Formation of three-dimensional nano-trees with perpendicular branches by electrodeposition of CuSn alloy

• We found a formation of three-dimensional nano-tree-like structures consisting of CuSn nanowires.
• The CuSn nanotrees were formed by co-electrodeposition method using constant voltage.
• Addition of Polyethylene glycol was important for formation of nanotree structure.

Three-dimensional nano-tree-like structures consisting of single-crystalline CuSn alloy nanowires branching perpendicularly from their parent branches were observed. The nano-trees were formed by constant potential co-electrodeposition of Cu and Sn. The geometry of the branches had a four-fold symmetry around the parent branch, which originated from the crystalline structure of the mother CuSn crystal. XRD and TEM analysis revealed that the nanowire branches consisted of single-crystalline γ-CuSn with 〈100〉 preferred growth directions. The addition of polyethylene glycol (PEG) with a molecular weight of 1000 in the plating bath is essential for the formation of the nano-tree structure. It is speculated that adsorbed PEG molecules on CuSn crystal planes with high Miller indices suppress CuSn alloy deposition, enhancing anisotropic growth of the CuSn crystal to form the nano-tree structure.