Near edge X-ray absorption, valence and core-level photoemission, and density functional theory calculations are used to study molecular levels of tetracyano-2,3,5,6-tetrafluoroquinodimethane ...(F4TCNQ) deposited on Ag(111) and BiAg2/Ag(111). The high electron affinity of F4TCNQ triggers a large static charge transfer from the substrate, and, more interestingly, hybridization with the substrate leads to a radical change of symmetry, shape, and energy of frontier molecular orbitals. The lowest unoccupied molecular orbital (LUMO) shifts below the Fermi energy, becoming the new highest occupied molecular orbital (n-HOMO), whereas the n-LUMO is defined by a hybrid band with mixed π* and σ* symmetries, localized at quinone rings and cyano groups, respectively. The presence of Bi influences the way the molecule contacts the substrate with the cyano group. The molecule/surface distance is closer and the bond more extended over substrate atoms in F4TCNQ/Ag(111), whereas in F4TCNQ/BiAg2/Ag(111) the distance is larger and the contact more localized on top of Bi. This does not significantly alter molecular levels, but it causes the respective absence or presence of optical excitations in F4TCNQ core-level spectra.
Determining the scattering potential landscape for two-dimensional superlattices provides key insight into fundamental quantum electron phenomena. Theoretical and semiempirical methods have been ...extensively used to simulate confinement effects of the two-dimensional electron gas (2DEG) on superlattices with a single scatterer in the form of vicinal surfaces and dislocation networks or isolated structures such as quantum corrals and vacancy islands. However, the complexity of the problem increases when the building blocks (or scatterers) are heterogeneous, as in metal-organic nanoporous networks (MONNs), since additional potentials may come into play. Therefore, the parametrization of the surface potential landscape is often inaccurate, leading to incorrect scattering potentials. Here, we address this issue with a combination of scanning tunneling microscopy/spectroscopy, angle resolved photoemission spectroscopy and Kelvin probe force microscopy measurements together with electron plane-wave expansion simulations on a MONN grown on Cu(111). This experimental-theory approach, enables us to capture the 2DEG response to the intricate scattering potential landscape, and reveals systematic modeling procedures. Starting from a realistic geometry of the system, we determine the repulsive scattering potentials for both molecules and coordinated metal adatoms, the latter contradicting the established simulation framework. Moreover, we reveal local asymmetries and subtle renormalization effects of the 2DEG that relate to the interaction of the MONN and the underlying substrate.
Además de celebrar un acontecimiento bélico, en El asalto a Mastrique, Lope de Vega exalta la guerra como actividad que promueve sentimientos de cohesión nacionalista, fomentando entre los ...combatientes españoles formas de relación próximas a lo que el antropólogo Victor Turner denomina communitas. Mediante el estudio de varios aspectos (la comparación de la comedia con su fuente principal, la interacción en diversos planos de "lo alto" con "lo bajo", la caracterización heroica de Alejandro Farnesio), mi trabajo explora cómo Lope ve en esta communitas militar una imagen de las virtudes presuntamente anejas a la nación española. In addition to commemorating a historical ephemerides, Lope de Vega's El asalto de Mastrique exalts war as an activity that promotes feelings of national cohesion and fosters among soldiers something close to what the anthropologist Victor Turner calls communitas. In my article I study several aspects of this comedia-Lope's debts with his main source; the interaction at various levels of "high" and "low" elements; Alejandro Farnesio heroic characterization. My main goal is to explore how Lope sees in the military communitas depicted in the play an image of the alleged virtues of the Spanish nation.
A novel approach of identifying metal atoms within a metal-organic surface coordination network using scanning tunnelling microscopy (STM) is presented. The Cu adatoms coordinated in the porous ...surface network of 1,3,8,10-tetraazaperopyrene (TAPP) molecules on a Cu(111) surface give rise to a characteristic electronic resonance in STM experiments. Using density functional theory calculations, we provide strong evidence that this resonance is a fingerprint of the interaction between the molecules and the Cu adatoms. We also show that the bonding of the Cu adatoms to the organic exodentate ligands is characterised by both the mixing of the nitrogen lone-pair orbitals of TAPP with states on the Cu adatoms and the partial filling of the lowest unoccupied molecular orbital (LUMO) of the TAPP molecule. Furthermore, the key interactions determining the surface unit cell of the network are discussed.
