Origin of optical bandgap fluctuations in graphene oxide
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THE EUROPEAN PHYSICAL JOURNAL B
Colloquium
Origin of optical bandgap fluctuations in graphene oxide? Alessandro Henrique de Lima 1 , Camila Thomacelli Tavares 1 , Clemilda Corrˆea Soares da Cunha 1 , Nayton Claudinei Vicentini 1 , Giovani Romeu Carvalho 1 , Benjamin Fragneaud 1 , Indhira Oliveira Maciel 1 , Cristiano Legnani 1 , Welber Gianini Quirino 1 , Luiz Fernando Cappa de Oliveira 2 , Fernando Sato 3 , and Jo˜ao Paulo Almeida de Mendon¸ca 3,a 1
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Grupo de Nanociˆencias e Nanotecnologia - Nano, Departamento de F´ısica – UFJF, Juiz de Fora/MG 36036-900, Brazil N´ ucleo de Espectroscopia e Estrutura Molecular – NEEM, Departamento de Qu´ımica – UFJF Juiz de Fora/MG 36036-900, Brazil Laborat´ orio de Simula¸ca ˜o, Departamento de F´ısica – UFJF, Juiz de Fora/MG 36036-900, Brazil Received 27 November 2019 / Received in final form 6 April 2020 Published online 10 June 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. In this work, we explore the electrical, optical and spectroscopic properties of different Graphene Oxide (GO) samples focusing on new oxidative strategies to tune their physicochemical properties. Three types of GO samples were prepared by changing the oxidative conditions resulting in carbonyl-, epoxy- or hydroxyl-rich GO. These materials were characterized by UV-VIS absorption, Raman spectroscopy and Xray diffraction. The experimental results indicate that all samples exhibit oxidation and exfoliation degrees typical of graphene oxides obtained by using the modified Hummers’ method. The optical bandgap values were measured using the Tauc’s plot from UV-VIS data and showed that the stoichiometry of GO impacts the width of the bandgap. The carbonyl-rich sample presented the lowest gap around 3.20 ± 0.02 eV, while epoxy- and hydroxyl-rich GOs showed out gaps of about 3.48 ± 0.07 and 3.72 ± 0.05 eV, respectively. These experimental results are consistent with theoretical calculations of bandgaps obtained with coronene and circumcoronene GO models. The calculations were obtained using different theoretical approaches, such as: Huckel, PM3, AM1 and DFT. The present work suggests that a precise tuning of the optical bandgap of GOs can be achieved by only changing their stoichiometry thus allowing their use in a large range of electronic applications.
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Introduction
Graphene Oxide (GO) is a carbon-based nanomaterial prepared through the chemical oxidation of natural graphite in the presence of strong oxidants. This material has been identified much before pristine graphene [1] and was first reported in the XVII century by Brodie et al. [2]. Nowadays, GO is considered as one of the most important materials to obtain graphene [3,4]. Among many potential applications, GO can be used to produce reduced GO (rGO) for transparent conducting electrodes (TCEs), which has been, for instance, employed in the preparation of organic-light emitting diodes [5,6] (OLEDs) and organic photovoltaic devices [7,8] (OPVs). Other works also report
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