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Los nuevos escenarios que caracterizan al siglo XXI se ven reflejados en una extensión creciente de las responsabilidades legales aplicables a la industria inmobiliaria. Sin embargo, sus profesionales siguen confiando en el éxito histórico de sus habilidades técnicas, eludiendo el hecho que esta evolución de la sociedad obliga a considerar también el desafío de un mayor deber de cuidado. En este contexto, este documento presenta la visión personal de un ingeniero civil y aficionado a las leyes, respecto de algunos alcances de esta nueva cultura de judicialización.

Background and study aims The COVID-19 outbreak has reorganized surgical team conditions regarding endoscopy . The number of interventions has been reduced, the number of healthcare professionals must be limited, and both the patients and physicians are more protected than ever. Patients and Methods In the highest peak of contagion in Colombia, endoscopy, colonoscopy, and esophagogastroduodenoscopy were performed using a low-cost disposable device. A total of 1388 procedures were performed. Every patient was assessed for symptoms via a telephone call, at the health center, and after the procedure, following specific attention routes. Results After procedure follow-up, no positive cases of COVID-19 were noted. Conclusion The methodology reduced the risk of infection during the COVID-19 pandemic.

Electronic devices based on bidimensional materials (2DMs) are the subject of an intense experimental research, that demands a tantamount theoretical activity. The latter must be hold up by a varied set of tools able to rationalize, explain and predict the operation principles of the devices. However, in the broad context of multi-scale computational nanoelectronics, there is currently a lack of simulation tools connecting atomistic descriptions with semi-classical mesoscopic device-level simulations and able to properly explain the performance of many state-of-the-art devices. To contribute to filling this gap we present a multi-scale approach that combines fine-level material calculations with a semi-classical drift-diffusion transport model. Its use is exemplified by assessing 2DM field effect transistors with strained channels, showing excellent capabilities to capture the changes in the crystal structure and their impact into the device performance. Interestingly, we verify the capacity of strain in monolayer GaSe to enhance the conduction of one type of carrier, enabling the possibility to mimic the effect of chemical doping on 2D materials. These results illustrate the great potential of the proposed approach to bridge levels of abstraction rarely connected before and thus contribute to the theoretical modeling of state-of-the-art 2DM-based devices.

International audience; The West Indies are a natural laboratory for the study of biogeography and evolution, especially for mammals. The modality of their arrival in the Caribbean islands is a highly controversial issue, and palaeontological evidence remains particularly elusive. Lower Oligocene deposits of Puerto Rico (c. 29.5 Ma) have recently yielded the oldest archipelago rodents, with teeth of two chinchilloid caviomorphs of South American origin. Here we report the discovery of additional dental remains from the same level, testifying to the occurrence of another rodent group. Their morphology is singular but otherwise characteristic of North/Central American geomyin geomorphs (including extant kangaroo rats, pocket mice, and pocket gophers), and leads us to propose here a new taxon: Caribeomys merzeraudi gen. et sp. nov. The evidence of geomorphs in the West Indies challenges the view that all extinct and extant Antillean rodents derived from South American sources. The morphological singularity of this Puerto Rican geomorph also suggests an early split of this insular lineage from coeval mainland counterparts, and its dispersal towards the West Indies sometime around the Eocene–Oligocene transition. This unexpected rodent adds to the few cases of Antillean terrestrial vertebrates of North American origins, such as solenodonotan eulipotyphlans. In the absence of subaerial land connections between both landmasses, an overwater dispersal may explain mid-Palaeogene colonization of the West Indies by geomorph rodents.

We present a methodology to address, from first principles, charge-spin interconversion in two-dimensional materials with spin-orbit coupling. Our study relies on an implementation of density functional theory based quantum transport formalism adapted to such purpose. We show how an analysis of the $k$-resolved spin polarization gives the necessary insight to understand the different charge-spin interconversion mechanisms. We have tested it in the simplest scenario of isolated graphene in a perpendicular electric field where effective tight-binding models are available to compare with. Our results show that the flow of an unpolarized current across a single layer of graphene produces, as expected, a spin separation perpendicular to the current for two of the three spin components (out-of-plane and longitudinal), which is the signature of the spin Hall effect. Additionally, it also yields an overall spin accumulation for the third spin component (perpendicular to the current), which is the signature of the Rashba-Edelstein effect. Even in this simple example, our results reveal an unexpected competition between the Rashba and the intrinsic spin-orbit coupling. Remarkably, the sign of the accumulated spin density does not depend on the electron or hole nature of the injected current for realistic values of the Rashba coupling., Comment: 10 pages, 9 figures

