**Acknowledgements**

The project is supported by a New Zealand Marsden Grant, the National Natural Science Foundation of China (Grant NO 51401024) and Auckland UniServices project. The authors would like to thank the group members especially Weiwei Chen, Ying Ju, Shanghai Wei, Bo Hu and See Leng Tay, technical stuff in the Department of Chemical and Materials Engineering and the Research Centre of Surface and Materials Science for various assistances. We also want to express our gratitude to Mr Glen Slater, Chris Goode and technical stuff in Rigg Electro‐ plating Ltd.
