1. Division of Solid State Physics, Department of Materials Science and Engineering, Uppsala University, Uppsala SE-751 03, Sweden
2. Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg SE-412 96, Sweden
3. Division of X-ray Photon Science, Department of Physics and Astronomy, Uppsala University, Uppsala SE-751 20, Sweden
4. Division of Solid-State Electronics, Department of Electrical Engineering, Uppsala University, Uppsala SE-751 21, Sweden