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Journal Articles

Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

Yamaguchi, Hisato*; Ogawa, Shuichi*; Watanabe, Daiki*; Hozumi, Hideaki*; Gao, Y.*; Eda, Goki*; Mattevi, C.*; Fujita, Takeshi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; et al.

Physica Status Solidi (A), 213(9), p.2380 - 2386, 2016/09

https://doi.org/10.1002/pssa.201532855

Times Cited Count：13 Percentile：52.49(Materials Science, Multidisciplinary)

We report valence-band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. The degree of oxygen functionalization was controlled by annealing temperature, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in the density of states around the Fermi level upon thermal annealing at 600 $^{circ}$ C. The result indicates that while there is an apparent bandgap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of bandgap closure was correlated with the electrical, chemical, and structural properties to determine a set of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of 500 $^{circ}$ C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to an as-synthesized counterpart.

Oral presentation

Real-time synchrotron radiation photoelectron spectroscopic observation of high temperature thermal anneal processes of oxidized graphene

Hozumi, Hideaki*; Yamaguchi, Hisato*; Kaga, Toshihide*; Eda, Goki*; Mattevi, C.*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, ,

In order to clarify the time evolution of the chemical bonding state during thermal reduction of graphene oxide (GO), real-time photoelectron spectroscopy was employed for observing the thermal reduction kinetics of GO. The GO was prepared by the modified Hummer method. The experiments were performed using the surface reaction analysis apparatus placed at the BL23SU of SPring-8. The XPS measurements were performed simultaneously during the annealing at 473 K, 673 K, 873 K, and 1073 K. The C1s photoelectron spectra are decomposed by 8 components. The - transition loss peak intensity is propotional to the intensity of sp $^{2}$ graphene components with temperature elevation. In addition, defect intensity increased in proportion with the sp $^{2}$ graphene intensity. These facts indicate that defects were formed on the graphene during reduction and these defects cause the recovery of electric conductivity, that is, the appearance of Fermi edge.

Oral presentation

Real time XPS observation of oxidized graphene reduction processes

Ogawa, Shuichi*; Yamaguchi, Hisato*; Hozumi, Hideaki*; Kaga, Toshihide*; Eda, Goki*; Mattevi, C.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, ,

no abstracts in English

Oral presentation