Tescan MIRA3 FEG SEM
The authors acknowledge the University of Michigan College of Engineering for financial support and the Michigan Center for Materials Characterization for use of the instruments and staff assistance.

Fisher Scientific Nova 200 Nanolab
The authors acknowledge the financial support of the University of Michigan College of Engineering and NSF grant #DMR-0320740, and technical support from the Michigan Center for Materials Characterization.

JEOL 2010F
The authors acknowledge the financial support of the University of Michigan College of Engineering and NSF grant #DMR-9871177, and technical support from the Michigan Center for Materials Characterization.