[1] Natl Chiao Tung Univ, Dept Electrophys, Hsinchu 30010, Taiwan
[2] Chung Yuan Christian Univ, Dept Phys, Chungli 32023, Taiwan
[3] Chung Yuan Christian Univ, Ctr Nanotechnol, Chungli 32023, Taiwan
[4] Chung Yuan Christian Univ, R&D Ctr Membrane Technol, Chungli 32023, Taiwan
[5] Natl Changhua Univ Educ, Dept Phys, Changhua 50058, Taiwan
[6] I Shou Univ, Dept Mat Sci & Engn, Kaohsiung 840, Taiwan