1. CENTERA Laboratories, Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw 01-142, Poland
2. Nanotechnology Group, USAL-Nanolab, Universidad de Salamanca, Salamanca 37008, Spain
3. Nano-Device Laboratory, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
4. Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia