Person:
Díaz Blanco, Cristina

First Name

Cristina

Last Name

Díaz Blanco

URI

https://hdl.handle.net/20.500.14352/76092

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Químicas

Department

Química Física

Area

Química Física

Identifiers

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Now showing 1 - 10 of 13

Graphene grown on transition metal substrates: Versatile templates for organic molecules with new properties and structures
(Surface Science Reports, 2022) Díaz Blanco, Cristina; Calleja, Fabián; Vázquez de Parga, Amadeo L.; Martín, Fernando
The interest in graphene (a carbon monolayer) adsorbed on metal surfaces goes back to the 60’s, long before isolated graphene was produced in the laboratory. Owing to the carbon-metal interaction and the lattice mismatch between the carbon monolayer and the metal surface, graphene usually adopts a rippled structure, known as moir´e, that confers it interesting electronic properties not present in isolated graphene. These moir´e structures can be used as versatile templates where to adsorb, isolate and assemble organic-molecule structures with some desired geometric and electronic properties. In this review, we first describe the main experimental techniques and the theoretical methods currently available to produce and characterize these complex systems. Then, we review the diversity of moir´e structures that have been reported in the literature and the consequences for the electronic properties of graphene, attending to the magnitude of the lattice mismatch and the type of interaction, chemical or physical, between graphene and the metal surface. Subsequently, we address the problem of the adsorption of single organic molecules and then of several ones, from dimers to complete monolayers, describing both the different arrangements that these molecules can adopt as well as their physical and chemical properties. We pay a special attention to graphene/Ru(0001) due to its exceptional electronic properties, which have been used to induce long-range magnetic order in tetracyanoquinodimethane (TCNQ) monolayers, to catalyze the (reversible) reaction between acetonitrile and TCNQ molecules and to efficiently photogenerate large acenes.
Optoelectronic properties of electronacceptor molecules adsorbed on graphene/silicon carbide interfaces
(Communications materials, 2024) Mansouri, Masoud; Díaz Blanco, Cristina; Martín, Fernando; Springer Nature
Silicon carbide has emerged as an optimal semiconducting support for graphene growth. In previous studies, the formation of an interfacial graphene-like buffer layer covalently bonded to silicon carbide has been observed, revealing electronic properties distinct from ideal graphene. Despite extensive experimental efforts dedicated to this interface, theoretical investigations have been confined to its ground state. Here, we use many-body perturbation theory to study the electronic and optical characteristics of this interface and demonstrate its potential for optoelectronics. By adsorbing graphene, we show that the quasiparticle band structure exhibits a reduced bandgap, associated with an optical onset in the visible energy window. Furthermore, we reveal that the absorption of two prototypical electron-accepting molecules on this substrate results in a significant renormalization of the adsorbate gap, giving rise to distinct low-lying optically excited states in the near-infrared region. These states are well-separated from the substrate’s absorption bands, ensuring wavelength selectivity for molecular optoelectronic applications.
Engineering the HOMO–LUMO gap of indeno[1,2b]fluorene
(Journal of Materials Chemistry C, 2022) Casares, Raquel; Martínez-Pinel, Álvaro; Rodríguez-González, Sandra; Márquez, Irene ; Lezama, Luis; González, Maria Teresa; Leary, Edmund; Blanco, Víctor; Fallaque, Joel ; Díaz Blanco, Cristina; Martín, Fernando; Cuerva, Juan ; Millán, Alba
A direct, efficient and versatile strategy for the modulation of optoelectronic and magnetic properties of indeno[1,2-b]fluorene has been developed. 4-Substituted-2,6-dimethylphenyl acetylene groups placed in the apical carbon of the five-membered rings lead to redshifted absorption maxima (lmax rangin from 600–700 nm) and considerable narrowing of the HOMO–LUMO energy gap (down to 1.5 eV). Experimental and theoretical data show an increase in the diradical character (y) and a decrease of the singlet-triplet energy gap. Moreover, we have investigated the single-molecule conductance of the antiaromatic indeno[1,2-b]fluorene for the first time by including thiomethyl (-SMe) anchor groups on the phenylacetylene moiety. Conductance values one order of magnitude higher than those of a reference linear 3-ring para-phenylene ethylene have been found, despite the longer length of the S-to-S molecular junction. First principles transport calculations support this high conductance value.
Evaluation of the role of graphene-based Cu(I) catalysts in borylation reactions
(Catalysis Science & Technology, 2021) Franco, Mario; Sainz, Raquel; Lamsabhi, Al Mokhtar; Díaz Blanco, Cristina; Tortosa, Mariola; Cid, M. Belén
