1. Faculty of Engineering and Natural Sciences, Tampere University, P. O. Box 541, 33101 Tampere, Finland
2. State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, Shaanxi Joint Key Laboratory of Graphene, School of Microelectronics, Xidian University, 2 South Taibai Road, Xi’an 710071, People’s Republic of China
3. Instituto de Investigação do Medicamento (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003 Lisboa, Portugal
4. Physics, Faculty of Science and Engineering and Center for Functional Materials, Åbo Akademi University, Porthansgatan 3, 20500 Turku, Finland