1. National Institute of Standards and Technology (NIST), Materials Science and Engineering Division; Gaithersburg MD 20899 USA
2. Towson University, Department of Physics, Astronomy and Geosciences; Towson MD 21252 USA
3. Los Alamos National Laboratory, Center for Integrated Nanotechnologies; Los Alamos NM 87545 USA
4. National Institute of Standards and Technology, Semiconductor and Dimensional Metrology Division; Gaithersburg MD 20899 USA