Organics on oxide surfaces

 

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.

 

Sin título

              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.

Fig2

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.

ptcdi-TiO2

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).

 

perileno-tio2

 

 

 

 

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.

Figure: a) STM experimental image of the TiO2(110)-(1×1) surface. A double tip formed by two O atoms adsorbed at the apex is the responsible of the image, as inferred from theoretical calculations (image b). The presence of defects has also been simulated theoretically (images c and d).

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.

Figure: Ti2O3 model for the TiO2(110)-1×2 surface

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.

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

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.

 Some other previous publications on TiO2(110):

 

 

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