1. K. M. McGrath and S. M. Gruner, Department of Physics and Princeton Materials Institute, Princeton University, Bowen Hall, 70 Prospect Avenue, Post Office Box 708, Princeton, NJ 08544, USA.
2. D. M. Dabbs and I. A. Aksay, Department of Chemical Engineering and Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA.
3. N. Yao, Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA.