Affiliation: | a Institute of Optoelectronic Sciences, National Taiwan Ocean University, 2, Pei-Ning Road, Keelung 20224, Taiwan, ROC b Department of Physics, Portland State University, P.O. Box 751, Portland, OR 97207-0751, USA c Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC d Department of Physics, National Taiwan University, Taipei 10617, Taiwan, ROC e Center of Nanostorage Research, National Taiwan University, Taipei 10617, Taiwan, ROC |