1. Department of Chemistry and Biochemistry, UC San Diego, La Jolla, California 92093, U.S.A.
2. Materials Science and Engineering Program, UC San Diego, La Jolla, California 92093, U.S.A.
3. Earth and Planets Laboratory, Carnegie Institution for Science, Washington, D.C. 20015, U.S.A.
4. Department of Physics, University of Lille, 59655 Villeneuve d’Ascq, France