Acknowledgements

This research is financially supported by the National Key Scientific Instrument and Equipment Development Projects of China (No. 2012YQ040164) and the National Natural Science Foundation of China (Grant Nos. 61275127 and 91441130). The author would like to thank Prof. Xin Yu, Dr. Jiangbo Peng, and A/Prof. Jianlong Zhang et al. for providing many valuable insights and numerous help.
