1. Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan, R.O.C
2. Graduate Institute of Science Education, National Kaohsiung Normal University, Kaohsiung 824, Taiwan, R.O.C
3. Department of Physics, National Kaohsiung Normal University, Kaohsiung 824, Taiwan, R.O.C
4. Institute of Physics, Academia Sinica, Taipei 115, Taiwan, R.O.C
5. Department of Applied Physics, National PingTung University of Education, Pingtung 900, Taiwan, R.O.C