A central question in the field of graphene-related research is how graphenebehaves when it is patterned at the nanometer scale with different edgegeometries. Perhaps the most fundamental shape relevant to this question is thegraphene nanoribbon (GNR), a narrow strip of graphene that can have differentchirality depending on the angle at which it is cut. Such GNRs have beenpredicted to exhibit a wide range of behaviour (depending on their chiralityand width) that includes tunable energy gaps and the presence of uniqueone-dimensional (1D) edge states with unusual magnetic structure. Most GNRsexplored experimentally up to now have been characterized via electricalconductivity, leaving the critical relationship between electronic structureand local atomic geometry unclear (especially at edges). Here we present asub-nm-resolved scanning tunnelling microscopy (STM) and spectroscopy (STS)study of GNRs that allows us to examine how GNR electronic structure depends onthe chirality of atomically well-defined GNR edges. The GNRs used here werechemically synthesized via carbon nanotube (CNT) unzipping methods that allowflexible variation of GNR width, length, chirality, and substrate. Our STSmeasurements reveal the presence of 1D GNR edge states whose spatialcharacteristics closely match theoretical expectations for GNR's of similarwidth and chirality. We observe width-dependent splitting in the GNR edge stateenergy bands, providing compelling evidence of their magnetic nature. Theseresults confirm the novel electronic behaviour predicted for GNRs withatomically clean edges, and thus open the door to a whole new area ofapplications exploiting the unique magnetoelectronic properties of chiral GNRs.
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