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Nanostructured graphene catalyzes the reaction between two organic molecules
Speaker Speaker: Dott. Michele Pisarra
Affiliato Affiliato: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nano), and Departamento de Química, Universidad Autónoma de Madrid, Campus de Cantoblanco, 24049, Madrid, Spain
Data Evento Giovedì 16 Maggio , alle ore 16.30 - Aula Seminari, Cubo 31C
The graphene-substrate interaction can be a powerful tool to tune the electronic properties of graphene [1]. A paradigmatic example is the graphene/Ru(0001) interface. The lattice mismatch between the two systems gives rise to a strong corrugation in graphene, dramatic variations of the graphene-metal interaction, and a strong modulation of the electronic properties at the nanometer scale [2]. Furthermore the graphene overlayer isolates efficiently any adsorbed molecules from the
highly reactive metal surface. This fact has been explored in the past, when the graphene/Ru(0001) interface has been used as an adsorption template for the TCNQ molecule, which, due to charge transfer, have an unpaired electron and hence behaves as a magnetic impurity, displaying the Kondo effect [3]. On the other hand, the CH2-CN· radical have also been employed to covalently pattern the graphene/Ru(0001) surface with high spatial selectivity [4]. In view of these results, a natural development is determining the role of supported graphene as a catalytic agent, studying the chemical reaction that may take place when multiple molecular species
are adsorbed on the nano-patterned graphene/Ru(0001) surface. In this talk I will present our recent results on this topic [5], analyzing the adsorption of a TCNQ molecule on a graphene/Ru(0001) surface, previously functionalized with (CH2-CN·) radicals. By means of Density Functional Theory (DFT) calculations we determined that the graphene/Ru(0001) surface promotes the formation of TCNQ-CH2CN, in which the two molecule are bonded by means of a C-C covalent bond, a reaction that would hardly take place under non catalyzed conditions. The new TCNQ-CH2CN molecule has no magnetic moment, due to charge transfer from the surface. More interestingly, the reaction can be fully reversed by injecting electrons in the LUMO of the molecule by the STM tip. The TCNQ-CH2CN/TCNQ duo can hence be used as a reversible magnetic switch, controlled by a chemical reaction. Finally we demonstrate that the observed phenomenon is more general, as a similar graphene catalyzed reaction takes place between the TCNQ molecule and Hydrogen atoms used to functionalize the graphene/Ru(0001) surface. In this respect our study shows that the TCNQ molecule can be used as a chemical “mop”, with which strongly bound addends can be removed from the graphene surface.

References
[1] J. Winterlin et al., Surf. Sci. 603, 1841 (2009)
[2] B. Borca et al., Phys. Rev. Lett. 105, 036804 (2010); D. Stradi et al., Phys. Rev. B 85,
121404(R) (2012)
[3] M. Garnica et al., Nature Phys. 9, 368 (2013); M. Garnica et al., NanoLett. 14, 4560 (2014);
[4] J. J. Navarro et al. Nano Lett. s16, 355 (2016); J. J. Navarro et al. Chem. Comm. 53, 10418
(2017).
[5] J. J. Navarro, M. Pisarra et al. Science Advances (2018) 4, eaau9366