Key Laboratory of Low-Dimensional Materials and Application Technology;
Xiangtan University;
Xiangtan 411105;
Department of Applied Physics and Materials Research Centre;
Hong Kong Polytechnic University;
Hung Hom;
Kowloon;
Hong Kong;
China;
School of Physics&Optoelectric Engineering;
and Guangzhou Higher Education Mega Center;
Guangdong University of Technology;
Guangzhou 510006;