PGI-1 Talk: Dr. Jens Brede

On-surface synthesis and magnetic characterization of graphene nanoribbons on top of a two-dimensional magnetic surface alloy

Materials Physics Center, San Sebastian

Abstract:

The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the realization of more sophisticated on-surface reactions, thereby depriving these interfaces of a significant class of chemically tailored organics such as graphene nanoribbons (GNRs), oligonuclear spin-chains, and metal−organic networks.
In the first part of this talk, I will present a multi-technique characterization of the polymerization of 4,4″-dibromo-p-terphenyl precursors into ordered poly(p-phenylene) arrays on top of an emerging class of two-dimensional magnetic surface alloys. The chemical reaction was followed by temperature-dependent X-ray photoelectron spectroscopy (XPS) and the structural characterizations of supramolecular and polymeric phases were performed by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Taking advantage of the high homogeneity of the samples, the electronic structure of the valence band was determined with angle-resolved photoemission spectroscopy (ARPES). Moreover, ferromagnetic ordering in the two-dimensional GdAu2 alloy was demonstrated for all phases by X-ray absorption spectroscopy (XAS).
In the second part, I will briefly show that GdAu2 is not only a suitable template for the surfaceconfined Ullmann-like coupling reaction but is also thermally sufficiently stable to sustain a cyclodehydrogenation reaction for the on-surface synthesis of more complex GNRs. Thus, the system is demonstrated to close a longstanding experimental gap in the study of GNRs as it enables spinpolarized STM characterizations of e.g. the spin-polarization of the elusive GNR edge-states, which were theoretically predicted for chiral GNRs and experimentally, albeit lacking spinsensitivity, observed on Au(111). However, successive theoretical studies questioned and refined, respectively, the experimental prerequisites under which magnetic ordering of edgestates in GNRs may be observed, thereby highlighting the need for direct experimental access of the spin-polarization of these states.

Kontakt

Stefan Blügel

Telefon: +49 2461 61-4249

Fax:  +49 2461 61-2850

E-Mail: s.bluegel@fz-juelich.de