Fabrication and physical properties of self-organized silver nanocrystals
M. P. Pileni
Laboratoire SRSI, URACNRS 1662, Université P.
et M. Curie (Paris VI), B.P. 52, 4 Place Jussieu, F - 752 31 Paris Cedex
Abstract: A simple method is used to prepare highly monodispersed
silver nanoparticles in the liquid phase, which starts from an initial
synthesis in functionalized AOT reverse micelles. To narrow the particle
size distribution from 43 to 12.5% in dispersion, the particles are
extracted from the micellar solution. The size-selected precipitation
method is used. The nanocrystallites dispersed in hexane are deposited
on a support. A monolayer made of nanoparticles with spontaneous compact
hexagonal organization is observed. The immersion of the support on
the solution yields to the formation of organized multilayers arranged
as microcrystal in a face-centered-cubic structure.
We compare the optical properties of spherical particles organized
in a two- and three-dimensional structure with isolated and disordered
particles. When particles, deposited on cleaved graphite, are arranged
in a hexagonal array, the optical measurements under p-polarization
show a new high-energy resonance, which is interpreted as a collective
effect, resulting from optical anisotropy due to the mutual interactions
between particles. We support this interpretation by numerical calculations
performed for finite-size clusters of silver spheres. For disordered
particles, a low-energy resonance appears instead of the high-energy
resonance observed for spherical and organized particles. This is interpreted
as optical shape anisotropy due to the asymmetrical arrangement of particles.
The tip of a scanning tunneling microscope (STM) may be used as an
extremely localized source of low-energy electrons to locally excite
photon emission from a variety of metal films. The detection of locally
excited luminescence at the junction of an STM tip provides access to
electron dynamic properties at the surface, which makes it possible
to study luminescence phenomena of nanometer-sized structures.
The photon intensity emitted from electrically isolated silver nanoparticles
self-organized as a 2D network on a gold (111) substrate is analyzed.
We observed unexpectedly strong variations of photon-emission efficiency
from isolated nanoparticles, depending on how tightly they are embedded
within the network site. The quenching site observed in the STM photon
emission map is interpreted as an enhanced interaction of electrons
with surface photon modes.
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