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 ...

Terahertz and optical study of monolayer graphene processed by plasma oxidation

Appl. Phys. Lett. 102, 131901 (2013); http://dx.doi.org/10.1063/1.4795526
(Received 7 February 2013; accepted 26 February 2013; published online 1 April 2013)

Authors: Kyujin Choi¹, Juhwan Lim², J. R. Rani², Hyong Seo Yoon², Juyeong Oh², Taeyoon Hong¹, Taewoo Ha¹, Byung Cheol Park¹, Kyung Ik Sim¹, Seong Chan Jun², and Jae Hoon Kim^1
1 Department of Physics and Institute of Physics and Applied Physics, +Yonsei University, Seoul 120-749, Republic of Korea 
² Department of Mechanical Engineering, +Yonsei University, Seoul 120-749, Republic of Korea 

Abstract

We report on our terahertz and optical study of monolayer graphene grown by chemical vapor deposition and processed by plasma oxidation. The plasma oxidation induces oxygen-related defects, and the resulting disorder increases the sheet resistance of graphene as measured via terahertz spectroscopy. The excitonic absorption peak weakens considerably and blue shifts upon plasma oxidation, resulting in higher transmittance in both the visible and ultraviolet regions. Our oxygen plasma-treated graphene also exhibits a free-carrier doping effect as confirmed by the blue shift of the Raman G band.

... Raman spectroscopy was performed with WITEC ALPHA300M Raman System (excitation at 532 nm, 2.33 eV). The VUV spectrophotometry was carried out with a Cary 5G spectrophotometer and THz-TDS with TeraView TPS Spectra 3000 ... 

More details at: http://apl.aip.org/resource/1/applab/v102/i13/p131901_s1?isAuthorized=no

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