Terahertz, optical, and Raman signatures of monolayer graphene behavior in thermally reduced graphene oxide films

Journal of Applied Physics / Volume 113 / Issue 18 / ARTICLES / Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Authors: Juhwan Lim¹, Kyujin Choi², J. R. Rani¹, Jin-Seon Kim^3,4, Changgu Lee^3,4, Jae Hoon Kim², and Seong Chan Jun¹
1 Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Republic of Korea 
2 Department of Physics and Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Republic of Korea 
3 School of Mechanical Engineering, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, Republic of Korea 
4 Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Republic of Korea 

Abstract

We report on our joint spectroscopic study of the thermal reduction process of quasi-monolayer graphene oxide films grown on fused silica substrates by spin-coating. We estimate that about 65% of our film area consists of monolayer platelets of reduced graphene oxide, based on our quantitative analysis of the local atomic force microscopy topography. With thermal annealing under suitable conditions, clear signatures of monolayer graphene behavior were identified in the resonant excitonic absorption at 4.55 eV, the overall decrease in the visible-range transmission, the re-emergence of the Raman 2D band, the red-shift of the Raman G band toward the monolayer position, and the decrease in the optical sheet resistance in the terahertz range.

... The VUV, terahertz, and Raman measurements on our GO thin films, rGO thin films, and monolayer graphene grown by CVD were carried out with a grating spectrophotometer (Cary 5G), a terahertz time-domain spectrometer (TPS Spectra 3000, TeraView), and a WITEC ALPHA300M Raman ...