Professor Seung-Hoon Jhi and Ph.D. Candidate Seon-Myeong Choi, both of the Department of Physics, in their study of metal doped graphene nanoribbons, discovered that the adsorbed metal atoms form atomic chains which can be used as reagents to identify the edge atomic structures of the graphene nanoribbons and also as gate-driven spin valves to control the spin current in graphene nanoribbons.

Graphene, the basic structural element of all graphitic materials including graphite, carbon nanotubes and fullerenes, is a one-atom-thick planar sheet of carbon atoms that are densely packed in a honeycomb crystal lattice. Placed in layers on top of each other, it would take 200,000 membranes to reach high enough to match the thickness of a human hair.

Graphene nanostructures have attracted great attention due to their unique and intriguing electronic and transport properties. Particularly, the graphene nanoribbons’ carrier mobility is very promising for high-speed electronic devices.

Professor Jhi’s team studied electronic and magnetic properties of alkali and alkaline-earth metal doped graphene nanoribbons by the pseudopotential density functional method. The findings are that strong site dependence is observed in metal adsorption on graphene nanoribbons, and that the adsorbed metal atoms are found to spontaneously form atomic chains at the edges of zigzag-edged graphene nanoribbons. The self-assembled atomic chains can be used to analyze the atomic structures of the graphene nanoribbon edges, which had proved difficult due to the extreme thinness of graphene.

Also, such doped graphene nanoribbons exhibited intriguing magnetic properties such as hysteresis and spin compensation as metal atoms switch from one edge to another at alternating gate voltages. Using this phenomenon, the research team suggested a schematic model for the spin-valve structure that drives alkali metal atoms from one edge of a zigzag-edged graphene nanoribbon to the other.

The research outcomes were presented in the December 31, 2008 issue of Physical Review Letters.