The surfaces of nanoparticles that were obtained through “soft chemistry” are different than those obtained through dry processes. The introduction of ligands, polymers, and surface-active agents into a solution enables the size of the nano-objects to be controlled. The selective inhibition of the growth of certain crystal faces, induces anisotropies and new textures. If the presence of functional, organic molecules can cause contamination of materials, an innovative use would enable multifunctional organic-inorganic hybrid nanomaterials to be created.
The organic functions enable nano-objects to be assembled (particles, clusters, mono-layers, etc.) through diverse reactions (coupling, polymerisation, hydrosylation, etc.) by means of chemical, thermal or photonic stimuli.
The approach that consists of constructing the interface in situ offers more flexibility in the choice and definition of interfaces, and thus in the access to multifunctional materials.
Over and above of the “one material – one function” concept, it has become possible to cause numerous functions to interact from the same structure. A property can modulate another, or the co-existence of two or more properties may create new ones. This modulation of physical properties under the effect of external stimuli is being studied in different French laboratories, and today has become a common research theme.
The following topics merit particular attention :
The influence on the properties of parameters such as temperature, pressure, or even magnetic field, is commonly studied. This research deserves to be pursued, with the perspective of developing nano-sensors. The photo-magnetism that consists of addressing, then modulating the magnetic properties of materials through optical processes, constitutes a new path of research. The use of photo-induced phenomena (spin transition) and the transfer of electrons or the oxidation-reduction at the origin with effects on the macro- or mesoscopic scale (diamagnetic /ferromagnetic transition) is a subtle means of obtaining switchable materials.
The implementation of materials that are capable of combining magnetism with one or several other properties such as electric conductivity, and linear or non-linear optics is a second characteristic that has begun to emerge. For example, the packing of ferromagnetic (cobalt) nanoparticles that are functionalised by organic ligands, should give way to magneto-resistive properties through tunneling effect.