[1] Ecole Polytech Fed Lausanne, Swiss Fed Inst Technol, Ceram Lab, CH-1015 Lausanne, Switzerland
[2] Elect Res Ctr Julich, Peter Grunberg Inst, D-52425 Julich, Germany
[3] Elect Res Ctr Julich, Ernst Ruska Ctr Microscopy & Spect, D-52425 Julich, Germany
[4] Xi An Jiao Tong Univ, Sch Elect & Informat Engn, Xian 710049, Peoples R China