Chemical transformations in ultrathin chalcogenide nanowires.

We have studied the chemical transformations in ultrathin chalcogenide nanowires with an aim to understand the parameters that control the morphology and crystal structure of the product. Ultrathin Te nanowires were transformed into Ag2Te nanowires with preservation of the single crystallinity. The Ag2Te nanowires were then converted into CdTe, ZnTe, and PbTe using cation-exchange reactions, and the CdTe nanowires were further transformed into PtTe2 nanotubes. On the basis of the solubility products of the ionic solids, the crystal structures of the involved solids, the reaction kinetics, and the reaction conditions for transformations, we were able to reach the following conclusions: (i) The solubility products of ionic solids can be used as a rough criterion to predict if the transformation is thermodynamically favorable or not. (ii) The morphological preservation of reactant nanowires is more sensitive to the change in length rather than the total volume in addition to the lattice matching between the reactant and product nanowires. (iii) The crystal structure resulting from a transformation should be determined by the free energy of formation and the stability of the products. (iv) The transformation involving small volume change or topotactic lattice matching is considered homogeneous along the entire length of the nanowires, preserving both the single crystallinity and the morphology of the reactant nanowires.