DURING THE last three decades, significant research efforts have resulted in the size reduction of silicon-based semiconductor electronic devices in accordance with Moore's law.

Advances in microelectronic fabrication by lithography techniques have helped in miniaturazing electronic circuits at a fast rate for the past two decades.

Size reduction

But scientists and engineers predict that within the next decade the limit for the ultimate size reduction in silicon-based devices will be reached creating a dead end in the chip technology.

The need for developing a substitute material to silicon has been realized a decade ago. The advancements in nanoscience and technology have given hope for the development of molecular electronic devices with fast response for a technological revolution.

Graphene isolation

The research carried out in 2004 by Andre Geim and Kostya Novoselov at the Manchester University, United Kingdom on the isolation of graphene, a single layer of graphite, has stirred the excitement of scientific fraternity for its unusual properties.

The science of graphene is now a hot topic in physics and materials science. Graphene is the first isolated 2D nanomaterial.

Andre Geim prepared graphene layers by a procedure called micromechanical cleavage which can be accomplished by peeling the top layers of a highly oriented pyrolytic graphite with a scotch tape.

Raman spectroscopy can be used to identify the number of graphene sheets in the layer. The ele,,ctronic structure and electron-phonon interactions are different for single, bilayer or a few layer graphenes, approaching the 3D limit of graphite at 10 layers.

Monolayer sheets

The one atomic thick 2D graphene monolayer sheets are not only ultra-thin, but ultra-strong, can be made as highly-insulating or highly-conductive. Graphene is quite stable under ambient conditions.

The charge carriers in graphene are best described by massless Dirac fermions moving at very high speed comparable to that of light.

These quasi particles can be viewed as electrons that have lost their rest mass or as neutrinos that acquired the electronic charge.

Such massless charged particles have not been observed before. Graphene exhibits a pronounced ambipolar electric field effect at room temperature itself in that the charge carriers can be tuned continuously between electrons and holes in high concentrations and mobilities and physicists predict there is further scope to improve the mobility by appropriate doping procedures.

Another interesting experimental observation on graphene is the anomalous quantum Hall effect (QHE). QHE is usually observed at very low temperatures, typically below -243{+o} C.

The astonishing observation of QHE in graphene at room temperature in 2007 opens up new vistas for graphene-based resistance standards and quantum devices.

The Manchester group has already developed a graphene-based gas sensor and electronic devices. In March 2006, Professor Walt de Heer at the Georgia Institute of Technology in U.S. produced graphene-based transistors, loop devices and electronic circuitry.

Electronic systems

Graphene layers less than 10 atoms thick can form the basis for revolutionary electronic systems that would manipulate electrons as waves rather than particles, much like photonic systems control light waves.

The anticipation that graphene transistors will provide life to electronic devices after the death of silicon may not be an exaggeration after all.

R. SARASWATHI & C. SRINIVASAN

Department of Materials Science
Madurai Kamaraj University, Madurai

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