The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copied to the public, and perform publicly and display publicly, by or on behalf of the Government. This work was carried out by the use of the Center for Nanoscale Materials (ANL/CNM). Y. Sun is grateful to Prof. John A. Rogers (University of Illinois at Urbana-Champaign) for allowing the use of the facilities in his research group. We also thank Qing Cao (University of Illinois at Urbana-Champaign) for the help in device fabrication. Devices were fabricated partially using the Microfabrication and Crystal Growth Facility in Frederick Seitz Materials Research Laboratory, University of Illinois, which is partially supported by the U.S. Department of Energy under Grant No. DEFG02-91-ER45439. Supporting Information is available online from Wiley InterScience or from the authors.