We aim at understanding the assembly of organic layers in dielectric surfaces and the structure on new metal-organic networks of variable dimensionality.
Among all metal oxides, TiO2 is considered as the model one for surface science experiments, since good quality surface terminations can be easily obtained. Additionally, it has acquired technological importance due to its performance in gas sensing, anti-corrosion coatings, photochemistry or heterogeneous catalysis. Actually, some of the results summarized below are part of the PhD thesis of Carlos Sánchez.
Reactivity of the TiO2 (110) surface towards organic molecules
We have been also devoted to investigate in a preliminary way the adsorption of organic molecules on the 1×1 reconstruction of TiO2 (110). In this case, we performed a collaboration with Dr. L. Floreano’s group, and we obtained some results on pentacene, C60, PTCDI, C60H30 and perilene molecules on this material.
Pentacene C60 PTCDI C60H30 Perilene
Some articles: Planar growth of pentacene on the dieletric TiO2(110) surface»,V. Lanzilotto, C. Sánchez-Sánchez, G. Bavdek, D. Cvetko, M. F. López, J. A. Martín-Gago, L. Floreano, « J. Phys. Chem. C, 115 (2011) 4664.
STM experimental image of pentacene molecules deposited on the TiO2(110) surface.
- * C. Sanchez-Sanchez, V. Lanzilotto, C. Gonzalez, A. Verdini, P. de Andrés, L. Floreano, M. F. López, J. A. Martín-Gago, “Weakly interacting molecular layer of spinning C60 molecules on TiO2 (110) surfaces”, Chem.-Eur. J., 18 (2012) 7382.
STM image of the two ccoexistent C60 phases identified on the TiO2(110)-(1×1) surface
Antiphase Boundaries Accumulation Forming a New C60 Decoupled Crystallographic Phase on the Rutile TiO2(110)-(1×1) Surface» C. Sánchez-Sánchez, J. I. Martínez, V. Lanzilotto, J. Méndez, J. A. Martín-Gago y M. F. López, «, J. Phys. Chem. C, 118, 27318 (2014),
* “Commensurate Growth of Densely Packed PTCDI Islands on the Rutile TiO2(110) Surface” V. Lanzilotto, G. Lovat, G. Otero, L. Sanchez, M. F. López, J. Méndez, J. A. Martín-Gago, G. Bavdek, L. Floreano, J. Phys, Chem. C, 117 (2013) 12639.
STM experimental image of a (1×5) PTCDI molecules island (left panel) and the geometrical model of the (1×5) PTCDI phase on the TiO2(110)-(1×1) surface (right panel) .
Chemistry and Temperature-assisted Dehydrogenation of C60H30 Molecules on Ti02(110) surfaces», C. Sánchez-Sánchez, J. I. Martínez, V. Lanzilotto, G. Biddau, B. Gómez-Lor, R. Pérez, L. Floreano, M. F. López, J. A. Martín-Gago, «Nanoscale, 5 (2013) 11058.
Figure: Upper panels show the representation of a C60H30 molecule before and after annealing at 750K. Lower panels exhibit the ball-and-stick schematic representation of the SACDH process operating during the molecular transformation.
«Densely Packed Perylene Layers on the Rutile TiO2(110)-(1 × 1) Surface», G. Otero-Irureta, J. I. Martínez, G. Lovat, V. Lanzilotto, J. Mendez, M. F. López, L. Floreano y J. A. Martin-Gago, J. Phys. Chem. C 119, 7809 (2015).
High coverage of perylene molecules on the TiO2(110) surface. In this case side-to-side molecular attraction sets in, which is shown to be mediated by a lateral intermolecular hybridization.
Studying the TiO2(110) surface reconstruction
In the last years, the study of the TiO2(110) surface, both with the 1×1 and the 1×2 surface reconstructions, has been a main research line in our scientific group. Firstly, we have determined the influence of the chemical and morphological tip conditions on STM images of TiO2(110).
Figure: Model for the TiO2(110)-(1×1) surface showing two typical types of defects: oxygen vacancies and OH.
