[1] Nanotec Elect SL, Ctr Empresaial Euronova, E-28049 Madrid, Spain
[2] Univ Autonoma Madrid, Dept Fis Mat Condensada, Lab Nuevas Microscopias, E-28049 Madrid, Spain
[3] Univ Murcia, Fac Quim, Dept Fis, E-30100 Murcia, Spain
[4] Univ Autonoma Madrid, Dept Fis Mat Condensada, Dept Fis, E-28049 Madrid, Spain
[5] Univ Autonoma Madrid, Dept Fis Mat Condensada, Lab Neuvas Microscopias, E-28049 Madrid, Spain
[6] CSIC, Inst Ciencias Mat, E-28049 Madrid, Spain