“We expect these porous, nitrogen-doped graphene ribbons to display extraordinary magnetic properties. In the future, the ribbons could therefore be of interest for applications in quantum computing.”Ernst Meyer
A team led by researchers from the University of Basel and the University of Bern have developed the first graphene nanoribbons where the crystal lattice contains both periodic pores and a regular pattern of nitrogen atoms. The material, doped with nitrogen, is structured as a ladder with rungs containing two atoms of nitrogen, and could lead to new technology in electronics and quantum computing.
As reported in the Journal of the American Chemical Society [Pawlak et al, J. Am. Chem. Soc. (2020) DOI: 10.1021/jacs.0c03946], to synthesize these porous, nitrogen-containing graphene ribbons, each building block was heated on a silver surface in a vacuum, with the ribbons being formed at temperatures reaching 220°C. Atomic force microscopy was used to assess each step in the synthesis, and to confirm both the ladder structure and stability of the molecule.
For a workable on/off ratio for switching, as in a transistor, graphene nanoribbons need a band gap, and the approach here was to combine nanoscale holes with nitrogen dopant atoms into the nanoribbons. Microscopy also showed that the nanoribbons were no longer electrical conductors, as in pure graphene, but behaved as semiconductors, which was confirmed by theoretical calculations. Cavities spaced every 0.84 nm in 1.2 nm wide nanoribbons were produced, which ensured an energy gap that was stable under thermal annealing conditions could be observed, a property that could find many uses in molecular electronics and optoelectronics. Combining both doping and porous structures helped tune the gap of the ribbons and could lead to materials with uncompensated spins.
Graphene has a range of unique properties, including electrical conductivity and excellent strength and rigidity, and many studies have explored these by substituting carbon atoms in the crystal lattice with atoms of different elements. The materials electric and magnetic properties can also be altered by the formation of pores in the lattice, with a high concentration of nitrogen atoms in the crystal lattice being known to result in graphene ribbons becoming magnetized when subjected to a magnetic field. As co-team leader Ernst Meyer said, “We expect these porous, nitrogen-doped graphene ribbons to display extraordinary magnetic properties. In the future, the ribbons could therefore be of interest for applications in quantum computing”.
The approach is a promising avenue for synthesis, and one that offers atomically clean material since within the ribbons there were no defects observed. In future research the team may investigate the most effective way to determine the magnetic properties of the nanoribbons, as well as potential quantum computation applications if spins are uncompensated.
Doped graphene nanoribbons in ladder-like structure