a
School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon 440-746, Republic of Korea
E-mail: kimsw1@skku.edu
;
Fax: +82-31-290-7381
b
Samsung Advanced Institute of Technology (SAIT), Samsung Electronics, Yongin 446-712, Republic of Korea
c
School of Chemical Engineering and Bioengineering, University of Ulsan, Ulsan 680-749, Republic of Korea
d
SKKU Advanced Institute of Nanotechnology (SAINT), Center for Human Interface Nanotechnology (HINT), SKKU-Samsung Graphene Center, Sungkyunkwan University (SKKU), Suwon 440-746, Republic of Korea