1. nano analytik GmbH, 98693 Ilmenau, Germany
2. Department of Micro- and Nanoelectronic Systems, Technische Universität Ilmenau, 98693 Ilmenau, Germany
3. Department of Materials Science and Engineering, University of California, Berkeley, California 94720
4. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720