Silicon has dominated solid-state electronics for more than four decades but now a variety of other materials are being explored in photonic devices to expand the wavelength range of operation and to improve performance. Graphene is such a material - although most research on graphene so far has focused mainly on electronics. IBM researchers have now shown that graphene-based devices can be used in optical communications. Introducing this new material system into photonics could have a significant impact on mainstream optical applications. By using graphene, researchers make use of the internal electric field that exists at the interface of graphene and metal. Through a sophisticated combination of palladium and titanium electrodes they created a photodetector that does not rely on external current.
Carbon-supported catalysts are widely used in many applications. For example, platinum nanoparticles supported on bulk carbon frameworks are used as fuel cell electrodes. The obvious challenge is to have a large area of carbon surface so that the catalyst particles can be dispersed without any aggregation. Graphene with its 2D nanostructure provides a large surface area (theoretically, the surface area of graphene is about 2600 square meters per gram) to anchor catalyst particles. Scientists have now succeeded in dispersing two different types of nanoparticles - silver and titanium dioxide - on a reduced graphene oxide at different sites without any aggregation.
A group of researchers from Singapore, led by Professor Dingyuan Tang from Nanyang Technological University and Professor Kian Ping Loh from National University of Singapore, have reported the first breakthrough in using few-layer graphene as a saturable absorber for the mode locking of lasers. Despite its prominent mechanical and electrical properties, graphene's optical response has previously been considered to be weak and featureless, so the main interests of the research community are centered on its electronics properties. But now, Tang and Loh demonstrate that graphene can be used for telecommunications applications and that its weak and universal optical response might be turned into advantages for ultrafast photonics applications.
Graphene based sheets such as pristine graphene, graphene oxide, or reduced graphene oxide are basically single atomic layers of carbon network. They are the world's thinnest materials. A general visualization method that allows quick observation of these sheets would be highly desirable as it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies. Current imaging techniques for observing graphene based sheets include atomic force microscopy, transmission electron microscopy, scanning electron microscopy and optical microscopy. Some of these techniques are rather low-throughput. And all the current techniques require the use of special types of substrates. This greatly limits the capability to study these materials. Researchers from Northwestern University have now reported a new method, namely fluorescence quenching microscopy, for visualizing graphene-based sheets.
Chip structures already have reached nanoscale dimensions but as they continue to shrink below the 20 nanometer mark, ever more complex challenges arise and scaling appears not to be economically feasible any more. And below 10 nm, the fundamental physical limits of CMOS technology will be reached.
One promising material that could enable the chip industry to move beyond the current CMOS technology is graphene, a monolayer sheet of carbon. Notwithstanding the intense research interest, large scale production of single layer graphene remains a significant challenge. Researchers at Cornell University have now reported a new technique for producing large scale single layer graphene sheets and fabricating transistor arrays with uniform electrical properties directly on the device substrate.
Graphene is an impressive condensed matter system that, to all appearances, never ceases to impress and challenge our entrenched intuitions regarding solid state systems. But graphene is a highly atypical electronic system in that it consists of nothing but a surface. Researchers at Boston University have found that local deformations in a graphene sheet can strongly influence electron flow across the system, causing suppression of conductance at low densities, and making electrons behave as if they were living in a nanoribbon or quantum dot. All this without cutting the graphene sheet, which opens the prospect towards a reversible and controllable transport gap in monolayer graphene via strain engineering.
Nanostructures present novel material properties and interesting insight into new physical phenomena. However, from a technical and commercial application point of view, a successful bridging between the nanoscale specific significance with large-scale applications must be made to obtain these benefits. One of the 'hottest' nanomaterials at the moment is graphene, a one-atom thick sheet of carbon. Ribbons made from graphene, basically stripes that look like molecular chicken wire, show even more unconventional properties than graphene, especially when they are less than 100 nm wide. Any material approach to use graphene nanoribbons for larger-scale applications must be able to assemble them into macroscopic materials, while preserving their physical significance and novel properties at these larger scales. Researchers at MIT have addressed this issue by proposing hierarchical assemblies of graphene nanoribbons through hydrogen bonds, inspired by biological structures found in nature such as proteins and DNA macromolecules.
The most promising applications of graphene are in electronics, detectors, and thermal management. The first graphene field-effect transistors have already been demonstrated. At the same time, for any transistor to be useful for analog communication or digital applications, the level of the electronic low-frequency noise has to be decreased to an acceptable level. Low frequency electronic noise dominates the noise spectrum to a frequency of about 100 kHz. Despite the fact that modern electronic devices such as cell phones and radars operate at a much higher carrier frequency, the low frequency noise is extremely important. Due to unavoidable non-linearities in devices and systems, the low frequency noise gets up-converted, and contributes to the phase noise of the system, thus limiting its performance. It is not possible to build a communication system or detector based on graphene devices until the noise spectral density is decreased to the level comparable with the conventional state-of-the-art transistors. Researchers at the University of California - Riverside have now reported the results of experimental investigation of the low-frequency noise in a double-gate graphene transistors.