[1] Oak Ridge Natl Lab, Div Mat Sci & Technol, Oak Ridge, TN 37831 USA
[2] Cameca Instruments Inc, Madison, WI 53711 USA
[3] Iowa State Univ, Dept Mat Sci & Engn, Ames, IA 50011 USA
[4] Univ Sydney, Australian Ctr Microscopy & Microanal, Sydney, NSW 2006, Australia