1. Department of Materials Science and Frederick Seitz Materials Research Laboratory, University of Illinois, 104 S. Goodwin Avenue, Urbana, Illinois 61801, USA
2. EMPA, Laboratory for Nanoscale Materials Science, Überlandstrasse 129 CH-8600 Dübendorf, Switzerland and Department of Materials Science and Frederick Seitz Materials Research Laboratory, University of Illinois, 104 S. Goodwin Avenue, Urbana, Illinois 61801, USA
3. Department of Materials Science and Frederick Seitz Materials Research Laboratory, University of Illinois, 104 S. Goodwin Avenue, Urbana, Illinois 61801, USA and Messiah College, Department of Mathematical Sciences, P.O. Box 3041, One College Ave., Grantham, Pennsylvania 17027, USA