1. Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland
2. Oxford Instruments Analytical Oy, Tietotie 3, 02150 Espoo, Finland
3. VTT Microelectronic Systems, Micronova, P.O. Box 1000, FI-02044 VTT Espoo, Finland
4. Microelectronics Research Center, The University of Texas at Austin, Austin, Texas78758, United States