Vapor phase growth of free-standing palladium nanorods

Large-area free-standing palladium (Pd) nanorods were grown on sapphire substrate successfully by simply annealing Pd sheet in air at 1 atm. The Pd nanorod density was estimated to be about 1×106 cm−2 and the longest Pd nanorod grown at an angle on sapphire was over a few tens micrometers long. The Pd nanorods were found to grow preferentially along [111] and [110] directions from the transmission electron microscopy study. From the ample results of SEM images coupled with the kinetics data, we observed that Pd particles growth obeyed the classical ripening process during the initial short annealing time, and then followed a vapor–solid (VS) growth mode, leading to the formation of Pd nanorods in the later stage of annealing. The measured activation energy of Pd nanorods growth suggests that the Pd nanorods were formed by the surface diffusion of Pd adatoms coming from the Pd vapor. The use of present simple thermal annealing processes in the growth of free-standing Pd nanorods on large area substrate has potential for the future micro/nano-scale device fabrication.

► Free-standing Pd nanorods were prepared successfully by simple annealing in air.
► Vapor–solid growth model is proposed to explain the growth behavior of Pd nanorods.
► Kinetic studies of anisotropic Pd nanorod growth were discussed by the statistical method.