ON-SURFACE POLYMERIZATION ONTO A RARE-EARTH SURFACE-ALLOY

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A team of researchers Centro de Física de Materiales (CSIC-UPV/EHU) and Donostia International Physics Center (DIPC), San Sebastián have demonstrated that it is possible to realize atomically-organized organic nanostructures on a magnetic substrate of a reare-earth surface alloy without altering the magnetic properties of the substrate. The results, published in the journal ACS Nano, demonstrate that by clever engineering of the magnetic substrate it is possible to attain on-surface synthesis of tailored organic nanostructures thus opening the possibilities to study and control the magnetic properties of carbon-based magnetic nanostructures such as graphene nanoribbons.

Cerdanyola del Vallès, 13th February 2018.  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, oligonuclear spin-chains, and metal–organic networks. The ability to study such in situ synthesized structures, which offer an atomic precision of the product with control even over the edge topology, under precisely controlled experimental conditions and in direct contact with a ferromagnetic substrate is of fundamental interest, as it is envisioned as a promising route for studying the many phenomena of emergent carbon-based spintronics by means of spin-resolved measurement techniques offering submolecular spatial resolution.

In this work, published in the journal ACS Nano, researchers from the Centro de Física de Materiales (CSIC-UPV/EHU), ALBA Synchrotron and Donostia International Physics Center (DIPC) from the group of Enrique Ortega, demonstrate the on-surface polymerization of 4,4″-dibromo-p-terphenyl precursors into ordered poly(p-phenylene) arrays on top of the surface-alloy GdAu2 (Fig 1). The on-surface reaction is studied employing a multi-technique approach to investigate the chemical, electronic and structural properties of the molecular layer. The activation temperatures for bromine scission and subsequent homocoupling of molecular precursors were followed by temperature-dependent X-ray photoelectron spectroscopy. The structural characterizations of supramolecular and polymeric phases performed by low-energy electron diffraction and scanning tunneling microscopy, establish an extraordinary degree of order extending into the mesoscale. The transition of localized molecular orbitals into a highly dispersive π-band, the fingerprint of successful polymerization, was observed via angular resolved photoemission while leaving all surface-related bands intact. Moreover, employing X-ray magnetic circular dichroism measurements performed at BOREAS beamline (Fig.2) it was possible to demonstrate that although the on-surface reaction alters the magnetic properties of the GdAu2 surface alloy it does not destroy the magnetic order, thus opening the possibility to study carbon-based magnetic nanostructures with atomically-tailored structural properties such as graphene nanoribbons.

IM-BOREASH1

Figure 1: Low energy electron diffraction (LEED) patterns, scanning tunneling microscopy (STM) topography and structural model of the a) clean surface GdAu2 alloy, b) as-deposited 4,4″-dibromo-p-terphenyl precursors and c) polymerized poly(p-phenylene) molecular nanowires.

IM-BOREASH2

Figure 2: Magnetic characterization performed at BOREAS beamline, a) magnetization loops collected on the as-deposited 4,4″-dibromo-p-terphenyl precursors and polymerized poly(p-phenylene) layer, b) Arrot plots built out of the loops collected on the 4,4″-dibromo-p-terphenyl precursors layer and c) on the poly(p-phenylene) nano-chains.


The authors acknowledge funding from the Spanish MINECO under contract Nos. MAT2013-46593-C6-4-P and MAT2016-78293-C6-5-R as well as the Basque Government Grants IT621-13 and IT-756-13. J.B. and M.I. are grateful for insightful discussions with Frederik Schiller.

 

Reference: Polymerization of Well-Aligned Organic Nanowires on a Ferromagnetic Rare-Earth Surface Alloy. Mikel Abadía, Maxim Ilyn, Ignacio Piquero-Zulaica, Pierluigi Gargiani, Celia Rogero, José Enrique Ortega, and Jens Brede. ACS Nano 2017 11 (12), 12392-12401. DOI: 10.1021/acsnano.7b06374.

 

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