Pascal Ruffieux

Affiliation: Swiss Federal Laboratories for Materials Science and Technology

Research Interests: nanographene, graphene nanoribbon, surface science
Title: On-surface synthesis of magnetic nanographenes
Abstract: Recent progress in the on-surface synthesis of nanographenes has given access to an extremely rich materials class where physical properties can be tuned in a wide range. The most prominent nanographenes include armchair graphene nanoribbons (GNRs) with width-dependent electronic band gaps [1], zigzag GNRs with spin-polarized edge states [2] and width-modulated GNRs hosting tunable topological bands [3]. Most recently, the successful synthesis of a series of open-shell nanographenes with magnetically nontrivial ground states has catapulted carbon-based magnetism to a new level. The basic concept followed here is realization of sublattice-imbalanced or topologically frustrated nanographenes hosting unpaired electrons. A deterministic realization of such nanographenes is achieved through a combined solution on and on-surface synthesis approach. Here, I will report recent advances in the on-surfaces synthesis of nanographenes with chemically tuned magnetic interaction strength between unpaired electrons in diradical nanographenes [4]. The controlled combination of different magnetic nanographenes allows formation of both, antiferromagnetically and ferromagnetically coupled dimers and trimers based on spin-½ and spin-1 molecular building blocks as well as extended spin chains [5]. Here, we investigate the length and site-dependent spin excitations with inelastic scanning tunneling spectroscopy and compare them theoretical predictions on spin-1 chains and confirm Haldane gap and fractional edge excitations for open chains. As an extension of the on-surface synthesis approach, we recently achieved successful formation of open-shell nanographenes using scanning tunneling microscopy tip-based activation of hydrogen-protected precursors [6,7]. This has the advantage that magnetic nanographenes can be prepared and characterized on a larger range of substrates since no specific catalytic substrate properties are needed here.