1. Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794; Department of Physics, North Carolina State University, Raleigh, North Carolina 27695; Stanford Synchrotron Radiation Lab, Stanford, California 94209; ExxonMobil Research and Engineering Company, Annandale, New Jersey 08801; and Department of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel