In Situ Fabrication of Inorganic Nanowire Arrays Grown from and Aligned on Metal Substrates

The full potential of nanotechnology can be unleashed only when one is able not only to synthesize a rich variety of nanoscale building blocks but also assemble them into various patterns at the supramolecular and supracluster levels. In particular, the application of nanoparticle and nanowire materials often requires their assembly in the form of thin films, preferably on conductive surfaces for electrical addressing, control, and detection. Although a dazzling array of nanostructures has been fabricated by bottom-up approaches, one of the contemporary challenges is to assemble these nanostructures so that they introduce and realize functionalities. An alluring avenue is to simultaneously accomplish both the nanostructure synthesis and assembly on a useful substrate in a parallel fashion, affording the advantages of simplicity, low cost, and high throughput. In this Account, we review our recent work on growing inorganic nanowires (for example, metal sulfides, metal oxides, and so forth) directly from and on metal substrates in arrays without using templates and catalysts. This method of engineering nanowire arrays on metal substrates integrates the nanowire synthesis and assembly into a parallel process, both in time and in space, by exploiting in situ chemistry on the metal substrates. Both gas-phase and solution-phase approaches have been developed to synthesize the aligned nanowires; here, full advantage is taken of interfacial kinetics of restricted diffusion and surface-specific reactions, often accompanied by new interfacial growth mechanisms. The setting of nanowire arrays on metal substrates has allowed exploration of their application potentials in areas such as field electron emission and chemical sensing. The approaches described here are general, and we predict that they will be extended to more inorganic materials, such as metal halides. Moreover, as more control is achieved with synthetic methods, inorganic nanowire arrays should provide unusual magnetic, optical, and electronic properties for nanostructural engineers willing to confront the attendant challenges. Accordingly, applications for which there is a current impetus for progress, such as solar cells or lithium ion secondary batteries, might well be addressed with this methodology.