1. Department of Applied Physics The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong
2. Electrical and Computer Engineering University of California—Davis Davis California 95618 USA
3. Department of Electrical, Electronic and Computer Engineering Gifu University Gifu 501‐1193 Japan
4. The Norwegian Colour and Visual Computing Laboratory NTNU‐Norwegian University of Science and Technology Gjøvik N‐2815 Norway
5. Farm Technology Group Wageningen University Wageningen The Netherlands
6. Geballe Laboratory for Advanced Materials Department of Materials Science and Engineering Stanford University Stanford CA 943905 USA