On-surface metal-organic nanoporous networks generally refer to adatom coordinated molecular arrays, which are characterized by the presence of well-defined and regular nanopores. These periodic ...structures constructed using two types of components confine the surface electrons of the substrate within their nanocavities. However, the confining (or scattering) strength that individual building units exhibit is a priori unknown. Here, we study the modification of the substrate's surface electrons by the interaction with a Cu-coordinated TPyB metal-organic network formed on Cu(111) and disentangle the scattering potentials and confinement properties. By means of STM and angle-resolved photoemission spectroscopy we find almost unperturbed free-electron-like states stemming from the rather weak electron confinement that yields significant coupling between adjacent pores. Electron plane wave expansion simulations match the superlattice induced experimental electronic structure, which features replicating bands and energy renormalization effects. Notably, the electrostatic potential landscape obtained from our ab initio calculations suggests that the molecules are the dominant scattering entities while the coordination metal atoms sandwiched between them act as leaky channels. These metal atom transmission conduits facilitate and enhance the coupling among quantum dots, which are prone to be exploited to engineer the electronic structure of surface electron gases.
Vicinal surfaces exhibiting arrays of atomic steps are frequently investigated due to their diverse physical-chemical properties and their use as growth templates. However, surfaces featuring steps ...with a large number of low-coordinated kink-atoms have been widely ignored, despite their higher potential for chemistry and catalysis. Here, the equilibrium structure and the electronic states of vicinal Ag(111) surfaces with densely kinked steps are investigated in a systematic way using a curved crystal. With scanning tunneling microscopy we observe an exceptional structural homogeneity of this class of vicinals, reflected in the smooth probability distribution of terrace sizes at all vicinal angles. This allows us to observe, first, a subtle evolution of the terrace-size distribution as a function of the terrace-width that challenges statistical models of step lattices, and second, lattice fluctuations around resonant modes of surface states. As shown in angle resolved photoemission experiments, surface states undergo stronger scattering by fully-kinked step-edges, which triggers the full depletion of the two-dimensional band at surfaces with relatively small vicinal angles.
Quantum dot arrays in the form of molecular nanoporous networks are renowned for modifying the electronic surface properties through quantum confinement. Here we show that, compared to the pristine ...surface state, the band bottom of the confined states can exhibit downward shifts accompanied by a lowering of the effective masses simultaneous to the appearance of tiny gaps at the Brillouin zone boundaries. We observed these effects by angle resolved photoemission for two self-assembled homothetic (scalable) Co-coordinated metal-organic networks. Complementary scanning tunneling spectroscopy measurements confirmed these findings. Electron plane wave expansion simulations and density functional theory calculations provide insight into the nature of this phenomenon, which we assign to metal-organic overlayer-substrate interactions in the form of adatom-substrate hybridization. To date, the absence of the experimental band structure resulting from single metal adatom coordinated nanoporous networks has precluded the observation of the significant surface state renormalization reported here, which we infer to be general for low interacting and well-defined adatom arrays.
The importance of coffee cultivation in Nariño is reflected in the fact that 64% of its municipalities grow coffee. The ruggedness of its Andean topography provides great diversity in terms of ...climatic conditions, which, in one way or another, affect the behavior of coffee in all its physiological processes. Therefore, this study sought to identify the variation in the growth processes and production processes in the different coffee areas of this department, including the coffee-growing municipalities Sandoná, Consacá, La Florida and La Unión in the Department of Nariño, using experimental lots located at different altitude ranges (B <1600msnm; M between 1600 and 1800msnm and A >1800msnm). The statistical design used for each municipality was Random Complete Blocks with three treatments and sixteen repetitions. The recorded climatic variables included photosynthetically active radiation, ambient temperature, precipitation and relative humidity, and the evaluated physiological variables were plant height, number of leaves, basal stem diameter, number of primary branches, number of secondary branches, length of primary branches, number of knots per branch and leaf area index. The variable plant height was statistically higher in the upper zone (A) in the municipalities La Florida (79.95 cm) and Consacá (64.31cm); in La Florida, the number of branches and the LAI were higher in the upper zone plants, while the diameter of the stems was higher in the middle zone. In the other municipalities, these variables were not affected by the altitude.
