On-surface synthesis can be used to prepare one- or two-dimensional nanostructures via the coupling of organic building blocks. The monomeric coupling partners are deposited on, e.g., a metal surface and then coupled by thermal annealing. However, the coupling reaction competes with the desorption of the monomers. This especially limits reactions on inert graphite surfaces, while chemically active metal surfaces fare comparatively better. In an ultrahigh-vacuum environment, desorption is particularly dominant, which is why some on-surface syntheses are performed under ambient atmosphere. However, under these conditions, the resulting covalent nanostructures can degrade via hydrolysis in some cases.

Markus Lackinger, Technical University of Munich (TUM), Garching, Germany, and colleagues have found that thermal annealing under a noble gas atmosphere instead of in a vacuum kinetically inhibits desorption, allowing coupling reactions even on inert surfaces. In particular, the team performed a coupling reaction of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) via thioether bonds under an argon atmosphere (ca. 1 bar; reactions under vacuum and under Ar pictured schematically).

The researchers found that the reaction gave the desired fractal-like covalent network from the monomers, which have a three-fold symmetry, on graphite as well as on an even more weakly interacting graphene layer. According to the team, the work represents the first on-surface synthesis on inert graphene.

The team thinks the method might also be suitable for the transfer of other on-surface synthesis coupling reactions from chemically active metal surfaces to inert surfaces. In addition, the synthesis of covalent nanostructures on graphene could lead to potentially useful new materials.

• Noble Gas Provides a Solution to the Synthesis‐on‐Inert‐Surfaces Challenge for Extended Covalent Nanostructures,
  Lukas Grossmann, Sascha Korn, Rochus Breuer, Michael Schmittel, Heiko B. Weber, Wolfgang M. Heckl, Markus Lackinger,
  Angew. Chem. Int. Ed. 2025.
  https://doi.org/10.1002/anie.202422521