1. Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
2. Plessey Semiconductors, Tamerton Road, Plymouth PL6 7BQ, United Kingdom
3. Experimental
Techniques Centre, Brunel University, Uxbridge UB8 3PH, United Kingdom
4. Gatan U.K., 25 Nuffield Way, Abingdon, Oxon OX14 1RL, United Kingdom