Staff directory

Gustavo Ceballos Mago

Head of Scienctific Technical support Divisions
gustavo.ceballos(ELIMINAR)@icn2.cat
Scientific-Technical Research Support

Publications

2017

  • Symmetry forbidden morphologies and domain boundaries in nanoscale graphene islands

    Parreiras S.O., Gastaldo M., Moreno C., Martins M.D., Garcia-Lekue A., Ceballos G., Paniago R., Mugarza A. 2D Materials; 4 (2, 025104) 2017. 10.1088/2053-1583/aa70fa. IF: 6.937

    The synthesis of graphene nanoislands with tailored quantum properties requires an atomic control of the morphology and crystal structure. As one reduces their size down to the nanometer scale, domain boundary and edge energetics, as well as nucleation and growth mechanisms impose different stability and kinetic landscape from that at the microscale. This offers the possibility to synthesize structures that are exclusive to the nanoscale, but also calls for fundamental growth studies in order to control them. By employing high-resolution scanning tunneling microscopy we elucidate the atomic stacking configurations, domain boundaries, and edge structure of graphene nanoislands grown on Ni(1 1 1) by CVD and post-annealed at different temperatures. We find a non-conventional multistep mechanism that separates the thermal regimes for growth, edge reconstruction, and final stacking configuration, leading to nanoisland morphologies that are incompatible with their stacking symmetry. Whole islands shift their stacking configuration during cooling down, and others present continuous transitions at the edges. A statistical analysis of the domain structures obtained at different annealing temperatures reveals how polycrystalline, ill-defined structures heal into shape-selected islands of a single predominant stacking. The high crystallinity and the control on morphology and edge structure makes these graphene nanoislands ideal for their application in optoelectronics and spintronics. © 2017 IOP Publishing Ltd.


2015

  • Substrate-induced stabilization and reconstruction of zigzag edges in graphene nanoislands on Ni(111)

    Garcia-Lekue A., Olle M., Sanchez-Portal D., Palacios J.J., Mugarza A., Ceballos G., Gambardella P. Journal of Physical Chemistry C; 119 (8): 4072 - 4078. 2015. 10.1021/jp511069y. IF: 4.772

    We combine experimental observations by scanning tunneling microscopy (STM) and density functional theory (DFT) to reveal the most stable edge structures of graphene on Ni(111) as well as the role of stacking-driven activation and suppression of edge reconstruction. Depending on the position of the outermost carbon atoms relative to hollow and on-top Ni sites, zigzag edges have very different energies. Triangular graphene nanoislands are exclusively bound by the more stable zigzag hollow edges. In hexagonal nanoislands, which are constrained by geometry to alternate zigzag hollow and zigzag top edges along their perimeter, only the hollow edge is stable, whereas the top edges spontaneously reconstruct into the (57) pentagon-heptagon structure. Atomically resolved STM images are consistent with either top-fcc or top-hcp epitaxial stacking of graphene and Ni sites, with the former being favored by DFT. Finally, we find that there is a one-to-one relationship between the edge type, graphene stacking, and orientation of the graphene islands. © 2015 American Chemical Society.


2014

  • Atomic monolayer deposition on the surface of nanotube mechanical resonators

    Tavernarakis, A.; Chaste, J.; Eichler, A.; Ceballos, G.; Gordillo, M.C.; Boronat, J.; Bachtold, A. Physical Review Letters; 2014. 10.1103/PhysRevLett.112.196103. IF: 7.728


  • Spin tuning of electron-doped metal-phthalocyanine layers

    Stepanow, S.; Lodi Rizzini, A.; Krull, C.; Kavich, J.; Cezar, J.C.; Yakhou-Harris, F.; Sheverdyaeva, P.M.; Moras, P.; Carbone, C.; Ceballos, G.; Mugarza, A.; Gambardella, P. Journal of the American Chemical Society; 136 (14): 5451 - 5459. 2014. 10.1021/ja501204q. IF: 11.444


  • Spin-dependent electron scattering at graphene edges on Ni(111)

    Garcia-Lekue, A.; Balashov, T.; Olle, M.; Ceballos, G.; Arnau, A.; Gambardella, P.; Sanchez-Portal, D.; Mugarza, A. Physical Review Letters; 2014. 10.1103/PhysRevLett.112.066802. IF: 7.728


2012

  • A nanomechanical mass sensor with yoctogram resolution

    Chastem J. ; Eichler, A.; Moser, J.; Ceballos, G.; Rurali, R.; Bachtold, A. Nature Nanotechnology; 7: 301 - 304. 2012. .


  • Yield and Shape Selection of Graphene Nanoislands Grown on Ni(111)

    Olle, M. ; Ceballos, G.; Serrate, D.; Gambardella, P. Nano Letters; 12(9): 4431 - 4436. 2012. DOI: 10.1021/nl300897m.


2011

  • Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100)

    Stepanow, S.; Mugarza, A.; Ceballos, G.; Gambardella, P.; Aldazabal, I.; Borisov, A.G.; Arnau, A. Physical Review B - Condensed Matter and Materials Physics; 83 2011. 10.1103/PhysRevB.83.115101.


  • Mixed-valence behavior and strong correlation effects of metal phthalocyanines adsorbed on metals

    Stepanow, S.; Miedema, P. S.; Mugarza, A.; Ceballos, G. ; Moras, P. ; Cezar, J. C.; Carbone, C. ; de Groot, F. M. F.; Gambardella, P. Physical Review B; 2011. .


  • Spin coupling and relaxation inside molecule-metal contacts.

    Mugarza, A.; Krull, C.; Robles, R.; Stepanow, S.; Ceballos, G.; Gambardella, P. Nature Communications; 2 2011. 10.1038/ncomms1497.


2010

  • Giant spin and orbital moment anisotropies of a Cu-phthalocyanine monolayer

    Stepanow, S.; Mugarza, A.; Ceballos, G.; Moras, P.; Cezar, J.C.; Carbone, C.; Gambardella, P. Physical Review B - Condensed Matter and Materials Physics; 82 2010. 10.1103/PhysRevB.82.014405.


  • Orbital specific chirality and homochiral self-assembly of achiral molecules induced by charge transfer and spontaneous symmetry breaking

    Mugarza A., Lorente N., Ordejón P., Krull C., Stepanow S., Bocquet M.-L., Fraxedas J., Ceballos G., Gambardella P. Physical Review Letters; 105 (11, 115702) 2010. 10.1103/PhysRevLett.105.115702.

    We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers. © 2010 The American Physical Society.


2007

  • Insulating ground state of Sn/Si(111)-(¿30 x¿30)R30°

    S. Modesti; L. Petaccia; G. Ceballos; I. Vobornik; G. Panaccione; G. Rossi; L. Ottaviano; R. Larciprete; S. Lizzit; A. Goldoni Physical Review Letters; 2007. .


  • Role of the electric field in surface electron dynamics above the vacuum level

    J. I. Pascual; C. Corriol; G. Ceballos; I. Aldazabal; H.-P. Rust; K. Horn; J. M. Pitarke; P. M. Echenique; A. Arnau Physical Review B; 2007. .