1. Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, Lausanne 1015, Switzerland, Department of Material Science, Faculty of Engineering, Kyushu Institute of Technology, 1-1 Sensuicho, Tobata, Kitakyushu 804-8550, Japan, and Electron Microscopy, AQura GmbH, Rodenbacher Chaussee 4, D-63457 Hanau, Germany