ytterbium nanoparticles: properties, recent synthesis, developments and prespectives

Material science interest is more and more directed to the synthesis and characterization of nano-sized particles. This interest is justified by the fact that the reduction of the particle size of a given material to the nanometer scale causes the rising up of exotic properties that are not present in the bulk state due to size-dependent quantum effects and huge increase of the interfacial species. Further striking features can be gained by controlling nanoparticle shape or through the building up of spatially ordered mono-, bi- and three-dimensional nanoparticle arrays. Then, the wise selection of the nanoparticle synthetic strategy offers the possibility of preparing a wide class of novel materials and devices for specialised applications. In this ambit, much effort has been directed to set up efficient protocols for nanoparticle synthesis and spatial organization. In particular, since they tend to spontaneously grow and are highly reactive, an useful synthetic route should allow fine size and shape control and nanoparticle passivation. Among all the materials which can benefit from their reduction to the nanoparticle state, Yb is of interest due to its electronic configuration ([Xe] 4f145d06s2) in the ground state (1S0) and the related physico-chemical properties such as low work function (2.63 eV), high electron injection performance in electroluminescent devices, long range magnetic order, valence fluctuations and superconductivity of some of ytterbium-based intermetallics. However, an effective synthetic procedure of Yb-based nanostructures should take into account its chemistry. In fact, it has a strong tendency to be in oxidised states and its powders can easily enflame in contact with air. This implies that its preparation through chemical reduction processes requires very drastic conditions and explains why investigations on the synthesis and characterization of nanosized Yb are almost absent in the literature. On the other hand, top-down approaches as laser ablation of metal target in liquid environment, although successfully employed for the preparation of noble metal nanocolloids, revealed not efficient in the case of Yb due to a weak nanoparticle stabilization and post-ablation coalescence/aggregation processes. To face this problem, we set up a novel preparation by laser ablation of bulk Yb target immersed in some selected reverse micellar solutions. This method, combining the advantages of top-down (high purity, no side products) and bottom-up (compartimentalising/stabilizing media) strategies, proved to be efficient in the controlled synthesis of nanosized Yb allowing, after evaporation of the organic solvent, spatial organization of nanoparticles in the surfactant matrix. Moreover, the proposed method allows, by changing the experimental conditions (surfactant nature and concentration, laser fluence, presence of nanoparticles on which Yb can be deposited, etc), the preparation of different varieties of Yb-based nanostructures. The aim of this contribution is to furnish to the reader a panoramic view of this research field and to highlight its potentialities for the preparation of Yb-based nanostructures.