisted by a collective plasmon-polariton propagation. While individual vibrations of nanoparticles assemblies have been reported earlier [20,21] or narrowband Brillouin mode in semitransparent cobalt superlattice [22], our results demonstrate that it is possible to generate propagating broadband coherent acoustic phonons in plasmonic NPS.…”

“…Because laser-excited hot electrons are confined in the gold nanoparticles, these observations indicate that the acoustic phonons are very likely induced by ultrafast heating of the superlattice assisted by a collective plasmon-polariton propagation. While individual vibrations of nanoparticles assemblies have been reported earlier [20,21] …”

“…Following the hcp lattice dynamic equation along the z axis, we can connect the sound velocity to the nanoparticle contact effective stiffness K with V LA =(4/ √ 3)d K/m [32] where d=5.1 nm is the interparticle distance. With a particle diameter of 3.7 nm the mass becomes m=5.1.10 −22 kg, leading to K ≈ 11 N.m −1 consistently with covalent bonds and larger than Van der Waals connection probed in soft assemblies of nanoparticles [21,30].…”

Interrogating Nanojunctions Using Ultraconfined Acoustoplasmonic Coupling

“…The contact area has previously been estimated via acoustooptics for films containing many millions of particles, and therefore, many millions of contacts. This removes any effect due to individual contacts and employs spherical approximations that are inadequate for describing single nanocontact dynamics [13,14]. Acoustoplasmonic spectroscopy can thus become a valuable tool for structural and mechanical analysis at the nanoscale.…”

Studying periodic nanostructures by probing the in-sample optical far-field using coherent phonons

“…Thus, the interaction of the vibrational phonon modes and light was studied experimentally by picosecond acoustic techniques in periodic structures which possess both photonic and phononic band gaps (i.e., photonic-phononic crystals), 9,10 hole arrays, 11 metallic gratings, [12][13][14] and complex periodic plasmonic nanostructures. 15 Less attention was paid to the elasto-optical effects that occur in bulk solid media at a distance from the nanostructure larger than the optical wavelength, where light has a well-defined wavevector and a corresponding propagation direction. 16 The spatial and spectral distributions of this far-field region are changed due to the diffraction of light by a periodic nanostructure.…”