[1] Pusan Natl Univ, Dept Nanoenergy Engn, Busan 46241, South Korea
[2] Pusan Natl Univ, Coll Nanosci & Nanotechnol, Busan 46241, South Korea
[3] Samsung Elect, Samsung Adv Inst Technol, Device & Syst Res Ctr, Suwon 16676, South Korea
[4] Tech Univ Munich, Phys Dept ECS, James Franck Str 1, D-85748 Garching, Germany
[5] Univ Illinois, Dept Mat Sci & Engn, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA