Acknowledgments
The works at Penn State University was supported by the US Department of Energy, Division of Materials Sciences, under Grant No. DE-FG02-07ER46410. The work at Jozef Stefan Institute was supported by the Slovenian Research Agency. The authors thank B. Neese, B. Chu, Y. Wang, and E. Furman for their contributions to ECE work and Xiaoshi Qian for his assistance in the preparation of manuscript.