1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.
2. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095, U.S.A.
3. Department of Physics, University of California, Berkeley, CA 94720, U.S.A.
4. European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
5. Department of Chemistry, University of California, Berkeley, CA 94720, U.S.A.
6. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, U.S.A.