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

Abstract

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.

A Seed‐Mediated Approach for the Preparation of Modified Heterogeneous Catalysts

“…[15] Inspiredbythis approach, we took advantage of Co particles already immobilizedo nasupport, that is, Co particles of ac onventional FTS catalystp repared by as tandard impregnation method, and used them as seeds on which hcp-cobalt NRs could overgrow from as olution containingm olecular cobalt.I ndeed, someo fu sh ave recently shown that purely hcp Co NRs andn anowires( NWs) can be grown from as olution containing [Co{N(SiMe 3 ) 2 } 2 (thf)],L A, and HDA, on crystallographically oriented metallics ubstrates, which play the role of seeds for the epitaxialC og rowth. [16] These studies have demonstrated that the solution composition dictates the crystallographic structure andt he shape of the Co nanostructures, and this independently of the substrate nature and crystallographic orientation. Indeed,h cp Co NRs/NWshave been obtained in all cases, their growth startinge ither from (111)f cc or (0 001) hcp surfaces of various metallicf ilms, and even on the surface of bulk metals.…”

“…Indeed, hcp Co NRs/NWs have been obtained in all cases, their growth starting either from (1 1 1) fcc or (0 0 0 1) hcp surfaces of various metallic films, and even on the surface of bulk metals. Thus, by controlling the solution composition, the Co overgrowth could take place anisotropically on the surface of (1 1 1) fcc or (0 0 0 1) hcp six‐fold symmetry facets of the Co particles of the catalyst, which would play the role of seeds . To validate this approach, we first used a conventional 15 % Co/Al 2 O 3 –SiO 2 catalyst ( S BET =128 m 2 g −1 , pore volume=0.32 mL g −1 , mean pore diameter=10 nm) prepared as described in the Experimental Section, for which the particles presented a broad size distribution (Figure S3 in the Supporting Information).…”

Shape selection through epitaxy of supported platinum nanocrystals

“…We have previously shown that a wet-chemistry method that produces well-defined and homogeneously shaped nano-objects in solution can reproduce these nano-objects on a solid support by performing the reaction in the presence of this support. By this method it has been possible to epitaxially grow cobalt nanowires and iron nanocubes on crystallographically oriented metal surfaces, 9,10 as well as on bulk metal foams. 11 It was also shown that the epitaxial relationship between the support and the growing nanostructure determines the orientation of the nanostructure on the support surface, while the composition of the solution determines the nanostructure shape, which corresponds to the same shape obtained in solution in the absence of support, thus, to the same exposed facets.…”

Enhanced magnetocrystalline anisotropy in an ultra-dense array of air-exposed crystalline cobalt nanowires

“…They are obtained by adapting the seed-mediated solution phase synthesis of nanocrystals 7 to grow them epitaxially directly on crystalline thin films. 8 On Pt(111), this method leads to the epitaxial growth of vertical wires with the c-axis of the hexagonal compact (hcp) structure parallel to the NW axis. 9 The Co NWs spontaneously self-assemble into hexagonal arrays of 8 Â 10 12 NWs/in.…”

“…The array under study consists of metallic NWs of length L ¼ 1000 6 80 nm and diameter D ¼ 6.2 6 0.8 nm. 8 Each NW is naturally covered with organic surfactants. Small angle neutron scattering measurements on air-exposed NWs yield a center-to-center interwire distance of d ¼ 9.6 6 0.5 nm corresponding to a packing fraction P ¼ ðp=2 ffiffi ffi 3 p Þ Â ðD=dÞ 2 ¼ 0:38.…”