1. Department
of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, United States
2. ICN2-Institut
Català de Nanociència i Nanotecnologia, Campus, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
3. Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic
4. Materials
Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States