[1] Indian Inst Technol Madras, Dept Phys, Madras 600036, Tamil Nadu, India
[2] Indian Inst Technol, Nano Funct Mat Technol Ctr, Madras 600036, Tamil Nadu, India
[3] Yonsei Univ, Dept Mat Sci & Engn, Seoul 120749, South Korea
[4] Indian Inst Technol, Dept Elect Engn, Microelect & MEMS Lab, Madras 600036, Tamil Nadu, India