By their past and present diversity, rodents are among the richest components of Caribbean land mammals. Many of these became extinct recently. Causes of their extirpation, their phylogenetic affinities, the timing of their arrival in the West Indies and their biogeographic history are all ongoing debated issues. Here, we report the discovery of dental remains from Lower Oligocene deposits (ca29.5 Ma) of Puerto Rico. Their morphology attests to the presence of two distinct species of chinchilloid caviomorphs, closely related to dinomyids in a phylogenetic analysis, and thus of undisputable South American origin. These fossils represent the earliest Caribbean rodents known thus far. They could extend back to 30 Ma the lineages of some recently extinct Caribbean giant rodents (ElasmodontomysandAmblyrhiza), which are also retrieved here as chinchilloids. This new find has substantial biogeographic implications because it demonstrates an early dispersal of land mammals from South America to the West Indies, perhaps via the emergence of the Aves Ridge that occurredca35–33 Ma (GAARlandia hypothesis). Considering both this new palaeontological evidence and recent molecular divergence estimates, the natural colonization of the West Indies by rodents probably occurred through multiple and time-staggered dispersal events (chinchilloids, then echimyid octodontoids (spiny rats/hutias), caviids and lastly oryzomyin muroids (rice rats)).

We investigate the production of spin-polarized currents in corrugated graphene nanoribbons. Such corrugations are modeled as multiple regions with Rashba spin-orbit interactions, where concave and convex curvatures are treated as Rashba regions with opposite signs. Numerical examples for different separated Rashba-zone geometries calculated within the tight-binding approximation are provided. Remarkably, the spin-polarized current in a system with several Rashba areas can be enhanced with respect to the case with a single Rashba part of the same total area. The enhancement is larger for configurations with multiple regions with the same Rashba sign. This indicates that the increase of the spin polarization is due to the scattering of the electrons traversing regions with and without Rashba interaction. Additionally, we relate the appearance of the spin-polarized currents to novel symmetry relations between the spin-dependent conductances. These symmetries turn out to be a combination of different symmetry operations in real and spin spaces, as those occurring in non-planar systems like carbon nanotubes. Our results show that two-dimensional devices with Rashba spin-orbit interaction can be used as excellent spintronic devices in an all-electrical or mechanical setup., 13 pages, 7 figures

Hexagonal boron nitride (hBN) is attracting a lot of attention in the last years, thanks to its many remarkable properties. These include the presence of single-photon emitters with superior optical properties, which make it an ideal candidate for a plethora of photonic technologies. However, despite the large number of experimental results and theoretical calculations, the structure of the defects responsible for the observed emission is still under debate. In this work, we visualize individual atomic-scale defects in hBN with atomic force microscopy under ambient conditions and observe multiple narrow emission lines from optically stable emitters. This direct observation of the structure of the defects combined with density functional theory calculations of their band structures and electronic properties allows us to associate the existence of several single-photon transitions to the observed defects. Our work sheds light on the origin of single-photon emission in hBN that is important for the understanding and tunability of high-quality emitters in optoelectronics and quantum technologies.

We explore deformations of finite chains of noninteracting fermions at half-filling which give rise to large correlations between their extremes. After a detailed study of the Su-Schrieffer-Heeger model, the tradeoff curve between end-to-end correlations and the energy gap of the chains is obtained using machine-learning techniques, paying special attention to the scaling behavior with the chain length. We find that edge-dimerized chains, where the second and penultimate hoppings are reinforced, are very often close to the optimal configurations. Our results allow us to conjecture that, given a fixed gap, the maximal attainable correlation falls exponentially with the system size. Study of the entanglement entropy and contour of the optimal configurations suggest that the bulk entanglement pattern is minimally modified from the clean case.

This article introduces and discusses the concept of entanglement detachment. Under some circumstances, enlarging a few couplings of a Hamiltonian can effectively detach a (possibly disjoint) block within the ground state. This detachment is characterized by a sharp decrease in the entanglement entropy between block and environment, and leads to an increase of the internal correlations between the (possibly distant) sites of the block. We provide some examples of this detachment in free fermionic systems. The first example is an edge-dimerized chain, where the second and penultimate hoppings are increased. In that case, the two extreme sites constitute a block which disentangles from the rest of the chain. Further examples are given by (a) a superlattice which can be detached from a 1D chain, and (b) a star-graph, where the extreme sites can be detached or not depending on the presence of an external magnetic field, in analogy with the Aharonov-Bohm effect. We characterize these detached blocks by their reduced matrices, specially through their entanglement spectrum and entanglement Hamiltonian.

