Copyright (1998) American Vacuum Society. This
article may be downloaded for personal use only.
Any other use requires prior permission of the author and the
American Vacuum Society.
The following article appeared in A. R.
Smith et al., J. Vac. Sci. Technol. B 16, 2242
(1998)
and may be found at https://doi.org/10.1116/1.590156.