Construction of nanoscale devices is a crucial step toward the sucess of nanotechnologies in a variety of fields. Although construction by addition of individual building blocks might appear impossible without using nanomachines, it can actually be carried out by simply exploiting the different magnitude of attractive and repulsive interaction forces at the nanoscale. For example, gravity is negligible for nanoparticles, but other forces become dominant and require the nanoparticles to be coated with selected molecules. Thus, one can simply let the solvent evaporate and wait the nanoparticles to organize into ordered structures without any intervention. Such strategy is one of the core of the concept of self-assembly.
Gold and silver nanoparticles
Plasmonic nanoparticles (Au and Ag) have been object of fascination since ancient time for the preparation of stained glass. Such elementary building block are extremly robust and their use in monuments stand the test of time. A not too far example from the laboratory is the "Sainte-Chapelle du Palais" at "l'île de la cité" in Paris (see image, wikipédia). This phenomenon, commonly witnessed by everyone, originates from the electromagnetic properties of metallic nanoparticles.
Optical properties of nanoparticles
The strong optical properties of the nanoparticles can be tuned across the visible to the mid infra-red range by modifying their size and shape. When such nanoparticles are organized in ensembles, collective properties are obtained that differ from those of individual particles and the resulting optical properties can be further tuned and even amplified. In particular, plasmon coupling in small gaps (1–10 nm) between plasmonic nanoparticles results in intense electric fields (i.e.,hot-spots) that can be exploited for many purposes, such as sensing, biomaterials, metamaterials design, switching devices, and so forth.
Use of light to study nanoparticles self assembly
We use UV/Vis spectrometry and X-ray scattering tecniques (SAXS) to study nanoparticles super-structures. The structural study of the material is the first step before understanding its overall properties and considering applications. SAXS is an experimental technique used to study the structural properties of materials and gives information on the size and orientation of the nanoparticles, their arrangement, the characteristic interdistances and the possible long-range organization. In a scattering experiment, ordered phases give diffraction signals that are called Bragg peaks. Analysis of such signals requires adapting standard methods of crystallography to the nanoscale, as the relevant length scale is much larger than the atomic scale. UV/Vis spectrometry is used complementary to measure the collective optical properties. Both techniques can be used in situ to study self assembly's pathways.
A mesoporous material is a material containing pores with diameters between 2 and 50 nm. We are devising materials containing a mesoporous architecture to enhance size and shape selectivity for guest molecules or to template nanoparticles synthesis.