Probing confined acoustic phonons in free standing small gold nanoparticles

Abstract

Polarized and depolarized spectra from gold (Au) nanoparticles of different sizes are investigated in the small size range, between 3 and 7 nm, using low frequency Raman spectroscopy. Acoustic vibrations of the free-standing Au nanoparticles are demonstrated with frequencies ranging from 5 to 35 cm−1, opening the way to the development of the acoustic resonators. A blue shift in the phonon peaks along with the broadening is observed with a decrease in particle size. Comparison of the measured frequencies with vibrational dynamics calculation and an examination as from the transmission electron microscopy results ascertain that the low frequency phonon modes are due to acoustic phonon quantization. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar (l = 2) vibrations of the spheroidal mode due to plasmon mediated acoustic vibrations in Au nanoparticles.

Dielectric function of two-phase colloid–polymer nanocomposite

“…for the use in highly sensitive sensors on a single molecule level. [24][25][26][27] The optical properties of a single nano-sphere, including the LSP resonance, can be calculated analytically by Gustav Mie's theory for spherical colloids. 43,45 Predicting the properties of nanocomposites is more difficult, as both the dielectric functions of the matrix, e m , and of the inclusions, e inc , as well as the distribution of particles have to be taken into account.…”

“…In particular the sensitivity of the LSP to the dielectric properties of the environment is highly relevant for applications, like the fabrication of extremely precise sensors. [24][25][26][27] based on the electrostatic interaction of polyelectrolyte polymers. 12 Unlike conventional nanocomposites these LbL-films are highly homogenous and allow a very precise control of the layerthickness.…”

Radial vibration of ultra-small nanoparticles with surface effects

“…In the previous studies, the inverse relation is often regarded as the size-dependence of nanoparticles [6][7][8][9]. However, there are no any microscopic factors in Lamb theory, and the inverse relation does not reflect the particular size-dependence in nanoscale.…”

“…Multitudinous artificial and natural nanoparticles have spherical or quasi-spherical shapes, thus most discussions on the mechanics just treat them as nanospheres. Early in 1881, Lamb [5] calculated the vibrational modes of an elastic sphere and provided the eigenfrequencies of the free boundary condition, which has been often used as the theoretical basis of nanoparticles' vibration testing such as low frequency Raman scatting [6][7][8] and pump-probe tests [9] etc. However, lots of recent studies show that the prediction by Lamb maybe fail for ultra-small nanoparticles who are smaller than 3nm of radii and only have serval(or a little more) atomic layers in radial direction [10].…”

Formation of cyanide compounds during preparation of gold surfaces evidenced by surface‐enhanced Raman spectroscopy

“…Bulk gold has no Raman signal, and the unidentified modes cannot be associated with the vibrational signature of this metal. In the particular case of gold nanoparticles, acoustic modes can be observed at very low wavenumber (typically 35 cm −1 for nanoparticles of 3.2 nm diameter, and the wavenumber downshifts if the diameter increases) . This suggests that these modes are coming from a molecule present at the surface of the metal.…”