1. Electrical Engineering Division, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, United Kingdom
2. i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal
3. Holst Centre/TNO, High Tech Campus 31, 5656AE Eindhoven, The Netherlands
4. 252, Valley Drive, Kendal LA9 7SL, United Kingdom