1. Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
2. Department of Chemistry and 4D LABS, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
3. Department of Applied Physics, Donghua University, Ren Min Road 2999, Songjiang, 201620 Shanghai, People's Republic of China