1. School of Physics; Trinity College Dublin; College Green Dublin 2 Ireland
2. Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN); AMBER at CRANN; Trinity College Dublin; College Green Dublin 2 Ireland
3. Materials Chemistry & Analysis Group; Department of Chemistry; University College Cork; Cork Ireland
4. Department of Physics; Chair for Applied Physics; Friedrich-Alexander-University Erlangen-Nürnberg; 91058 Erlangen Germany