87Sr/86Sr-derived mean ages from low-Mg calcite Kuphus incrassatus and Ostrea haitensis bivalves provide an updated and refined chronostratigraphy for selected Oligocene-Miocene carbonate and siliciclastic units in Puerto Rico and the Dominican Republic. Results indicate ages of middle to late Oligocene for the San Sebastian Formation (ca. 29.78–26.51 Ma), the Lares Limestone (ca. 26.51–24.73 Ma), and the Montebello Member (ca. 27.30–24.10 Ma); middle Miocene to the early part of the late Miocene for the Cibao Formation (ca. 12.17 Ma), the Aguada (Los Puertos) Limestone (ca. 14.67–11.14 Ma), and the Aymamon Limestone (ca. 10.98 Ma) in northern Puerto Rico as well as for the Ponce Limestone (ca. 14.97–9.84 Ma) in southern Puerto Rico and the Yanigua–Los Haitises Formations (ca. 15.75–12.58 Ma) in northeastern Dominican Republic; and late Miocene for the Cercado Formation (ca. 6.31–5.88 Ma) in northwestern Dominican Republic. These results show some significant modifications to previous chronostrati...

The production of spin-polarized currents in pristine carbon nanotubes with Rashba spin-orbit interactions has been shown to be very sensitive to the symmetry of the tubes and the geometry of the setup. Here we analyze the role of defects on the spin quantum conductances of metallic carbon nanotubes due to an external electric field. We show that localized defects, such as adsorbed hydrogen atoms or pentagon-heptagon pairs, increase the Rashba spin-polarized current. Moreover, this enhancement takes place for energies closer to the Fermi energy as compared to the response of pristine tubes. Such increments can be even larger when several equally spaced defects are introduced into the system. We explore different arrangements of defects, showing that for certain geometries there are flips of the spin-polarized current and even transport suppression. Our results indicate that spin valve devices at the nanoscale may be achieved via defect engineering in carbon nanotubes., A.L. acknowledges the financial support of FAPERJ through Grants No. E-26/102.272/2013 and No. E-26/202.953/2016, CNPq, and INCT em Nanomateriais de Carbono. L.C. acknowledges support from Spanish MINECO through Grant No. FIS2015-64654-P, and helpful conversations with Jorge I. Cerdá. H.S. is grateful for financial support from the Brazilian CAPES.

Graphene edges present localized electronic states strongly depending on their shape, size and border configuration. Chiral- or zigzag-ended graphene nanostructures develop spatially and spectrally localized edge states around the Fermi level; however, atomic scale investigations of such graphene terminations and their related electronic states are very challenging and many of their properties remain unexplored. Here we present a combined experimental and theoretical study on graphene stripes showing strong metallic edge states at room temperature. By means of scanning tunneling microscopy, we demonstrate the use of vicinal Pt(111) as a template for the growth of graphene stripes and characterize their electronic structure. We find the formation of a sublattice localized electronic state confined on the free-standing edges of the graphene ribbons at energies close to the Fermi level. These experimental results are reproduced and understood with tight-binding and ab initio calculations. Our results provide a new way of synthesizing wide graphene stripes with zigzag edge termination and open new prospects in the study of valley and spin phenomena at their interfaces., P. M. was supported by the “Rafael Calvo Rodés” Program. L. C. thanks the support of the Spanish MINECO through project FIS2015-64654-P. J. A. M.-G. acknowledges funding from the Spanish MINECO (Grant MAT2014-54231-C4-1-P) and the ERC-Synergy Program (Grant ERC-2013-SYG-610256 Nanocosmos). The research leading to these results has received funding from the European Union Seventh Framework Programme under Grant agreement No. 604391 Graphene Flagship. Open Access funding provided by the Max Planck Society.

