1. State Key Laboratory of Electronic Thin Film and Integrated Devices; University of Electronic Science and Technology of China; Chengdu; 610054; P. R. China
2. Arkansas Institute of Nanoscale for Nanoscale Mater. Sci. Eng.; University of Arkansas; Fayetteville; AR; 72701; USA
3. College of Electronics and Information; Kwangwoon University; Nowon-gu; Seoul; 139-701; South Korea