1. Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FIN-00076 Aalto, Espoo, Finland
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. Institute of Materials, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
4. Mechanical Engineering Department, University of California, Berkeley, California 94720, USA
5. Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong
6. US Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783, USA