[1] Chung Yuan Christian Univ, Dept Chem, Chungli 32023, Taiwan
[2] Chung Yuan Christian Univ, Dept Phys, Chungli 32023, Taiwan
[3] Chung Yuan Christian Univ, Ctr Nanotechnol, Chungli 32023, Taiwan
[4] Drexel Univ, Dept Chem, Philadelphia, PA 19104 USA