[1] Karlsruhe Inst Technol, Dept Inst Funct Interfaces, Hermann von Helmholtz Pl 1,B330, D-76344 Eggenstein Leopoldshafen, Germany
[2] NIST, Semicond & Dimens Metrol Div, 100 Bur Dr, Gaithersburg, MD 20899 USA
[3] Old Dominion Univ, Dept Elect & Comp Engn, Norfolk, VA 23529 USA
[4] Newport News Thomas Jefferson Natl Accelerator La, Appl Res Ctr, Newport News, VA 23606 USA