1. Department of Materials, Imperial College London, Prince Consort Road, South Kensington, London, SW7 2AZ, U.K.
2. Department of Chemical Engineering, Imperial College London, Imperial College Rd, South Kensington, London, SW7 2AZ, U.K.
3. SANKEN (Institute of Scientific and Industrial Research), Osaka University, Mihogaoka, Ibaraki, Osaka 567-0047, Japan