[1] Swiss Fed Inst Technol, EPFL, Ceram Lab, CH-1015 Lausanne, Switzerland
[2] Res Ctr Julich, Peter Grunberg Inst, D-52425 Julich, Germany
[3] Res Ctr Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany
[4] Xi An Jiao Tong Univ, Sch Elect & Informat Engn, Int Ctr Dielect Res, Xian 710049, Peoples R China
[5] Silesian Univ, Inst Phys, PL-40007 Katowice, Poland