Vapor-solid growth of Sn nanowires: growth mechanism and superconductivity.

A noncatalytic and template-free vapor transport process has been employed to prepare single-crystalline Sn nanowires with diameters of 10-20 nm. The growth of one-dimensional Sn nanowires follows the mechanism similar to the vapor-solid (V-S) mechanism. Two-dimensional square-shaped nanostructures were also found to form in the region of lower deposition temperatures. The rich morphology may be attributed to the competition in growth rate among different crystallographic planes. Structural characterization with high-resolution transmission electron microscopy showed that the nanowires and nanosquares grew in a preferential direction of [200]. The superconducting transition temperatures for Sn nanowires and Sn nanosquares were about 3.7 K, which was very close to that of bulk beta-Sn. Magnetization measurements showed that the critical magnetic fields for both Sn nanowires and Sn nanosquares increased significantly as compared to that of bulk Sn.