The stratigraphic range of the Coalcomana–Caprinuloidea rudist assemblage from Puerto Rico, the Dominican Republic and Jamaica has been revised based on numerical ages derived from strontium isotope (87Sr/86Sr) analyses of the calcitic outer shell of requieniid rudists. The extent of diagenetic alteration was assessed by cathodoluminescence microscopy and trace element concentration analyses (Sr, Mg, Fe and Mn), and only the least altered shells were selected for the 87Sr/86Sr analyses. The 87Sr/86Sr analyses from all the analyzed Antillean rudists resulted in average ages close to the Aptian/Albian boundary (112.56 Ma). These results show that the Antillean Coalcomana–Caprinuloidea rudist assemblage is correlative to the latest Aptian to early Albian Coalcomana interval zone from Texas and Mexico. There are, however, subtle differences in the orbitolinid foraminifer and rudist bivalve records of the Antillean Coalcomana–Caprinuloidea rudist assemblage that still need further revisions. In the Dominican Republic, for example, the orbitolinid fauna in the Central Cordillera include Coskinolinoides texanus (Keijzer), which is reported from middle Albian successions in Texas and Mexico. Moreover, the presence of primitive and advanced morphotypes of Caprinuloidea also suggests a possible bipartite division of the Coalcomana–Caprinuloidea rudist assemblage. Although the collected material from the localities with the foraminifer C. texanus and the advanced form of Caprinuloidea failed the preservation screening for 87Sr/86Sr analyses, we speculate about the possible extension of the Coalcomana–Caprinuloidea rudist assemblage from the Aptian/Albian boundary through the middle Albian.

The fluorination of mono- and bi-layer graphene have been studied by means of ab-initio DFT calculations. The stability of CF$_x$ systems are found to depend on both the F coverage and on the position of the F atoms regarding the C sublattices. When F atoms is chemisorbed to C atoms belonging to the same sublattice, low coverage is preferred. Otherwise, large F coverable is more stable (up to C$_4$F). The difference of charge distribution between the two carbon sublattices explains this finding that is confirmed by the analysis of the diffusion barriers. Binding energy of F on bi-layer systems is also computed slightly smaller than on monolayer and electronic decoupling is observed when only one of the layer is exposed to fluorine., Comment: 13 pages, 6 figures, supporting info (2 pages)

This is the Accepted Manuscript version of an article accepted for publication in Nanotechnology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6528/ab0bc1, Few-layer GaSe is one of the latest additions to the family of two-dimensional semiconducting crystals whose properties under strain are still relatively unexplored. Here, we study rippled nanosheets that exhibit a periodic compressive and tensile strain of up to 5%. The strain profile modifies the local optoelectronic properties of the alternating compressive and tensile regions, which translates into a remarkable shift of the optical absorption band-edge of up to 1.2 eV between crests and valleys. Our experimental observations are supported by theoretical results from density functional theory calculations performed for monolayers and multilayers (up to seven layers) under tensile and compressive strain. This large band gap tunability can be explained through a combined analysis of the elastic response of Ga atoms to strain and the symmetry of the wave functions, Research supported by the Spanish MINECO through Grants MAT2017–88693-R, MAT2014-57915-R, FIS2016-80434- P (AEI/FEDER, EU), BES-2015-071316, the Ramón y Cajal programme RYC-2011-09345, the Fundación Ramón Areces and the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), as well as from the Comunidad Autónoma de Madrid (CAM) MAD2D-CM Program (S2013/MIT-3007) and the European Union Seventh Framework Programme under grant agreement No. 604391 Graphene Flagship. JJP acknowledges Fulbright Fellowship for Sabbatical leave at University of Texas at Austin, EEUU. We acknowledge the computer resources and assistance provided by the Centro de Computación Científica of the Universidad Autónoma de Madrid

We study the effect of the Rashba spin-orbit interaction in the quantum transport of carbon nanotubes with arbitrary chiralities. For certain spin directions, we find a strong spin-polarized electrical current that depends on the diameter of the tube, the length of the Rashba region and on the tube chirality. Predictions for the spin-dependent conductances are presented for different families of achiral and chiral tubes. We have found that different symmetries acting on spatial and spin variables have to be considered in order to explain the relations between spin-resolved conductances in carbon nanotubes. These symmetries are more general than those employed in planar graphene systems. Our results indicate the possibility of having stable spin-polarized electrical currents in absence of external magnetic fields or magnetic impurities in carbon nanotubes., Comment: Accepted to Physical Review B. 11 pages, 10 figures, 3 tables

The new antillocaprinid rudist bivalve Parasarcolites sohli sp. nov. is described from the Maastrichtian rocks of Puerto Rico (El Rayo Formation) and Jamaica (Sunderland Inlier). The species shows that all tubes, one of the diagnostic features of the genus, arise by the development of flanges on costae to roof over the intercostal space between adjacent costae. This is the first time that this feature has been unequivocally shown in an antillocaprinid rudist and suggests that tubes in other antillocaprinid rudists arose in a similar way. The species occurs in early Maastrichtian deposits of Puerto Rico and Jamaica, and represents a potential marker species in future biostratigraphic studies.