Different ending tip settings were used to theoretically simulate the images for the well-known 1×1 TiO2(110) surface reconstruction. Hence, a comparison with the experimental STM images was performed. Additionally, the incorporation of O vacancies as well as OH groups as typical defects for this surface has been also investigated. The standard image without and with defects was properly reproduced by both a W tip and a W with O apex tip.
- * C. Sánchez-Sánchez, C. González, P. Jelinek, J. Méndez, P. L. de Andrés, J. A. Martín-Gago, M. F. López, «Understanding atomic-resolved STM images on TiO2(110)-(1×1) surface by DFT», Nanotechnology, 21 (2010) 405702.
The (1×2)-TiO2(110) surface reconstruction
In the case of the least studied reconstruction of the TiO2(110) surface, the 1×2, in the last years various proposals on the gemetrical disposition of the surface atoms have emerged mainly based on STM images. In this sense, we have been able to deduce the best model for the 1×2 surface reconstruction, which is based not only on STM work, but using a combination of STM, LEED-IV and ab-initio theoretical calculations.
- * M. Blanco-Rey, J. Abad, C. Rogero, J. Méndez, M. F. López, J. A. Martín-Gago, P. L. de Andrés, “Structure of Rutile TiO2 (110)-1×2: Formation of Ti2O3 Quasi-1D Metallic Chains”, Phys. Rev. Lett., 96 (2006) 055502.
- * M. Blanco-Rey, J. Abad, C. Rogero, J. Méndez, M. F. López, E. Román, J. A. Martín-Gago, P. L. de Andrés, “LEED-IV study of the rutile TiO2 (110)-1×2 surface with a Ti-interstitial added-row reconstruction”, Phys. Rev. B, 75 (2007) 081402(R).
After the determination of the 1×2 surface structure of TiO2(110), we have investigated its electronic structure. We have found that the defect-related state, located in the band gap, presents a double contribution, one associated to the surface Ti2O3 rows of the (1×2) reconstruction, and another related to the bulk defects.
- * C. Sánchez-Sánchez, M. G. Garnier, P. Aebi, M. Blanco-Rey, P. L. De Andrés, J. A. Martin-Gago, M. F. López, «Valence band electronic structure characterization of the rutile TiO2 (110)-(1×2) reconstructed surface», Surface Science, 608 (2013) 92.
Figure: UPS spectra of the band-gap states region for: (a) poorly reduced substrate with a (1×1) surface, (b) highly reduced substrate with (1×1) symmetry at the surface, (c) heavily reduced substrate with a (1×2) symmetry at the surface.
Additionally, the modifications originated in the surface properties by Pt deposition in a subnanometric regime, have been also determined as well as the evolution as a function of temperature
- * C. Sánchez-Sánchez, J. A. Martin-Gago, M. F. López, «Small Pt nanoparticles on the TiO2 (110) – (1×2) surface», Surface Science, 607 (2013) 159.
Figure: STM image of the TiO2(110)-(1×2) surface with a 0.1 ML Pt coverage after annealing at 825 K
The influence of oxygen adsorption on the 1×2 surface reconstruction was also a matter of our study.
- * J. Abad, C. Sánchez-Sánchez, P. Vilmercati, A. Goldoni, M. F. López, J. A. Martín-Gago, «Thermal behaviour of the O2/TiO2 (110)-(1×2) surface», Vacuum, 85 (2011) 1056.
Some other previous publications on TiO2(110):
- * J. Abad, C. Rogero, J. Méndez, M. F. López, J. A. Martín-Gago, E. Román, “Growth of subnanometer-thin Si overlayer on TiO2(110)-(1×2) surface”, Appl. Surf.Sci., 234 (2004) 497.
- * J. Abad, C. Rogero, J. Méndez, M. F. López, J. A. Martín-Gago, E. Román, “Ultra-thin Si overlayers on the TiO2(110)-(1×2) surface: growth mode and electronic properties”, Surf.Sci., 600 (2006) 2696.