Low temperature melting of copper nanorod arrays

We report the melting of nanorod arrays of copper at temperatures much lower than its bulk melting point (1083°C). The Cu nanorods were produced by an oblique angle sputter deposition technique through a physical self-assembly mechanism due to the shadowing effect. The as-deposited nanorods were ∼2300nm in length, ∼100nm in diameter, and separated from each other with gaps varying between ∼10 and ∼30nm. The melting process was investigated through the analysis of scanning electron microscopy, transmission electron microscopy, and x-ray diffraction measurements. Start of premelting (or surface melting) has been observed to occur at annealing temperature ∼400°C under vacuum (10−6Torr). As the temperature was raised the arrays of Cu nanorods started to coalesce and formed a dense continuous film with a (111) texture at ∼550°C. The results of this work may be useful for low temperature soldering applications.