Coupled spin states in armchair graphene nanoribbons with asymmetric zigzag edge extensions

Carbon-based magnetic structures promise significantly longer coherence times than traditional magnetic materials, which is of fundamental importance for spintronic applications. An elegant way of achieving carbon-based magnetic moments is the design of graphene nanostructures with an imbalanced occupation of the two sublattices forming the carbon honeycomb lattice. According to Lieb's theorem, this induces local magnetic moments that are proportional to the sublattice imbalance. Exact positioning of sublattice imbalanced nanostructures in graphene nanomaterials hence offers a route to control interactions between induced local magnetic moments and to obtain graphene nanomaterials with magnetically non-trivial ground states. Here, we show that such sublattice imbalanced nanostructures can be incorporated along a large band gap armchair graphene nanoribbon on the basis of asymmetric zigzag edge extensions, which is achieved by incorporating specifically designed precursor monomers during the bottom-up fabrication of the graphene nanoribbons. Scanning tunneling spectroscopy of an isolated and electronically decoupled zigzag edge extension reveals Hubbard-split states in accordance with theoretical predictions. Investigation of pairs of such zigzag edge extensions reveals ferromagnetic, antiferromagnetic or quenching of the magnetic interactions depending on the relative alignment of the asymmetric edge extensions. Moreover, a ferromagnetic spin chain is demonstrated for a periodic pattern of zigzag edge extensions along the nanoribbon axis. This work opens a route towards the design and fabrication of graphene nanoribbon-based spin chains with complex magnetic ground states

Generation of nitrile groups on graphites in a nitrogen RF-plasma discharge

AbstractGraphite particles were treated in a nitrogen radio frequency-plasma (RF-plasma) at different excitation power. The morphological as well as chemical surface modifications were investigated by Raman spectroscopy, SEM, and XPS. Changes of the sp2/sp3 bonding ratio and selective surface terminations by functional groups were achieved. Especially, a direct functionalization of the graphites with nitrile groups was evidenced by a characteristic signal at 2240cm−1 in the Raman spectra after a high energy RF-nitrogen plasma treatment. A total nitrogen content of up to 11at.% was reached by the applied conditions. The increased polarity of the surfaces was confirmed by contact angle measurements. The nitrile functionalization may serve as synthetic scaffold for the development of new routes towards the chemical surface modification of carbon substrates. Furthermore, the modified graphites can be processed by common exfoliation techniques yielding nitrogen modified graphene nanoplatelets directly in polar and non-polar solvents

Raman spectroscopy of holey nanographene C216

We report a detailed investigation by Raman spectroscopy of the holey nanographene C216, a hexagon-shaped disk with armchair edges (1.4 nm long), from which the central aromatic ring is missing. Density functional theory (DFT) calculations allow to assign the main features of the Raman spectra that have been recorded with several excitation wavelengths. In the Raman spectra, we observe signatures of the hole in the structure, several G and D modes, as well as their overtones and combinations-up to third order