Oriented Metallic Nano-Objects on Crystalline Surfaces by Solution Epitaxial Growth.

Chemical methods offer the possibility to synthesize a large panel of nanostructures of various materials with promising properties. One of the main limitations to a mass market development of nanostructure based devices is the integration at a moderate cost of nano-objects into smart architectures. Here we develop a general approach by adapting the seed-mediated solution phase synthesis of nanocrystals in order to directly grow them on crystalline thin films. Using a Co precursor, single-crystalline Co nanowires are directly grown on metallic films and present different spatial orientations depending on the crystalline symmetry of the film used as a 2D seed for Co nucleation. Using films exposing 6-fold symmetry surfaces such as Pt(111), Au(111), and Co(0001), the Co heterogeneous nucleation and epitaxial growth leads to vertical nanowires self-organized in dense and large scale arrays. On the other hand, using films presenting 4-fold symmetry surfaces such as Pt(001) and Cu(001), the Co growth leads to slanted wires in discrete directions. The generality of the concept is demonstrated with the use of a Fe precursor which results in Fe nanostructures on metallic films with different growth orientations which depend on the 6-fold/4-fold symmetry of the film. This approach of solution epitaxial growth combines the advantages of chemistry in solution in producing shape-controlled and monodisperse metallic nanocrystals, and of seeded growth on an ad hoc metallic film that efficiently controls orientation through epitaxy. It opens attractive opportunities for the integration of nanocrystals in planar devices.

Solution epitaxial growth of cobalt nanowires on crystalline substrates for data storage densities beyond 1 Tbit/in2.

The implementation of nano-objects in numerous emerging applications often demands their integration in macroscopic devices. Here we present the bottom-up epitaxial solution growth of high-density arrays of vertical 5 nm diameter single-crystalline metallic cobalt nanowires on wafer-scale crystalline metal surfaces. The nanowires form regular hexagonal arrays on unpatterned metallic films. These hybrid heterostructures present an important perpendicular magnetic anisotropy and pave the way to a high density magnetic recording device, with capacities above 10 Terabits/in(2). This method bypasses the need of assembling and orientating free colloidal nanocrystals on surfaces. Its generalization to other materials opens new perspectives toward many applications.

Organometallic precursors of nano-objects, a critical view.

The synthesis of nanoparticles has experienced a huge development over the past 20 years. However, this development has remained relatively limited to a few classes of nanomaterials such as iron oxides, semi-conducting oxides, plasmonic nanoparticles (essentially Au) and quantum dots. In these cases, a physical chemistry approach and standard recipes allow a good control of the size and shape of the resulting nano-objects. However, organometallic precursors have emerged as an important class allowing the preparation of a large variety of nano-objects, concerning a large number of elements and displaying a clean and controllable surface and therefore good physical and chemical properties. This perspective article is mostly devoted to the research efforts carried out by our group on the search for new classes of precursors and on the importance of knowing their exact structure and the molecular chemistry involved prior to the fabrication of the nano-objects.