1. Center for Physical Sciences and Technology, 01180, A. Goštauto 11, Vilnius, Lithuania
2. Walter
Schottky Institut, Physik Department, and Center of Nanotechnology
and Nanomaterials, Technische Universität München, Garching, 85748, Germany
3. Institute
for Nanoelectronics, Technische Universität München, Munich, 80333, Germany