[1] Indian Inst Technol Kharagpur, Sch Nanosci & Technol, Kharagpur 721302, India
[2] Indian Inst Technol Kharagpur, Adv Technol & Dev Ctr, Kharagpur 721302, India
[3] Uppsala Univ, Dept Chem, Angstrom Lab, PO Box 256, SE-75105 Uppsala, Sweden
[4] Indian Inst Technol Kharagpur, Mat Sci Ctr, Kharagpur 721302, India
[5] Indian Inst Technol Kharagpur, Dept Phys, Kharagpur 721302, India