Single crystalline nanowires of lead: Large-scale synthesis, mechanistic studies, and transport measurements

A solution-phase, precursor method has been demonstrated for the large-scale synthesis of single crystalline nanowires of lead with uniform diameters in the range 50-90 nm and lengths up to several millimeters. In a typical procedure, the nanowires were synthesized by refluxing a mixture of Pb(CH ₃COO) ₂·3H ₂O and poly-(vinyl pyrrolidone) (PVP) in ethylene glycol under N ₂ for 90 min. Elemental lead was generated as a result of thermal decomposition of the precursor salt. Electron microscopic studies indicated that a solution-liquid-solid (SLS) growth mechanism was responsible for the nucleation and growth of lead atoms into single crystalline nanowires. When the hot reaction solution was injected into a cold ethanol bath through a syringe needle, bundles made of uniaxially aligned lead nanowires were formed. It was found that both composition and morphology of the product had a strong dependence on the reaction conditions that included the molar ratio between PVP and lead acetate, the reaction temperature, and the environment (nitrogen versus air). As the parameters were varied, nanostructures with a range of morphologies and compositions were observed as the products. Transport measurements on individual lead nanowires (as thin as ∼50 nm in diameter) suggest a transition to the superconducting state around 7.13 K, a temperature similar to the value (7.20 K) reported for bulk lead.