1. Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
2. Semiconductor Physics, Technische Universität Chemnitz, 09107 Chemnitz, Germany
3. Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
4. Department of Materials for Nanoelectronics, Technische Universität Chemnitz, 09107 Chemnitz, Germany
5. Solid Surfaces Analysis, Technische Universität Chemnitz, 09107 Chemnitz, Germany
6. Leibniz Institute for Solid State Materials Research, IFW Dresden, Helmholtz Straße 20, 01069 Dresden, Germany