Carbon-supported catalysts have been considered as macromolecular ligands which modulate the activity of the metallic catalytic center. Understanding the properties and the factors that control the interactions between the metal and support allows a fine tuning of the catalyzed processes. Although huge effort has been devoted to comprehending binding energies and charge transfer for single atom noble metals, the interaction of graphenic surfaces with cheap and versatile Cu(I) salts has been scarcely studied. A methodical experimental and theoretical analysis of different carbon-based Cu(I) materials in the context of the development of an efficient, general, scalable, and sustainable borylation reaction of aliphatic and aromatic halides has been performed. We have also examined the effect of microwave (MW) radiation in the preparation of these type of materials using sustainable graphite nanoplatelets (GNP) as a support. A detailed analysis of all the possible species in solution revealed that the catalysis is mainly due to an interesting synergetic Cu2O/graphene performance, which has been corroborated by an extensive theoretical study. We demonstrated through DFT calculations at a high level of theory that graphene enhances the reactivity of the metal in Cu2O against the halide derivative favoring a radical departure from the halogen. Moreover, this material is able to stabilize radical intermediates providing unexpected pathways not observed using homogeneous Cu(I) catalysed reactions. Finally, we proved that other common carbon-based supports like carbon black, graphene oxide and reduced graphene oxide provided poorer results in the borylation process.
Self-energy corrected DFT-NEGF for conductance in molecular junctions: an accurate and efficient implementation for TRANSIESTA package applied to Au electrodes
(Journal of physics: Condensed Matter, 2022) Fallaque, Joel ; Rodríguez-González, Sandra; Martín, Fernando; Díaz Blanco, Cristina
In view of the development and the importance that the studies of conductance through molecular junctions is acquiring, robust, reliable and easy-to-use theoretical tools are the most required. Here, we present an efficient implementation of the self-energy correction to density functional theory non-equilibrium Green functions method for TRANSIESTA package. We have assessed the validity of our implementation using as benchmark systems a family of acene complexes with increasing number of aromatic rings and several anchoring groups. Our theoretical results show an excellent agreement with experimentally available measurements assuring the robustness and accuracy of our implementation.
Grazing incidence fast atom and molecule diffraction: theoretical challenges
(Physical Chemistry Chemical Physics, 2022) Díaz Blanco, Cristina; Gravielle, María Silvia
This perspective article reviews the state-of-the-art of grazing incidence fast atom and molecule diffraction (GIFAD and GIFMD) simulations and addresses the main challenges that theorists, aiming to provide useful inputs in this topic, are facing. We first discuss briefly the methods used to build accurate potential energy surfaces describing the interaction between the projectile and the surface. Subsequently, we focus on the dynamics simulation methods for GIFAD, a phenomenon that has received a lot of experimental attention since 2007, when the first measurements were published. Following this experimental effort, theorists have developed and adapted a bunch of methods able to simulate, analyze and extract information from the experimental outputs. We review these methods, from the very simple ones based on classical dynamics to the full quantum ones, paying special attention to more versatile semiclassical approaches, which include quantum ingredients in the dynamics at a computational cost only slightly higher than that required in classical dynamics. Within the semiclassical framework it is possible, for example, to include in the dynamics the surface phonons and the projectile coherence, two factors that may have a relevant influence on the experimental measurements, at a reasonable computational cost. Finally, we address GIFMD, a phenomenon that has received much less attention and for which there is still a lot of room for research. We review the few examples of GIFMD available in the literature, and we discuss new phenomena associated with the molecular internal degrees of freedom, which may have some impact in other closely related fields, such as molecular reactivity on metal surfaces. Finally, we point out opened questions, raised from the comparisons between theoretical and experimental results, which claim for further experimental efforts.
Stereodynamics effects in grazing-incidence fast-molecule diffraction
(Physical Chemistry Chemical Physics, 2022) del Cueto, Marco; Muzas, Alberto; Martín, Fernando; Díaz Blanco, Cristina
Grazing-incidence fast-projectile diffraction has been proposed both as a complement and an alternative to thermal-energy projectile scattering, which explains the interest that this technique has received in recent years, especially in the case of atomic projectiles. On the other hand, despite the richer physics involved, molecular projectiles have received much less attention. In this work, we present a theoretical study of grazing-incidence fast-molecule diffraction of H2 from KCl(001) using a sixdimensional density functional theory based potential energy surface and a time-dependent wavepacket propagation method. The analysis of the computed diffraction patterns as a function of the molecular alignment, and their comparison with the available experimental data, where the initial distribution of rotational states in the molecule is not known, reveals a puzzling stereodynamics effect of the diffracted projectiles: diffracted molecules aligned perpendicular, or quasi perpendicular, to the surface reproduce rather well the experimental diffraction pattern, whereas those molecules aligned parallel to or tilted with respect to the surface do not behave as in the experiments. These results call for more detailed investigations of the molecular beam generation process.
Single‐molecule conductance of 1,4‐azaborine derivatives as models of BN‐doped PAHs
(Angewandte Chemie International Edition, 2021) Palomino‐Ruiz, Lucía; Rodríguez‐González, Sandra; Fallaque, Joel ; Márquez, Irene ; Agraït, Nicolás; Díaz Blanco, Cristina; Leary, Edmund; Cuerva, Juan ; Campaña, Araceli ; Martín, Fernando; Millán, Alba; González, Teresa
The single‐molecule conductance of a series of BN‐acene‐like derivatives has been measured by using scanning tunneling break‐junction techniques. A strategic design of the target molecules has allowed us to include azaborine units in positions that unambiguously ensure electron transport through both heteroatoms, which is relevant for the development of customized BN‐doped nanographenes. We show that the conductance of the anthracene azaborine derivative is comparable to that of the pristine all‐carbon anthracene compound. Notably, this heteroatom substitution has also allowed us to perform similar measurements on the corresponding pentacene‐like compound, which is found to have a similar conductance, thus evidencing that B–N doping could also be used to stabilize and characterize larger acenes for molecular electronics applications. Our conclusions are supported by state‐of‐the‐art transport calculations.
A simple model to engineer single-molecule conductance of acenes by chemical disubstitution
(Nanoscale, 2022) Fallaque, Joel ; Rodríguez-González, Sandra; Díaz Blanco, Cristina; Martín, Fernando
Understanding and controlling electrical conductivity at the single-molecule level is of fundamental importance for the development of new molecular electronic devices. This ideally requires considering the many different options offered by the molecular structure, the nature of the electrodes, and all possible molecule-electrode anchoring configurations, which is experimentally tedious and theoretically very expensive. Here we present a systematic theoretical study of the conductance of di-amino, di-methylthio and di-(4-methylthio)phenyl acenes, from benzene to pentacene, and for all possible distributions of two identical linkers symmetrically placed on opposite sides of the same ring. We show that, for all investigated compounds, the relative variation of the conductance is well explained by the variations of the HOMO energies as predicted by a simple extended-Hückel approach, i.e., without the need for further input from more elaborate calculations. The model predicts quite nicely that diamino acenes are better conductors than their corresponding dimethylthio analogues, and both much better than the di-(4-methylthio)phenyl counterparts, irrespective of the linkers’ relative positions. It also predicts, for a given pair of linkers, the variations in the conductance resulting from changing the acene size and/or the relative position of the linkers. These variations can be as large as an order of magnitude, and therefore can be used to engineer molecular conductance. Finally, we show that a similar approach should be useful to predict trends in the relative conductance of a large variety of disubstituted acene isomers, including various linkers.
Defect formation in a graphene overlayer on ruthenium under high pressure
(Physical Review B, 2020) Pisarra, Michele; Díaz Blanco, Cristina; Martín, Fernando
Due to its highly corrugated moiré structure and the nanometer modulation of its electronic properties, graphene deposited on ruthenium substrates (G-Ru for short) is a versatile playground for molecular deposition and chemical reactivity. Under local ultrahigh pressure conditions, one can expect an even richer behavior, reinforced by the likely appearance of defects. We have theoretically investigated the formation of such defects on G-Ru by using density functional theory methods. We show that defects can be produced in the high areas of the moiré, either by generating reactive centers in graphene through the creation of vacancies or by modifying the relative carbon-ruthenium positions through conformational changes. The energetic cost to induce these defects is rather small, of the order of a few eV, so that defects are expected to appear when impacting a STM tip or applying high pressure by a diamond AFM tip in these regions. The different types of defects can be clearly distinguished from each other in our simulated STM images.