Posted in | Graphene

New Research Milestone Facilitates Creation of Scalable Crystalline Graphene Films

Transmission electron microscope images observed from the reduced graphene oxide films prepared by ethanol treatment at (a) 900ºC and (b) 1100ºC. For the high temperature treatment, the periodic bright spots are observed in the reduced graphene oxide films. This means that the crystallinity of the reduced graphene oxide is efficiently improved by high temperature treatment in ethanol environment. (Credit: Osaka University)

A team of researchers have discovered a process to repair graphene oxide (GO) structures that have a fault which make the material to exhibit low carrier mobility.

The deformed structures were repaired using a high-temperature reduction treatment in an ethanol environment. This led to the creation of a highly crystalline graphene film with superior band-like transport.

These results could have use in scalable production methods of highly crystalline graphene films.

Graphene is known for its superior electric conductivity, chemical stability, mechanical strength, and a large surface area. Its structure is made up of a one-atom-thick layer of carbon atoms. Researchers worldwide are working on the material’s synthesis and application to electronic gadgets due to its extraordinary attributes.

Graphene can be produced from graphene oxide (GO), a material produced using chemical exfoliation from graphite via oxidative treatment. However, this treatment causes the existence of oxygen-containing groups and faulty structures, which results in GO exhibiting low conducting properties.

Until now, carrier mobility, the fundamental indicator with which performance of a transistor is expressed, remained at a few cm2/Vs at most.

A team of researchers led by Ryota Negishi, assistant professor, and Yoshihiro Kobayashi, professor, Graduate School of Engineering, Osaka University; Masashi Akabori, associate professor, Japan Advanced Institute of Science and Technology; Takahiro Ito, associate professor, Graduate School of Engineering, Nagoya University; and Yoshio Watanabe, Vice Director, Aichi Synchrotron Radiation Center, have formulated a reduction treatment where the crystallinity of GO was considerably enhanced.

A substrate was coated by the researchers with one to three very thin layers of GO. They then added a small quantity of ethanol in up to 1100°C high temperature reduction process. Adding the carbon-based ethanol gas caused the successful restoration of the deformed graphene structure.

This was the first time a team of researchers were able to observe a band-like transport reflecting the inherent electric transport properties in chemically reduced GO films. Band-like transport can be defined as a conduction mechanism where the carriers make use of the periodic electric mechanisms in solid crystals as a transmission wave.

The band transport studied in this research achieved a carrier mobility of ~210 cm2/Vs, which is now the highest level ever observed in chemically reduced GO films.

The successful development of thin graphene films realized through the reduction technique has paved the way for their application in a varied set of electronic gadgets and sensors. The research findings form a milestone in the progress of scalable materials that use graphene’s superior physical properties.

This research was published in Scientific Reports (Nature Publishing Group) on July 1, 2016.

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