1 F.X. Campos, G.C. Weaver, C.J. Waltman, and S.R. Leone, Journal of Vacuum Science \& Technology B: Microelectronics and Nanometer Structures 10, (1992).
1 R.J. Levis, C.J. Waltman, L.M. Cousins, G.. Copeland, and S.R. Leone, Journal of Vacuum Science \& Technology A: Vacuum, Surfaces, and Films 8, (1990).