1. Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC), Campus UAB, 08193 Bellaterra, Barcelona, Spain
2. Institut Catala de Nanociencia i Nanotecnologia (ICN2), Campus UAB, 08193 Bellaterra, Barcelona, Spain
3. Consejo Superior de Investigaciones Cientificas (CSIC), Campus UAB, ICN2 Building, 08193 Bellaterra, Barcelona, Spain