1. Max Planck Institute
of Microstructure Physics, 06120 Halle, Germany
2. Martin-Luther-Universität, Centre for Innovation Competence SiLi-nano, 06120 Halle, Germany
3. Physical
Department, St. Petersburg State University, 198504 St. Petersburg, Russia
4. St. Petersburg
Academic University RAS, 194021 St. Petersburg, Russia
5. St. Petersburg
State Polytechnical University, 195251 St. Petersburg, Russia
6. Institute
of Physics, Carl von Ossietzky University Oldenburg, 26129 Oldenburg, Germany