SCIENTIFIC HIGHLIGHTS

Improving the stability of the electrode-molecule interface

In this work, we show that Au−C bond can provide a robust and well-defined anchoring geometry for single molecule junctions

The molecule/electrode contact plays a fundamental role in the performance of molecular electronic devices since it directly affects the charge transport across the interface. The search for a more stable molecule−electrode bond, a well-defined interface geometry, and more conductive interfaces is the driving force to pursue robust and efficient molecule based devices. Interestingly, some recent works have shown that the formation of covalent highly directional σ-bonded C−Au junctions provides high conductance at the single-molecule level. In this field, we are very much interested in exploring organic paramagnetic and electroactive molecules which are attracting interest as core components of molecular electronic and spintronic devices. In this work, we reported the synthesis of a persistent organic radical bearing one and two terminal alkyne groups to spontaneously form Au−C σ bonds. On the one hand, the formation and stability of self-assembled monolayers was achieved and, the electron transport through the SAMs and single-molecule junctions at room temperature was studied. We first demonstrated that the magnetic character is preserved after covalent bonding. Strikingly, it was shown that the investigated system allows for drastic improvements in the reproducibility of single molecule conductance measurements and bond strength when compared to other commonly used contacts such as S-Au. Through a detailed comparison with a similar thiophene functionalized derivative, we proved that the Au−C bond provides a more robust and better-defined anchoring geometry as supported by DFT calculations. Our findings open the door to more reproducible spintronics devices based on multifunctional molecules.

Authors:
Francesc Bejarano,1 Ignacio Jose Olavarria-Contreras,2 Andrea Droghetti,3 Ivan Rungger,4 Alexander Rudnev,5,6 Diego Gutierrez,1 Marta Mas-Torrent,1 Jaume Veciana,1 Herre S. J. van der Zant,2 Concepció Rovira,1 Enrique Burzurı,́2,7 and Núria Crivillers1

Affiliation of the authors:
1Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB- CSIC) and CIBER-BBN, Spain  
2Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands
3Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Universidad del País Vasco (UPV/EHU), Spain
4 National Physical Laboratory, United Kingdom
5Department of Chemistry and Biochemistry, University of Bern, Switzerland
6Russian Academy of Sciences A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Russia
7IMDEA Nanoscience, Spain

Publication:
Robust Organic Radical Molecular Junctions Using Acetylene Terminated Groups for C-Au Bond Formation
Am. Chem. Soc. 140, 5, 1691-1696 (2018)
DOI: 10.1021/jacs.7b10019

Figure caption
A 2D conductance vs electrode displacement histogram of the radical molecule constructed from 2500 consecutive traces at RT and 0.2 V bias voltage. The inset shows some selected individual traces. B Scheme of the SAM (top) and MCBJ (bottom) based on the novel organic radical.

 

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