1Department of Physics, University of California at Berkeley,
2Advanced Light Source Division, Lawrence Berkeley National Laboratory,
3Materials Science Division, Lawrence Berkeley National Laboratory,
4Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5These authors contributed equally to this work.
6Present address: Department of Photonics and Institute of Electro-optical Engineering, National Chiao Tung University, Hsinchu, Taiwan 30010.
Correspondence and requests for materials should be addressed to F.W. ([email protected]).
Received 26 February 2009; accepted 30 April 2009
The authors declare no competing financial interests.
This work was supported by the Office of Basic Energy Sciences, US Department of Energy under contract DE-AC03-76SF0098 (Materials Science Division) and contract DE-AC02-05CH11231 (Advanced Light Source). F.W., Y.Z. and T.-T.T. acknowledge support from a Sloan fellowship, a Miller fellowship and a fellowship from the National Science Council of Taiwan, respectively.
