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This article has been retracted. A statement of retraction is published in Nano Volume 11, Issue 12 (2016).

This article had been submitted by one of the authors, Huijun Cheng, without the consent of the other authors, including the one who is in charge of the project. It is an inappropriate conduct and violates the scienti¯c rule of publishing papers. We regret that this was not detected during the review process, and that this article was accepted for publication in the journal. In view of the above, the board has decided to retract the publication of this paper in NANO.