12th International Conference on the Formation of Semiconductor Interfaces (ICFSI‐12)., We study the electronic band structure of several carbon nanotube superlattices built of two kinds of intermolecular junctions: (12, 0)/(6, 6) and (8, 0)/(14, 0). In particular, we focus on the energy bands originating from interface states. We find that in case of the metallic (12, 0)/(6, 6) superlattices, the interface bands change periodically their character from bonding- to antibonding-like vs. increasing length of the (6, 6) tube. We show that these changes are related to the decay of the charge density Friedel oscillations in the metallic (6, 6) tube. However, when we explore other chiralities without rotational symmetry, no changes in bondingantibonding character are observed for semiconductor superlattices, as exemplified in the case of (8, 0)/(14, 0) superlattices. Our results indicate that unless metallic tubes are employed in the junctions, the bondingantibonding crossings are not present.

Networks of different carbon nanotube (CNT) materials were investigated as resistive gas sensors for NO2 detection. Sensor films were fabricated by airbrushing dispersions of double-walled and multi-walled CNTs (DWNTs and MWNTs, respectively) on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250 °C in air atmosphere in order to find the optimum detection temperature. Our results indicate that CNT networks were sensitive to NO2 concentrations as low as 0.1 ppm. All tested sensors provided significantly lower response to interfering gases such as H2, NH3, toluene and octane. We demonstrate that the measured sensitivity upon exposure to NO2 strongly depends on the employed CNT material. The highest sensitivity values were obtained at temperatures ranging between 100 and 200 °C. The best sensor performance, in terms of recovery time, was however achieved at 250 °C. Issues related to the gas detection mechanisms, as well as to CNT network thermal stability in detection experiments performed in air at high operation temperatures are also discussed., This work has been supported by MEC (Spain, projects TEC2004-05098-C02-01/MIC and TEC2004-05098-C02-02/MIC, Programa I3 2006 8 0I 060) and the European Regional Development Fund (ERDF).

The Indian gharial ( Gavialis gangeticus ) is not found in saltwater, but the geographical distribution of fossil relatives suggests a derivation from ancestors that lived in, or were at least able to withstand, saline conditions. Here, we describe a new Oligocene gharial, Aktiogavialis puertoricensis , from deltaic–coastal deposits of northern Puerto Rico. It is related to a clade of Neogene gharials otherwise restricted to South America. Its geological and geographical settings, along with its phylogenetic relationships, are consistent with two scenarios: (i) that a single trans-Atlantic dispersal event during the Tertiary explains the South American Neogene gharial assemblage and (ii) that stem gharials were coastal animals and their current restriction to freshwater settings is a comparatively recent environmental shift for the group. This discovery highlights the importance of including fossil information in a phylogenetic context when assessing the ecological history of modern organisms.

Fragmentary fossils from northwestern Puerto Rico document the existence of crocodyliforms during the Late Oligocene and Early Miocene. The remains are insufficient to establish new named species, but they are inconsistent with any other crocodylian known from the western hemisphere during the Cenozoic, including extant Alligator and Crocodylus. They are thus consistent with the hypothesis that Crocodylus is a comparatively recent immigrant into the West Indies and suggest that, as with Australasia and Africa, the Antilles hosted an endemic clade of crocodylians during the Tertiary, later replaced by Crocodylus.

