1. Department of Physics, Umeå University, 901 87 Umeå, Sweden
2. Department of Chemistry, Umeå University, 901 87 Umeå, Sweden
3. Department of Chemistry − Ångström Laboratory, Uppsala University, 751 20 Uppsala, Sweden
4. College of Materials, Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen, Fujian 361005, China