Published in Surf. Sci. Review and Letters 7, 601 (2000).
R. M. Feenstra,* Huajie Chen,* V. Ramachandran,* C. D. Lee,* A. R. Smith,** J. E. Northrup,*** T. Zywietz,**** J. Neugebauer**** and D. W. Greve***** *Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 **Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 ***Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304 ****Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany *****Department Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA 15213