[1] Natl Tsing Hua Univ, Dept Phys, Hsinchu 30013, Taiwan
[2] Natl Taiwan Univ Sci & Technol, Dept Polymer Engn, Taipei 10607, Taiwan
[3] Acad Sinica, Inst Phys, Taipei 11529, Taiwan
[4] Nation Tsing Hua Univ, Nucl Sci & Technol Dev Ctr, Hsinchu 30013, Taiwan
[5] Univ Oxford, Inorgan Chem Lab, Dept Chem, Oxford OX1 3QR, England