23 research outputs found
Coupled oscillators model for hybridized optical phonon modes in contacting nanosized particles and quantum dot molecules
Modification of optical phonon spectra in contacting nanoparticles as
compared to the single ones is studied. Optical phonons in dielectric and
semiconducting particles obey the Euclidean metric Klein-Fock-Gordon equation
with Dirichlet boundary conditions. The latter is supposed to be solved
numerically for manifolds of interpenetrating spheres. It is proposed to
replace this problem with the simpler-to-solve coupled oscillators model (COM),
where an oscillator is attributed to each phonon mode of a particle and the
particles overlap leads to appearance of additional couplings for these
oscillators with the magnitude proportional to the overlapped volume. For not
too big overlaps this model describes solutions of the original eigenvalue
problem on a good level of accuracy. In particular, it works beyond isotropic s
modes, which has been demonstrated for p modes in dimer and also for tetramer.
It is proposed to apply COM for the description of recently manufactured dimer
nanoparticles and quantum dots. The obtained results are in agreement with the
dynamical matrix method for optical phonons in nanodiamonds. The latter is used
to demonstrate that the van der Waals contacts between faceted particles lead
to very small modifications of the optical phonon spectra, which therefore
could be neglected when discussing the propagation of vibrational excitations
via a nanopowder. The possibility to distinguish between dimerized and
size-distributed single particles from their Raman spectra is also considered.Comment: 11 pages, 10 figure
Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: escape from phonon confinement
In the present paper, we utilize the coupled-oscillator model describing the
hybridization of optical phonons in touching and/or overlapping particles in
order to study the Raman spectra of nanoparticles organized into various types
of regular and random arrays including nanosolids, porous media, and
agglomerates with tightly bonded particles. For the nanocrystal solids, we
demonstrate that the ratio of the size variance to the coupling strength allows
us to judge the character (localized or propagating) of the optical phonon
modes which left the particles of their origin and spread throughout an array.
The relation between the shift and the broadening of the Raman peak and the
coupling strength and the disorder is established for nanocrystal solids,
agglomerates, and porous media providing us with information about the array
structure, the structure of its constituents, and the properties of optical
phonons.Comment: 13 pages, 11 figure
Raman Spectra of Crystalline Nanoparticles: Replacement for the Phonon Confinement Model
International audienc