We present a combined theoretical and experimental study revealing an STM fingerprint of the presence of the adatoms in a metal-organic coordination network.
La irrupción de lo monstruoso en los Sueños de Quevedo y en El Criticón de Gracián afecta según los casos a la conformación de los textos satíricos, a su reescritura no mimética del mundo cotidiano o ...la invención de imágenes inarmónicas y horribles. Este ensayo compara los distintos significados de lo monstruoso en uno y otro autor. Mientras para Quevedo dicha categoría problematiza la identidad semántica de los textos y repercute en su recepción ambivalente, Gracián procura contener la proliferación de su escritura cifrando en la imagen monstruosa varios principios constructivos y hermenéuticos del modo de representación alegórico.
En la Vida de Marco Bruto, Quevedo establece continuamente relaciones de afinidad o contrariedad entre los personajes representados en el texto, trasladando al estudio de la historia el principio de ...correspondencia característico de la poética conceptista. El propio método seguido por el autor cuestiona la posibilidad de obtener un conocimiento práctico y efectivo del mundo histórico, y pone de manifiesto que la noción de ejemplaridad ha entrado en crisis.
The photoemission cross-section of the Shockley surface state of Au(111) is studied over a wide range of photon energies both experimentally and theoretically. The measurements are fully understood ...based on the theoretical analysis within a one-step ab initio theory of photoemission. The constant initial state spectrum is shown to be very sensitive to the structure of the topmost atomic layer. A maximum in the constant initial spectrum at 60 eV is identified as a fingerprint of the Au(111) surface reconstruction.
The fields of organic electronics and spintronics have the potential to revolutionize the electronics industry. Finding the right materials that can retain their electrical and spin properties when ...combined is a technological and fundamental challenge. We carry out the study of three archetypal organic molecules in intimate contact with the BiAg2 surface alloy. We show that the BiAg2 alloy is an especially suited substrate due to its inertness as support for molecular films, exhibiting an almost complete absence of substrate-molecular interactions. This is inferred from the persistence of a completely unaltered giant spin-orbit split surface state of the BiAg2 substrate, and from the absence of significant metallic screening of charged molecular levels in the organic layer. Spin-orbit split states in BiAg2 turn out to be far more robust to organic overlayers than previously thought.
The bottom-up synthesis of carbon-based nanomaterials directly on semiconductor surfaces allows for the decoupling of their electronic and magnetic properties from the substrates. However, the ...typically reduced reactivity of such nonmetallic surfaces adversely affects the course of these reactions. Here, we achieve a high polymerization yield of halogenated polyphenyl molecular building blocks on the semiconducting TiO2(110) surface via concomitant surface decoration with cobalt atoms, which catalyze the Ullmann coupling reaction. Specifically, cobalt atoms trigger the debromination of 4,4″-dibromo-p-terphenyl molecules on TiO2(110) and mediate the formation of an intermediate organometallic phase already at room temperature (RT). As the debromination temperature is drastically reduced, homocoupling and polymerization readily proceed, preventing presursor desorption from the substrate and entailing a drastic increase of the poly-para-phenylene polymerization yield. The general efficacy of this mechanism is shown with an iodinated terphenyl derivative, which exhibits similar dehalogenation and reaction yield.
The development of chiral materials is severely limited by the challenge to achieve enantiopure derivatives with both configurational stability and good optoelectronic properties. Herein we ...demonstrate that enantiopure subphthalocyanines (SubPcs) fulfill such demanding requirements and bear the prospect of becoming components of chiral technologies. Particularly, we describe the synthesis of enantiopure SubPcs and assess the impact of chirality on aspects as fundamental as the supramolecular organization, the behavior in contact with metallic surfaces, and the on-surface reactivity and polymerization. We find that enantiopure SubPcs remarkably tend to organize in columnar polar assemblies at the solid state and highly ordered chiral superstructures on Au(111) surfaces. At the metal interface, such SubPcs are singled out by scanning tunneling microscopy. DFT calculations suggest that SubPcs undergo a bowl-to-bowl inversion that was shown to be dependent on the axial substituent. Finally, we polymerize by means of on-surface synthesis a highly regular 2D, porous and chiral, π-extended polymer that paves the way to future nanodevice fabrication.
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