Reduction dynamics of functionalized graphene
Hung Chieh Tsai1*, Hung-Wei Shiu2, Min-Chiang Chuang1, Andreas Johansson3, Chia-Hao Chen2, Mika Pettersson3, Wei Yen Woon1
1Department of Physics, National Central University, Taoyuan City, Taiwan
2National Synchrotron Radiation Research Center (NSRRC), Hsinchu, Taiwan
3Nanoscience Center, University of Jyväskylä, Jyväskylä, Finland
* presenting author:Hung-Chieh Tsai,
With all range of striking properties from high surface-to-volume ratio to extremely high electron mobility, graphene, the truly two-dimensional (2D) material, have gathered attention of researchers in various fields. However, the lack of band gap limits its applicability. Reduced form of graphene oxide (GO) is one of the most popular method to modify band gap through introduction of sp3 hybridization. The electric properties can be tuned by controlling the degree of oxidation. Nevertheless, reduction of GO done by thermal process cannot recover the excellent electronic properties of graphene due to residual oxygen-related functional groups. Hence, understanding the mechanisms for reduction of graphene oxide is necessary for both the application of graphene and interaction of functional groups on a 2D material.
Here, we report the reduction dynamics of micron-scaled defective graphene oxide patterns done on CVD-grown graphene by scanning probe lithography (SPL) and laser induced two-photon oxidation (LITPO), which provide two different mechanisms for functionalization. These patterns were subsequently reduced by the irradiation of a focused beam of soft x-ray. By in-situ monitoring the chemical configuration of the irradiated defects during the reduction process, the evolution of each oxygen functional group is resolved by scanning photoelectron microscopy (SPEM) and x-ray photoelectron spectra (XPS). Micro-Raman spectroscopy acquired before and after the reduction process revealed the structural evolution. Moreover, the characteristic time for each functional group dissociation/ formation process involved during reduction have been identified by the proposed reaction model using a coupled non-linear logistic equation. These finding giving the details physic picture of the reduction dynamics.

Keywords: functionalized graphene, scanning probe lithography, laser induced two-photon oxidation, reduction, photoelectron spectroscopy