[1] Univ London Imperial Coll Sci Technol & Med, Dept Chem, London SW7 2AZ, England
[2] Univ London Imperial Coll Sci Technol & Med, Ctr Plast Elect, London SW7 2AZ, England
[3] UCL, Dept Chem, London WC1H 0AJ, England
[4] Univ London Imperial Coll Sci Technol & Med, Dept Phys, London SW7 2AZ, England
[5] Univ London Imperial Coll Sci Technol & Med, Dept Mat, London SW7 2AZ, England
[6] AWE, Reading RG7 4PR, Berks, England