1. Center for Bio-Integrated Electronics; Northwestern University; Evanston IL 60208 USA
2. Institute of Photonics and Optoelectronics; National Taiwan University; Taipei 10617 Taiwan
3. Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
4. Department of Materials Science; Fudan University; Shanghai 200433 P. R. China
5. Department of Materials Science and Engineering; Department of Biomedical Engineering; Department of Neurological Surgery; Department of Chemistry; Department of Mechanical Engineering; Department of Electrical Engineering; and Department of Computer Science; Simpson Querrey Institute; Feinberg Medical School; Northwestern University; Evanston IL 60208 USA