Morphology-Dependent Coherent Acoustic Phonon Vibrations and Phonon Beat of Au Nanopolyhedrons

Abstract

Coherent acoustic phonon vibrations of Au nanopolyhedrons, including nanocubes, nano-octahedrons, and nanocuboctahedrons, in aqueous solutions and poly(vinyl alcohol) (PVA) films, were investigated using transient absorption (TA) spectroscopy combined with finite element analysis based on continuum elastic theory. In each type of nanopolyhedron, two vibrational modes with similar quality factors (Qs) and phases were observed, suggesting that both were induced by thermal expansion. The low-frequency vibrational mode represents a tipto-tip displacement in each nanopolyhedron, whereas the high-frequency mode is the breathing vibration of the whole particle and reveals morphology dependence, displaying a face-to-face displacement in nanocuboctahedrons, an edge-to-edge displacement in nano-octahedrons, and a combination of face-to-face and edge-toedge displacements in nanocubes. Moreover, a clear phonon beat was identified in the two vibrational modes of the nanocuboctahedrons. Our experimental results provide a possible application of morphology-controllable metal nanoresonators.

Nickel Slag/Laterite Soil and Nickel Slag/Iron Sand Nanocomposites: Structural, Optical, and Electromagnetic Absorption Properties

“…The wider Δ­(LO – TO) indicates the stable bonding of the nanocomposite, and the higher value of NS indicates that the bonding is more stable than others. This finding can be attributed to the differences in bond stability because of the effects of doping and the formation of new bonds; thus, the addition of IS and LS successfully reconditions the initial state of the fayalite structure in NS and can stimulate coherent vibrations …”

“…This finding can be attributed to the differences in bond stability because of the effects of doping and the formation of new bonds; thus, the addition of IS and LS successfully reconditions the initial state of the fayalite structure in NS and can stimulate coherent vibrations. 57 In Figure 4 (fourth row), the NS/IS nanocomposite exhibits the highest wavenumber position change of α, which can be attributed to the structural properties and more compact bonds. 58−60 Furthermore, the highest wavenumber position for the attenuation and phase constants of NS/IS corresponds to the amount of magnetite and the atomic density of IS.…”

Acoustic Vibration Modes of Gold–Silver Core–Shell Nanoparticles

“…This contrasts with the literature where only two modes, extensional and breathing, were reported for bimetallic core-shell NPs with a AuNR core and a thinner Ag [19,24] or Pd [25] shell. First, NPs with a thin shell coating have a rod-like shape, whereas the AuNR@Ag samples considered here (with a thicker Ag coating) have cuboid (orthogonal parallelepiped) shapes (see Section 2.1) whose vertices and edges also contribute to the appearance of additional vibration modes [17,39,40]. This can be seen from the mode shapes, in Figure 4e-h, of the AuNR@Ag 2eq sample having sharp edges and corners.…”

“…On the contrary, we observe a pronounced enhancement in the modes that are dominated by the vertex oscillations, namely, mode 2 and the minor modes that appear between modes 1 and 2 (see the arrow in Figure 5a and Figure S5 in the Supplementary Materials). This could be taken as an indicator for a progressive transformation of the cuboid NPs into cubic NPs, in which the vertex oscillation contribution plays a large part, if the Ag overgrowth is continued further [17,40]. Let us now discuss about the vibration mode shift.…”

“…Among all NPs, single-metal spheres are the easiest to synthesize and model in terms of mechanical properties and, as a result, were studied early on [5][6][7][8]. Since then, other shapes have been investigated, such as ellipsoids [9], rods [10][11][12], bipyramids [13,14], rings [15], disks [16] and polyhedra [17]. Other studies [13,[18][19][20] reviewed the origins of damping (internal or due to a liquid medium or to a substrate).…”