Surface chemical reactions at epitaxial graphene and materials “beyond graphene”

  • Dipartimento di Fisica - Aula 500
  • Seminario

Relatori

A. Politano
University of Calabria, Department of Physics

Dettagli

Graphene (Gr) is a promising material in the fields of energy and catalysis. By means of a combination of surface-science spectroscopies and theory [1], we have investigated the mechanisms ruling the catalytic role of epitaxial Gr grown on transition-metal substrates for the production of hydrogen from water. Water decomposition at the Gr/metal interface at room temperature provides a hydrogenated Gr sheet, which is buckled and decoupled from the metal substrate. We have evaluated the performance of Gr/metal interface as a hydrogen storage medium, with a storage density in the Gr sheet comparable with state-of-the-art materials (1.42 wt.%). It is expected that decoration of Gr by Ca or transition-metal atoms and, moreover, the substitutional doping of Gr by N or B could further increase the gravimetric capacity. Moreover, thermal programmed reaction experiments show that molecular hydrogen can be released upon heating the water-exposed Gr/metal interface above 400 K. The Gr hydro/dehydrogenation process might be exploited for an effective and eco-friendly device to produce (and store) hydrogen from water, i.e. starting from an almost unlimited source. The role of defects in the intercalation and decomposition processes will be discussed.

The chemical reactivity of surface defects is also important for the prospect of electronic devices with active channels of ultrathin flakes of black phosphorus (few-layer phosphorene) [2, 3] or InSe [4], which require the use of capping layers.

Many studies have reported the oxidation of black phosphorus and the formation of P2O5 upon air exposure. However, the reactivity of phosphorene toward CO has been not studied yet. By means of vibrational spectroscopy and density functional theory, we have investigated CO adsorption on phosphorene-based systems. We find stable CO adsorption at room temperature on both phosphorene and bulk black phosphorus. The adsorption energy and the vibrational spectrum have been calculated for several possible configurations of the CO overlayer. The vibrational spectrum is characterized by two different C-O stretching energies. In particular, we find an unusual C-O vibrational band at 165-180 meV, activated by the lateral interactions in the CO overlayer on phosphorene-based systems.

Finally, the chemical inertness of high-quality single crystals of topological insulators toward ambient gases [5] will be discussed. The subsequent ambient stability of uncapped topological insulator-based nanodevices [6] paves the way for the technological exploitation of topological insulators. 

 

References

[1]          A. Politano, M. Cattelan, D. W. Boukhvalov, D. Campi, A. Cupolillo, S. Agnoli, N. G. Apostol, P. Lacovig, S. Lizzit, D. Farías, G. Chiarello, G. Granozzi and R. Larciprete, Unveiling the Mechanisms Leading to H2 Production Promoted by Water Decomposition on Epitaxial Graphene at Room Temperature, ACS Nano (2016) doi:10.1021/acsnano.6b00554.

[2]          L. Viti, J. Hu, D. Coquillat, W. Knap, A. Tredicucci, A. Politano and M. S. Vitiello, Black Phosphorus Terahertz Photodetectors, Adv. Mater. 27 (2015) 5567.

[3]          L. Viti, J. Hu, D. Coquillat, A. Politano, W. Knap and M. S. Vitiello, Efficient Terahertz detection in black-phosphorus nano-transistors with selective and controllable plasma-wave, bolometric and thermoelectric response, Sci. Rep. 6 (2016) 20474.

[4]          A. Politano, G. Chiarello, R. Samnakay, G. Liu, B. Gurbulak, S. Duman, A. A. Balandin and D. W. Boukhvalov, The influence of chemical reactivity of surface defects on ambient-stable InSe-based nanodevices, Nanoscale (2016) doi:10.1039/C6NR01262K.

[5]          A. Politano, M. Caputo, S. Nappini, F. Bondino, E. Magnano, Z. S. Aliev, M. B. Babanly, A. Goldoni, G. Chiarello and E. V. Chulkov, Exploring the Surface Chemical Reactivity of Single Crystals of Binary and Ternary Bismuth Chalcogenides, J. Phys. Chem. C 118 (2014) 21517.

[6] L. Viti, D. Coquillat, A. Politano, K. A. Kokh, Z. S. Aliev, M. B. Babanly, O. E. Tereshchenko, W. Knap, E. V. Chulkov and M. S. Vitiello, Plasma-Wave Terahertz Detection Mediated by Topological Insulators Surface States, Nano Lett. 16 (2016) 80.