Graphene variants promise new possibilities
Come: Chinese Academy of Sciences Date: 2018-01-11 17:05:59
Craciun has a vision: to make it as easy to fabricate a circuit on graphene as it is to sketch one with pencil and paper – in short, to make graphene live up to its name. The vision was realized in 2011, when Craciun group found that an electron beam can be used to selectively reduce regions of fluorinated graphene – an electrical insulator – to pure, conductive graphene. This means that conducting patterns of any given shape can be inscribed in a fluorinated host, allowing the design of complex, all-graphene circuits and components.
The pristine form of graphene is not the most suitable for all conducting applications, however. For example, pure graphene sheet resistance is much higher than that of indium tin oxide (ITO) for similar levels of light transmission, meaning that ITO is the superior material for use in optoelectronics. The problem with ITO is its mechanical rigidity, which prevents its use in flexible devices.
Craciun and her team discovered an alternative to ITO in their investigation of FeCl3-intercalated few-layer graphene, which they named GraphExeter. Not only is this novel material flexible, but it matches ITO for transparency while exhibiting a lower sheet resistance and a higher work function, making it a good replacement for OLED and photovoltaic devices.
The researchers were able to grow large-area GraphExeter films by CVD on various substrates, and they found the material to be surprisingly robust. GraphExeter’s electrical properties were retained after a month-long exposure to 100% humidity, and remained constant even when it was heated in air to over 120º C. The material displayed impressive mechanical resilience, too, with the performance of a GraphExeter-based luminescent device unaffected by repeated strains of up to 1.8. These qualities mean that GraphExeter has great promise for use in external conductive coatings and flexible electronics – after all, who wants a wearable device that’s dry-clean only?
As with the fluorinated graphene, localized alteration of GraphExeter to plain graphene allowed Craciun team to inscribe useful structures that exploited the contrast in conductivity. By using a laser to selectively remove some of the intercalated molecules of FeCl3, the researchers produced photosensitive junctions with a size limited only by the laser diffraction limit. The resulting high-resolution photodetectors have a linear response over a huge range of energies, promising applications in high-energy environments.
As well as continuing their research on functionalized graphene, the group is currently studying other atomically thin materials such as dichalcogenides like molybdenum and tungsten disulphide. By combining 2D materials with organic layers, the group aims to create new substances and devices with unique electronic and optoelectronic properties not available in other systems.
Planned applications for the group current work include emerging technologies such as electronic textiles, smart windows (comprising displays integrated into the windscreens of vehicles), and a new generation of highly efficient solar cells and light-emitting devices.
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