1. Department of Electrical and Computer Engineering, Sungkyunkwan University, Jangan-Gu, Suwon, Gyeonggi-do 16419, South Korea
2. Department of Chemical Sciences, University of Johannesburg, Doornfontein, 2028, Johannesburg, South Africa
3. Center for Nanomaterials Science Research, University of Johannesburg, Doornfontein, 2028, Johannesburg, South Africa