1. Materials Science and Engineering Division Material Measurement Laboratory National Institute of Standards and Technology Gaithersburg MD 20899 USA
2. Department of Electrical and Computer Engineering George Mason University 4400 University Drive Fairfax VA 22030 USA
3. Department of Electrical and Computer Engineering Johns Hopkins University 3400 North Charles Street Baltimore MD 21218 USA
4. Department of Electrical and Computer Engineering The George Washington University Washington DC 20052 USA
5. Semiconductor and Dimensional Metrology Division Physical Measurement Laboratory National Institute of Standards and Technology Gaithersburg MD 20899 USA