1. School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, United States
2. Birck Nanotechnology Center, Center for Implantable Device, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
3. Department of Biological Sciences, Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, Indiana 47907, United States
4. Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
5. X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States