[1] Natl Tsing Hua Univ, Dept Mat Sci & Engn, Hsinchu, Taiwan
[2] Natl Synchrotron Radiat Res ctr, Hsinchu, Taiwan
[3] Natl Tsing Hua Univ, Dept Phys, Hsinchu, Taiwan
[4] Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10764, Taiwan
[5] Rutgers State Univ, Dept Chem & Phys, Piscataway, NJ 08854 USA