This paper presents sponges from the Late Cretaceous El Rayo Formation, Puerto Rico. Siliceous sponges are common fossils in the Late Cretaceous of Europe (see for example Schrammen, 1910–1912; Moret, 1926; Weidenmayer, 1994; Pisera, 1999). So far only rare siliceous sponges from the Late Cretaceous of the Caribbean region have been reported: lithistid ? Jerea Lamouroux, 1821, hexactinellids Ventriculites Mantell, 1822, and Plocoscyphia Reuss, 1846 from Trinidad (Thomas, 1935; Trechmann, 1935), and Callopegma Zittel, 1878 from the Cariblanco Formation, Puerto Rico (Howell, 1966). The sponges studied by us are heavily silicified and thus only their approximate determination was possible, but among bodily preserved sponges they are undoubtedly lithistids with tetraclone and rhizoclone desmas. Among loose spicule material, fragments of hexactinellid skeleton dominate, tetraclone and dicranoclone lithistids desmas are common, and hexactinellid lychniscosid skeletons are very rare. The island of Puerto Rico is the easternmost island of the Caribbean Greater Antilles (Fig. 1.1), a complex island arc with accreted terranes. The island is composed of Lower Jurassic to Lower Cretaceous ophiolites, Lower Cretaceous to Eocene island arc volcanic and sedimentary rocks, Middle Oligocene to Pliocene terrigenous clastics, and limestone unconformably overlying the older rocks along the north and south coasts (Santos, 1999). The pre-Oligocene rocks are divided into the southwest, central, and northeast igneous provinces (Fig. 1.2). Figure 1 — 1 , Location of the island of Puerto Rico. 2 , Location of the study area on the Sabana Grande Quadrangle. CMF–Cerro Mula Fault Zone; GSPRFZ–Great Southern Puerto Rico Fault Zone. The paleogeographic setting of the earliest island arc volcanism differed in each of the three igneous provinces (Santos, 1999). The southwest igneous province is separated from the rest of the island by the Great Southern Puerto Rico Fault Zone (Fig. 1.2). It contains …

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence., Grain boundaries and defect lines in graphene are intensively studied for their novel electronic and magnetic properties. However, there is not a complete comprehension of the appearance of localized states along these defects. Graphene grain boundaries are herein seen as the outcome of matching two semi-infinite graphene sheets with different edges. We classify the energy spectra of grain boundaries into three different types, directly related to the combination of the four basic classes of spectra of graphene edges. From the specific geometry of the grains, we are able to obtain the band structure and the number of localized states close to the Fermi energy. This provides a new understanding of states localized at grain boundaries, showing that they are derived from the edge states of graphene. Such knowledge is crucial for the ultimate tailoring of electronic and optoelectronic applications., This work was supported by the Polish National Science Center (grant DEC-2011/03/B/ST3/00091), the Basque Government through the NANOMATERIALS project (grant IE05-151) under the ETORTEK Program (iNanogune), the Spanish Ministerio de Ciencia y Tecnología (grants FIS2010-21282-C02-02, FIS2012-33521 and MONACEM projects), and the University of the Basque Country (grant no. IT-366-07).

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., We address the nature and possible observable consequences of singular one-electron states that appear when strong defects are introduced in the metallic family of graphene, namely, metallic carbon nanotubes and nanotori. In its simplest form, after creating two defects on the same sublattice, a state may emerge at the Fermi energy presenting very unusual properties: It is unique, normalizable, and features a wave function equally distributed around both defects. As a result, the exchange coupling between the magnetic moments generated by the two defects is anomalous. The intrinsic spins couple ferromagnetically, as expected, but do not present an antiferromagnetic excited state at any distance. We propose the use of metallic carbon nanotubes as an electronic device based on this anomalous coupling between spins which can be useful for the robust transmission of magnetic information at large distances. © 2014 American Physical Society., This work was supported by MICINN under Grants No. FIS2010-21883 and No. CONSOLIDER CSD2007-0010, by Generalitat Valenciana under Grant No. PROMETEO/2012/011, and by the Spanish Ministry of Economy and Competitiveness (MINECO) under Grants No. FIS2010-21282-C02-02 and No. MAT2012-33911.

We study the electronic structure of chiral and achiral graphene nanoribbons with symmetric edges, including curvature and spin-orbit effects. Curved ribbons show spin-split bands, whereas flat ribbons present spin-degenerate bands. We show that this effect is due to the breaking of spatial inversion symmetry in curved graphene nanoribbons, while flat ribbons with symmetric edges possess an inversion center, regardless of their having chiral or achiral edges. We find an enhanced edge-edge coupling and a substantial gap in narrow chiral nanoribbons, which is not present in zigzag ribbons of similar width. We attribute these size effects to the mixing of the sublattices imposed by the edge geometry, yielding a behavior of chiral ribbons that is distinct from those with pure zigzag edges. © 2013 American Physical Society., This work has been partially supported by the Spanish Ministries of Science and Innovation (MICINN) and Economy and Competitivity (MINECO) DGES under Grants No. MAT2009-14578-C03-03, No. PIB2010BZ-00512, No. FIS2010-21282-C02-02, No. FIS2011-23713, No.MAT2012-38045-C04-04, and No. FIS2012-33521.

We study the interaction energy between two graphene nanoribbons by first-principles calculations, including van der Waals interactions and spin polarization. For ultranarrow zigzag nanoribbons, the direct stacking is even more stable than the Bernal stacking, competing in energy for wider ribbons. This behavior is due to the magnetic interaction between edge states. We relate the reduction of the magnetization in zigzag nanoribbons with increasing ribbon width to the structural changes produced by the magnetic interaction, and we show that when deposited on a substrate, zigzag bilayer ribbons remain magnetic for larger widths. © 2012 American Physical Society., This work has been partially supported by the Spanish DGES under Grants No. FIS2009-08744 and No. FIS2010-19609-C02-02, the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-366-07), and the Nanoiker project (Grant No. IE11-304) under the ETORTEK program funded by the Basque Research Departament of Industry.

Trabajo presentado a la 14th edition of Trends in Nanotechnology International Conference, celebrada en Sevilla (España) del 9 al 13 de Septiembre de 2013., We prescribe general rules to predict the existence of edge states and zero-energy flat bands in graphene nanoribbons and graphene edges of arbitrary shape. [1] No calculations are needed. For the so-called minimal edges, the projection of the edge translation vector into the zigzag direction of graphene uniquely determines the edge bands. By adding nodes to minimal edges, arbitrary modified edges can be obtained; their corresponding edge bands can be found by applying hybridization rules of the extra states with those belonging to the original edge. Our prescription correctly predicts the localization and degeneracy of the zero-energy bands at one of the graphene sublattices, confirmed by tight-binding and first-principles calculations. It also allows us to qualitatively predict the existence of E≠0 bands appearing in the energy gap of certain edges and nanoribbons. We also apply these rules to graphene nanoribbons and carbon nanotubes containing ordered defect lines built of octagonal rings.[2] We show that octagonal defect lines are a robust source of state localization at the Fermi energy, in some cases leading to spontaneous magnetization. We also prove that the localization at chains of octagons is a consequence of the zigzag nature of the graphene edges forming the defect lines.

We investigate the electronic transport properties of a bilayer graphene flake contacted by two monolayer nanoribbons. Such a finite-size bilayer flake can be built by overlapping two semiinfinite ribbons or by depositing a monolayer flake onto an infinite nanoribbon. These two structures have a complementary behavior, that we study and analyze by means of a tight-binding method and a continuum Dirac model. We have found that for certain energy ranges and geometries, the conductance of these systems oscillates markedly between zero and the maximum value of the conductance, allowing for the design of electromechanical switches. Our understanding of the electronic transmission through bilayer flakes may provide a way to measure the interlayer hopping in bilayer graphene., Comment: 11 pages, 8 figures

We study the conductance of a biased bilayer graphene flake with monolayer nanoribbon contacts. We find that the transmission through the bilayer ribbon strongly depends on the applied bias between the two layers and on the relative position of the monolayer contacts. Besides the opening of an energy gap on the metallic bilayer, the bias allows to tuning the electronic density on the bilayer flake, making possible the control of the electronic transmission by an external parameter, This work was partially supported by MEC-Spain under Grant No. FIS2009-08744 and by the CSIC/CONICYT program, Grant No. 2009CL0054. J.W.G. gratefully acknowledges helpful discussions with M. Pacheco, the ICMM-CSIC for their hospitality, and the financial support of MECESUP research internship program,CONICYT (CENAVA,Grant No. ACT27), and USM 110856 internal grant

We report on the transport properties of novel carbon nanostructures made of partially unzipped carbon nanotubes, which can be regarded as a seamless junction of a tube and a nanoribbon. We find that graphene nanoribbons act at certain energy ranges as a perfect valley filters for carbon nanotubes, with the maximum possible conductance. Our results show that a partially unzipped carbon nanotube is a magnetoresistive device, with a very large value of the magnetoresistance. We explore the properties of several structures combining nanotubes and graphene nanoribbons, demonstrating that they behave as optimal contacts for each other, and opening a new route for the design of mixed graphene/nanotube devices., Comment: 4 pages, 4 figures included

We study the origin of interface states in carbon nanotube intramolecular junctions between achiral tubes. By applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated graphene layers, we are able to explain their number and energies. We show that these interface states, costumarily attributed to the presence of topological defects, are actually related to zigzag-edge states, as those of graphene zigzag nanoribbons. Spatial localization of interface states is seen to vary greatly and may extend appreciably into either side of the junction. Our results give an alternative explanation to the unusual decay length measured for interface states of semiconductor nanotube junctions and could be further tested by local probe spectroscopies., This work has been partially supported by the Spanish DGES under Grants No. MAT2006-06242 and No. FIS2007-66711-C02-C01 and Spanish CSIC under Grant No. PI 200860I048. W.J. and M.P. acknowledge financial support from Polish LFPPI.