The properties of crystalline solids can to a large extent be derived from the scale and dimensionality of periodic arrays of coupled quantum systems such as atoms and molecules. Periodic quantum ...confinement in two dimensions has been elusive on surfaces, mainly because of the challenge to produce regular nanopatterned structures that can trap electronic states. We report that the two-dimensional free electron gas of the Cu(111) surface state can be trapped within the pores of an organic nanoporous network, which can be regarded as a regular array of quantum dots. Moreover, a shallow dispersive electronic band structure is formed, which is indicative of electronic coupling between neighboring pore states.
The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in ...predefined ways through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to date through top-down methods, is preserved by the self-assembly process. This new strategy’s proof-of-concept compares experiments using 4,4′′-dibromo-para-terphenyl as a molecular precursor on flat Au(111) and stepped Au(322) substrates. As opposed to the former, the periodic steps of the latter drive the selective synthesis of 6 atom-wide armchair GNRs, whose electronic properties have been further characterized in detail by scanning tunneling spectroscopy, angle resolved photoemission, and density functional theory calculations.
The electronic character of a π-conjugated molecular overlayer on a metal surface can change from semiconducting to metallic, depending on how molecular orbitals arrange with respect to the ...electrode’s Fermi level. Molecular level alignment is thus a key property that strongly influences the performance of organic-based devices. In this work, we report how the electronic level alignment of copper phthalocyanines on metal surfaces can be tailored by controlling the substrate work function. We even show the way to finely tune it for one fixed phthalocyanine–metal combination without the need to intercalate substrate-functionalizing buffer layers. Instead, the work function is trimmed by appropriate design of the phthalocyanine’s supramolecular environment, such that charge transfer into empty molecular levels can be triggered across the metal–organic interface. These intriguing observations are the outcome of a powerful combination of surface-sensitive electron spectroscopies, which further reveal a number of characteristic spectroscopic fingerprints of a lifted LUMO degeneracy associated with the partial phthalocyanine charging.
A vicinal rutile TiO2(110) crystal with a smooth variation of atomic steps parallel to the 1–10 direction was analyzed locally with STM and ARPES. The step edge morphology changes across the samples, ...from 1–11 zigzag faceting to straight 1–10 steps. A step-bunching phase is attributed to an optimal (110) terrace width, where all bridge-bonded O atom vacancies (Obr vacs) vanish. The 1–10 steps terminate with a pair of 2-fold coordinated O atoms, which give rise to bright, triangular protrusions (St) in STM. The intensity of the Ti 3d-derived gap state correlates with the sum of Obr vacs plus St protrusions at steps, suggesting that both Obr vacs and steps contribute a similar effective charge to sample doping. The binding energy of the gap state shifts when going from the flat (110) surface toward densely stepped planes, pointing to differences in the Ti3+ polaron near steps and at terraces.
A quantum breadboard is presented on page 3757 by S. Nowakowska, L. H. Gade, J. Lobo‐Checa, T. A. Jung, and co‐workers, composed of a 2D metalorganic network creating surface state derived quantum ...well states in the pores. Scanning probe microscopy manipulation of Xe atoms is used to configure the Xe population of the pores, which affects the quantum state of the 2D array or breadboard.
Este artículo compara y contrasta distintas actitudes de Quevedo con respecto a la dimensión emocional de los seres humanos, concentrándose en varios poemas y en algunos tratados filosóficos y ...morales. El principal punto de referencia será la intensa y problemática relación del autor y el estoicismo clásico, en la que la admiración hacia figuras como Séneca y Epicteto debe coexistir con el rechazo agustiniano de la apatía estoica. Tal coexistencia produce evidentes tensiones en la obra de Quevedo, cuya defensa de la distancia y el autodominio afectivos entra en fricción con la exhortación a usar virtuosamente las emociones susceptibles de contribuir a nuestra salvación eterna. La poesía devocional de Quevedo va más allá de las perspectivas estoicas y neoestoicas sobre las emociones. Aquí Quevedo propone lo que podría calificarse como una inversión económica de las pasiones pecaminosas, con la esperanza de obtener sabiduría moral y arrepentimiento a través de la dolorosa experiencia del desengaño.
PDF
