Time-Resolved Studies of the Acoustic Vibrational Modes of Metal and Semiconductor Nano-objects

Abstract

Over the past decade, there have been a number of transient absorption studies of the acoustic vibrational modes of metal and semiconductor nanoparticles. This Perspective provides an overview of this work. The way that the frequencies of the observed modes depend on the size and shape of the particles is described, along with their damping. Future research directions are also discussed, especially how these measurements provide information about the way nano-objects interact with their environment.

Tailored Hypersound Generation in Single Plasmonic Nanoantennas

“…Indeed, the generation of hypersonic waves in a variety of materials, geometries and devices, has grown to applications in different areas such as high-frequency electronics [1][2][3], biomedical science [4,5], ultrasensitive mass detection [6,7] and photoacoustic imaging [8,9]. Whereas the generation of coherent vibrations in metal nanoparticles [10][11][12][13], or in small groups of them [14,15] has been subject of active research during the last decade, their applications as local and tunable nanoresonators are still in their beginnings [8].…”

“…initial phase, see also Table 1) with respect to the signal of the naked-rod and center-silica [13,34,35].…”

Acoustic vibrations of metal nano-objects: Time-domain investigations

“…Though the acoustic response of a material is also altered by size reduction down to the nanometric scale [12,[17][18][19][20][21][22][23][24][25][26][27][28][29], this effect has been comparatively less studied, probably because its signature is less straightforwardly observed as compared to that on the optical response. Breaking of the translational invariance in confined systems leads to additional boundary conditions for the acoustic vibrational movement of a nano-object, which translates into the appearance of discrete acoustic modes in its vibrational spectra [12,[17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…Breaking of the translational invariance in confined systems leads to additional boundary conditions for the acoustic vibrational movement of a nano-object, which translates into the appearance of discrete acoustic modes in its vibrational spectra [12,[17][18][19][20][21][22][23][24][25][26][27][28][29]. As a first approximation, these can be interpreted as the bulk material modes with wavelengths satisfying the spatial conditions imposed by confinement (note that because of their weak dispersion, the frequency of the optical phonon modes of semiconductors are only weakly altered [30]).…”

Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire

“…We investigate two types of nanowires with length L > 10 µm and diameter d = 120 and d = 400 nm (Figure 1a). According to the continuum mechanics model that holds at these sizes [27,28], the expected frequencies f of our mechanical nanoresonators are in the range f ∼ c L /d ∼ 10 GHz to 30 GHz. At room temperature, these high frequency acoustic phonons suffer severe attenuation in silicon.…”