Multi-walled carbon nanotube (MWNT) networks were investigated as resistive gas sensors for nitrogen dioxide detection. Sensor films were fabricated by airbrushing MWNT dispersions on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250degC in air atmosphere, in order to find the optimum detection temperature. The best response to NO2 was obtained at 25degC. The tested MWNT sensors were sensitive to low NO2 concentrations in air atmosphere. Moreover, these sensors provided no response to interfering gases such as H2, NH3, toluene and octane. Thermal treatments, based in repeated heating and cooling of the films, increased the sensor response to NO2.

Single-walled carbon nanotube (SWNT) networks were tested as gas sensors for nitrogen dioxide detection. Sensor films were fabricated by airbrushing SWNT dispersions on alumina substrates. Sensors were characterized by resistance measurements from 25 to 200degC. The best response to NO2 was obtained at 200degC. The tested SWNT sensors were sensitive to low NO2 concentrations in nitrogen and air atmospheres. Moreover, these sensors provided no response to interfering gases such as H2, NH3, toluene and octane. The effect of thermal treatments on the sensor response was also investigated.

Proceedings of the XXXVII International School of Semiconducting Compounds, Jaszowiec 2008., Interface states of all-metallic carbon nanotube quantum dots and superlattices are studied within a tight-binding model. We focus on achiral systems made by connecting armchair (n; n) and zigzag (2n; 0) tubes with a full ring of n pentagon-heptagon topological defects. We show that the coupling between interface states, which arise from the topological defects, re°ects the existence of the Friedel oscillations in the (n; n) tube, with an unusually large decay exponent. We expect this interaction to be important for the understanding of other physical properties, such as selective dot growth, magnetic interaction through carbon tubes or optical spectroscopy of interface states., We acknowledge financial support by the ETORTEK (NANOMAT) program of the Basque government, the Intramural Special Project (Ref. 2006601242), the Spanish Ministerio de Ciencia y Tecnologia (Grants No. Fis 2007-66711-C02-C01 and MAT2006-06242), JCCM Grant No. PAI08-0067-2673 and the European Network of Excellence NANOQUANTA (NM4-CT-2004-500198).

9 páginas, 11 figuras.-- PACS numbers: 81.05.U-, 73.20.-r, 73.63.Fg, 85.75.-d, The properties of carbon nano-tubes can be dramatically altered by the presence of defects. In this work we address the properties of two different kinds of defective nano-tubes: junctions of achiral tubes with topological defects and partially unzipped carbon nano-tubes. In particular, we begin by focussing on the interface states in carbon nanotube junctions between achiral tubes. We show that their number and energies can be derived by applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated semi-infinite graphene layers. We show that these interface states, which were thought to be due to the presence of topological defects, are in fact related to the graphene zigzag edge states. Secondly, we study partially unzipped carbon nano-tubes, which can be considered as the junction of a carbon nanotube and a graphene nanoribbon, which has edge features giving rise to novel properties. Carbon nanoribbons act as transparent contacts for nano-tubes and viceversa, yielding a high conductance. At certain energies, nanoribbons behave as valley filters for carbon nano-tubes; This holds considering electron-electron interaction effects. Furthermore, the application of a magnetic field turns the system conducting, with a 100% magnetoresistance. These novel structures may open a way for new carbon-based devices., This work has been partially supported by the Spanish DGES under grants MAT2006-06242, MAT2006-03741 and FIS2007-66711-C02-C01 and Spanish CSIC under grant PI 200860I048. W.J. and M.P. acknowledge financial support from Polish LFPPI.

We investigate the electronic transport properties of a bilayer graphene ake contacted by two monolayer nanoribbons. This nite-size bilayer ake can be built by overlapping two semi-in nite ribbons. We study and analyze the electronic behavior of this structure by means of a tight-binding method and a continuum Dirac model. We have found that the conductance oscillates markedly between zero and the maximum value of the conductance, allowing for the design of electromechanical switches.