Person: Díaz Blanco, Cristina
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First Name
Cristina
Last Name
Díaz Blanco
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Física
Area
Química Física
Identifiers
11 results
Search Results
Now showing 1 - 10 of 11
Item 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, FernandoThe 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.Item Optoelectronic properties of electronacceptor molecules adsorbed on graphene/silicon carbide interfaces(Communications materials, 2024) Mansouri, Masoud; Díaz Blanco, Cristina; Martín, Fernando; Springer NatureSilicon 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.Item 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, AlbaA 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.Item Efficient photogeneration of nonacene on nanostructured graphene(Nanoscale Horizons, 2021) Ayani, Cosme ; Pisarra, Michele; Urgel, José ; Navarro, Juan Jesús; Díaz Blanco, Cristina; Hayashi, Hironobu; Yamada, Hiroko; Calleja, Fabián; Miranda, Rodolfo; Fasel, Román; Martín, Fernando; Vázquez de Parga, AmadeoThe on-surface photogeneration of nonacene from a-bisdiketone precursors deposited on nanostructured epitaxial graphene grown on Ru(0001) has been studied by means of low temperature scanning tunneling microscopy and spectroscopy. The presence of an unoccupied surface state, spatially localized in the regions where the precursors are adsorbed, and energetically accessible in the region of the electromagnetic spectrum where n–p* transitions take place, allows for a 100% conversion of the precursors into nonacenes. With the help of state-of-the-art theoretical calculations, we show that such a high yield is due to the effective population of the surface state by the incoming light and the ensuing electron transfer to the unoccupied states of the precursors through an inelastic scattering mechanism. Our findings are the experimental confirmation that surface states can play a prominent role in the surface photochemistry of complex molecular systems, in accordance with early theoretical predictions made on small molecules.Item Accurate simulations of atomic diffractive scattering from KCl(0 0 1) under fast grazing incidence conditions(Nuclear Instruments and Methods in Physics Research B, 2020) Cueto, Marcos del; Muzas, Alberto; Martín, Fernando; Díaz Blanco, CristinaMotivated by recent experimental and theoretical results, we have studied the diffraction of atoms (D, 3He, 4He) from KCl(001). To perform this study, we have computed continuos potential energy surfaces (PESs) using density functional theory to obtain total interaction energies, with and without taking into account van der Waals forces, and the corrugation reduction procedure. Subsequently, we have performed quantum dynamics simulations using the multi-configuration time-dependent Hartree method. Our simulated spectra compare rather well with those recorded experimentally, specially well for 3He. The agreement is, in general, better for incidence along the [100] direction. In the case of He projectiles, the inclusion of vdW forces does not systematically improve agreement with the experiment. Finally, in agreement with similar calculations for other systems, we have found that the diffraction spectra are quite sensitive to the subtle characteristics of PES, whereas phonons and electronic excitations seem to play a minor role.Item 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, CristinaIn 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.Item Stereodynamics effects in grazing-incidence fast-molecule diffraction(Physical Chemistry Chemical Physics, 2022) del Cueto, Marco; Muzas, Alberto; Martín, Fernando; Díaz Blanco, CristinaGrazing-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.Item 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, TeresaThe 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.Item A simple model to engineer single-molecule conductance of acenes by chemical disubstitution(Nanoscale, 2022) Fallaque, Joel ; Rodríguez-González, Sandra; Díaz Blanco, Cristina; Martín, FernandoUnderstanding 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.Item Defect formation in a graphene overlayer on ruthenium under high pressure(Physical Review B, 2020) Pisarra, Michele; Díaz Blanco, Cristina; Martín, FernandoDue 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.