Fabrication and physical properties of self-organized silver nanocrystals

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.