Studies on Surface Facets and Chemical Composition of Vapor Grown One-Dimensional Magnetite Nanostructures

Investigations on shape and chemical composition of one-dimensional magnetite nanostructures grown by a catalyst-assisted vapor phase procedure are reported. Intrinsic crystal chemistry (preferred growth of most stable surfaces) could be modulated by seeding the magnetite growth through Au nanoclusters, which. led to elongated nanostructures (VLS mode); however, the structures have similar facets as observed in uncatalyzed growth. Geometric and energetic contributions to the evolution of the predominately observed {111} surface facets are discussed on the basis of high-angle annular dark field (HAADF) images and electron energy loss spectroscopy (EELS). The Fe:O stoichiometry in magnetite nanowire was determined by EELS, which manifested the reproducibility of nanowire growth by molecule-based CVD and the slightly nonstoichiometric nature of magnetite (Fe3O4-0.15). In combination with HAADF-TEM techniques, Au nanoclusters were identified on the surface of single-crystalline nanowires, which ably result from the surface diffusion of the catalyst (Au) material. In addition, core-shell SnO2/Fe3O4 1 D nanostructures were fabricated by sequential deposition of Sri and Fe precursors. Cross-sections of the coaxial nanostructures revealed polycrystalline magnetite shells on single-crystalline SnO2 wires constituted by well-defined single-crystalline facetted grains of slightly nonstoichiometric magnetite.