Session:

Over the last years, several techniques have been developed for the production of graphene, such as direct physical exfoliation of graphite and epitaxial growth from SiC surfaces [1, 2,3]. Regardless of the adopted producing protocol, the resulting GO is an insulating material of both physical and chemical characteristics very different from those of pristine graphene. Due to this, the implementation of processes able to efficiently remove the presence of oxygen-containing functional groups is imperative to convert the GO properties as close as possible into those of pristine graphene. Generally, these cleaning processes are called “reduction”, and the resulting sample “reduced GO” (rGO). Here we report on water (H₂O) and carbon oxides (CO and CO₂) effusion from multilayered graphene oxide (GO) films during thermal reduction. The effusion of molecules as a function of temperature was monitored through the thermal desorption spectroscopy (TDS) technique in GO thin films prepared by evaporating a colloidal solution of GO at 70 °C. This method of preparation of GO films ensures a homogeneous GO deposition on different substrates and reduces the presence of adsorbed/trapped H₂O molecules between adjacent GO planes. That allows the observation of additional effusion mechanisms, which would be otherwise masked by a strong signal due to effusion of adsorbed/trapped H₂O molecules. Thermal reduction process, ranging from room temperature to ~1000 °C, was performed in a high-vacuum system with a mass spectrometer to monitor the outgassed species in real time. A collective outgassing of H₂O, CO₂, CO species is observed and centered at approximately 230°C. Above 400°C, CO₂ and CO are the only observed outgassed species. Multiple origins for water outgassing were inferred from the TDS spectrum asymmetry, revealing an intricate superposition of mechanisms. The thermal treatment also reduces both the GO interlayer separation and the film surface roughness.

Acknowledgements:
BYD Energy Brazil, FAPESP and CNPq.

References:
[1] K.S. Novoselov, A.K. Geim, S. V Morozov, D. Jiang, Y. Zhang, S. V Dubonos, I. V Grigorieva, A.A. Firsov, Science 306 (2004) 666–669.
[2] C. Virojanadara, M. Syväjarvi, R. Yakimova, L.I. Johansson, A.A. Zakharov, T. Balasubramanian, Phys. Rev. B 78 (2008) 1–6.
[3] M. Sprinkle, M. Ruan, Y. Hu, J. Hankinson, M. Rubio-Roy, B. Zhang, X. Wu, C. Berger, W.A. de Heer, Nat. Nanotechnol. 5 (2010) 727–31.

Co-Author(s): Douglas da Silva (UNICAMP), Gustavo Viana (UNICAMP), Rafael Merlo (UNICAMP), José da Silva Filho (UNICAMP)

Francisco Marques

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