1. Institute for Polymer Materials (POLYMAT) and Grupo de Ingeniería Química, Departamento de Química Aplicada, Facultad de Ciencias Químicas, The University of the Basque Country, Apdo. 1072, ES-20080 Donostia-San Sebastián, Spain; Department of Physics, University of Surrey, Guildford GU2 7XH, U.K.; and University of Surrey Ion Beam Centre, Guildford GU2 7XH, U.K.