1. Electrical and Information Technology, Lund University, Box 118, SE-22100, Sweden
2. Department of Physics, University of Gothenburg, SE-41296 Gothenburg, Sweden
3. Division of Quantum Phases and Devices, School of Physics, Konkuk University, Seoul 143-701, South Korea
4. Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
5. Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
6. EaStCHEM, School of Chemistry, Edinburgh University, Edinburgh EH9 3JJ, Scotland