[1] Aalto Univ, Dept Micro & Nanosci, Tietotie 3, Espoo 02150, Finland
[2] Univ Autonoma Barcelona, Escola Engn, Dept Elect Engn, Campus UAB, E-08193 Bellaterra, Spain
[3] Tech Univ Chemnitz, Inst Phys, Reichenhainer Str 70, D-09126 Chemnitz, Germany
[4] Keysight Technol, Lyoner Str 20, D-60528 Frankfurt, Germany