1. Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
2. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California 91125, USA
3. Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA
4. Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA