1. Henan Province Engineering Research Center of Smart Micro‐nano Sensing Technology and Application School of Physics and Electronics Henan University Kaifeng 475004 P. R. China
2. School of Physics and Electronics Henan University Kaifeng Henan 475004 P.R. China
3. Waterloo Institute for Nanotechnology and Department of Electrical and Computer Engineering University of Waterloo Waterloo ON N2L3G1 Canada