In order to use graphene for electronic components such as field effect transistors, the material has to be ‘transformed’ into a semiconductor. The scientists achieved this by growing the nanoribbons on a metal surface from specifically designed precursor molecules. They also ‘doped’ the nanoribbons by furnishing them with impurity atoms such as nitrogen at certain points, in order to further influence the electronic properties of the GNR.
The Empa team, led by Roman Fasel, says it synthesised GNR with perfectly zigzagged edges following a specific geometry along the longitudinal axis of the ribbons. According to the scientists, this is an important step, because it can give GNR different properties via the geometry of the ribbons and especially via the structure of their edges.
The special feature of the zigzag GNR is that, along each edge, the electrons all spin in the same direction; an effect which is referred to as ferromagnetic coupling. At the same time, the so-called antiferromagnetic coupling ensures that the electrons on the other edge all spin in the opposite direction.
Thus, two independent spin-channels with opposite directions of travel arise on the band edges. Via intentionally integrated structural defects on the edges or via the provision of an electrical, magnetic or optical signal from the outside, spin barriers and spin filters can be designed that require only energy in order to be switched on and off - the precursor to a nanoscale, extremely energy efficient transistor.
According to the researchers, these properties could make GNR suitable for use in spintronic devices, which use both the charge and the spin of the electrons. This combination is prompting scientists to forecast completely new components, such as addressable magnetic data storage devices which maintain the information that has been fed in even after the power has been turned off.
