1. College of Science
2. Institute of Materials Physics and Chemistry
3. Nanjing Forestry University
4. Nanjing 210037
5. P. R. China
6. Department of Physical and Chemical Sciences
7. University of L'Aquila
8. 67100 L'Aquila
9. Italy
10. CNR-IMM Istituto per la Microelettronica e Microsistemi