TEM studies of the in-situ growth of silver metal nanowires from zeolites
We believe that the production of metal nanowires is triggered by the reduction of silver cations within the zeolite under the electron beam; the ease of reduction of silver-exchanged zeolites to form silver clusters and small metal particles is well documented (Sun and Seff 1994). The mechanism for the formation of wires instead of particles cannot be fully understood until substantially more experimental data has been collected. However, on the basis of evidence obtained to date, we can propose an outline picture of the formation mechanism (Fig. 4), which comprises several distinct steps. Our studies have shown that the migration of silver within the zeolite under the influence of the electron beam leads to areas of high metal concentration in parts of the zeolite crystal. Local disruption of the zeolite framework in these areas results in the formation of mesopores that template the formation of silver nanorods. Ultimately, the breaching of the crystallite surface by a silver-filled mesopore (Fig. 3b) allows silver to be extruded from the zeolite in the form of a nanowire. It is likely that charging of the silver under the electron beam leads to the attraction of further silver cations to these mesopores, ensuring a ready supply of silver to the growing nanowires.