Correct Answer: D
Explanation:
Researchers from the Indian Institute of Science (IISc), Bengaluru have been able to experimentally produce a new type of electrical conductor that was theoretically predicted nearly 20 years ago.
The team produced graphene that is single- or a few-layers thick to conduct current along one particular edge — the zigzag edge.
The zigzag edge of graphene layer has a unique property: It allows flow of charge without any resistance at room temperature and above.
This is the first time one has found the perfect edge structure in graphene and demonstrated electrical conductance along the edge.
A few-layers-thick graphene that conducts current along one edge does not experience any resistance and so can lead to realising power-efficient electronics and quantum information transfer, even at room temperature.
Many groups over the world have been trying to access these edges since the emergence of graphene in 2004, but have been largely unsuccessful because when current flows through graphene, it flows through both the edge as well as the bulk.
By creating the bulk part of graphene extremely narrow (less than 10 nanometre thick), and hence highly resistive, thus forcing the current to flow through the edge alone, IISc scientists have overcome this block.
While the bulk is totally insulating, the edge alone has the ability to conduct because of the unique quantum mechanics of the edge.
As the zigzag orientation of carbon atoms [resulting from the hexagonal lattice], the electron wave on each carbon atom overlaps and forms a continuous train of wave along the edge.
This makes the edge conducting, even if it is very long but has to be chemically and structurally pristine.
In the past, others researchers had tried making narrow graphene through chemical methods.
But the use of chemicals destroys the edges. So the IISc team resorted to mechanical exfoliation to make graphene that are single- and few-layers thick.
There are currently several chemical methods to produce very narrow graphene nanoribbons. But these chemicals tend to destroy the edges.
So the challenge is to produce graphene nanoribbons using chemicals that do not destroy the edges.
This innovation makes high-quality graphene nano-ribbons or nano-strips with clean edges possible.