Secondary Facet-Selective Nucleation and Growth: Highly Oriented Straight SnO2 Nanowire Arrays on Primary Microrods

Recently, controlled growth of branched hierarchical crystals has been the focus of intensive research for their novel properties and potential applications. The key to synthesizing the branched nanostructures is to induce and control secondary nucleation on primary crystals. The metal catalysts and organic structure-directing agents are mainly utilized to induce the secondary nucleation and branch growth, however, nucleation sites are usually random because the metal catalysts and capping agents have been not controlled to deposit or etch on the expected facets of primary crystals. In this paper, we report that varying the ratio of oxygen to tin vapor in reaction can tune the growth rate of SnO2 along different directions in a vapor-solid (VS) process to alter the growth habit. By this new shape-controlled way, we can first control the synthesis of quasi-hexagonal primary microrods like SnO2 and then facet-selectively grow secondary nanobranches on them without use of any catalyst or surface modification. The controlled nucleation and the growth of nanowire arrays on primary crystals by this facile VS method just like SnO2 may provide a useful route for connecting nanobuliding blocks into some desired hierarchical nanostructures and nanodevices.