1. Shandong Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, 250101 Jinan, China
2. Department of Materials Science and Engineering-Ångström, Uppsala University, 75121 Uppsala, Sweden
3. TdB Labs, 75121 Uppsala, Sweden
4. Department of Physics and Astronomy-Ångström, Uppsala University, 75120 Uppsala, Sweden