Before revision: Q. Cai, B. Ledden, E. Krueger, J. Golovchenko, and J. Li, Journal of Applied Physics, 100 (2006) Q. Cai, B. Ledden, E. Krueger, J. Golovchenko, and J. Li, Journal of Applied Physics, 100 (2006) .
After revision: Q. Cai, B. Ledden, E. Krueger, J. Golovchenko, and J. Li, Journal of Applied Physics, 100 (2006) .