1. 1Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, R.O.C.
2. 2Department of Electrical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, R.O.C.
3. 3Molecular Imaging Center, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, R.O.C.
4. 4Department of Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0851, Japan