1. Barrer Centre Department of Chemical Engineering Imperial College London South Kensington Campus, Exhibition Road London SW7 2AZ United Kingdom
2. Department of Chemistry Imperial College London South Kensington Campus, Exhibition Road London SW7 2AZ United Kingdom
3. Current address: Department of Chemical Engineering University College London London WC1E 7JE United Kingdom
4. London Centre for Nanotechnology and Department of Materials Imperial College London South Kensington Campus, Prince's Consort Road London SW7 2BP United Kingdom
5. Current address: National High Magnetic Field Laboratory Tallahassee FL 32306 U.S.A.
6. Department of Physics University of Florida Gainesville FL 32611 U.S.A.