Electronic and transport properties of 2D Dirac materials: graphene and topological insulators.

156 p.This thesis presents a set of contributions to the field of 2D Dirac materials, which have emerged as promising candidates for future nanoelectronics. The electronic and transport properties of various graphene-based nanostructures and surfaces of topological insulators reported in this work, provide further insight into the functionalities of this class of materials. For the characterization of the materials reported in this thesis, we applied DFT and a NEGF approach.Most graphene-based electronic devices, require the formation of contacts between the 2D material and metal electrodes. Within this context, it is crucial to design graphene-metal interfaces with low contact resistances. In this work, we analyzed the structural evolution and transport properties of various metal-graphene contacts with and without functionalization or contamination of the graphene edge, with special focus on their influence on the contact resistance. For metal-graphene edge contacts, we found a strong metal dependence of the stability on graphene edge contaminants. In general, we found the contact resistance to increase upon graphene edge contamination, although the strength of the relative increment dependent significantly on the metal and edge contamination. Nevertheless, our study provides valuable insight into the mechanisms responsible for device-to-device variations of metal-graphene contacts in experiments.Further, we studied the electronic and transport properties of a novel type of graphene nanoribbon (GNR) and the nanoporous graphene (NPG) derived from it. Our characterization of the electronic properties of the NPG revealed that, like the ribbon, it is a semiconductor. Furthermore, it inherits uniquely localized states from ribbon, which form a 1D band dispersing in the direction perpendicular to the ribbon's backbone. Moreover, we found states localized in the vacuum region of the ribbon. Within the NPG, these states interact with each other, forming bonding and anti-bonding pore states. STM experiments have confirmed the existence of these pore states and demonstrated the uniform growth of the NPG over a larger area. Due to its semiconducting behavior, this NPG offers high potential for many electronic applications (e.g., FETs), as well as for molecular sensing and sieving applications.Due to their extraordinary properties, topological insulators (TIs) have been proposed for a wide range of applications, especially for spintronics. With the aim of spintronic applications, the challenge in this field is to find a TI with a surface state protected against magnetic perturbations. Within this context, we investigate the influence of chemical disorder on the structural and magnetic properties of a Co adsorbed on the surface of a given ternary TI surface. In combination with experiments, we could demonstrate that Co tends to adsorbed away from the high-symmetry position whenever it is surrounded by different species of the TI's surface atoms. This adsorption behavior leads to a reduced hybridization between Co and the TI's surface state and, consequently, the surface state is still protected by time-reversal symmetry.Similar results can be expected for other ternary TI's with chemical disorder in the surface layer.DIPC. Donostia International Physics Cente

Electronic and transport properties of 2D Dirac materials: graphene and topological insulators.

156 p.This thesis presents a set of contributions to the field of 2D Dirac materials, which have emerged as promising candidates for future nanoelectronics. The electronic and transport properties of various graphene-based nanostructures and surfaces of topological insulators reported in this work, provide further insight into the functionalities of this class of materials. For the characterization of the materials reported in this thesis, we applied DFT and a NEGF approach.Most graphene-based electronic devices, require the formation of contacts between the 2D material and metal electrodes. Within this context, it is crucial to design graphene-metal interfaces with low contact resistances. In this work, we analyzed the structural evolution and transport properties of various metal-graphene contacts with and without functionalization or contamination of the graphene edge, with special focus on their influence on the contact resistance. For metal-graphene edge contacts, we found a strong metal dependence of the stability on graphene edge contaminants. In general, we found the contact resistance to increase upon graphene edge contamination, although the strength of the relative increment dependent significantly on the metal and edge contamination. Nevertheless, our study provides valuable insight into the mechanisms responsible for device-to-device variations of metal-graphene contacts in experiments.Further, we studied the electronic and transport properties of a novel type of graphene nanoribbon (GNR) and the nanoporous graphene (NPG) derived from it. Our characterization of the electronic properties of the NPG revealed that, like the ribbon, it is a semiconductor. Furthermore, it inherits uniquely localized states from ribbon, which form a 1D band dispersing in the direction perpendicular to the ribbon's backbone. Moreover, we found states localized in the vacuum region of the ribbon. Within the NPG, these states interact with each other, forming bonding and anti-bonding pore states. STM experiments have confirmed the existence of these pore states and demonstrated the uniform growth of the NPG over a larger area. Due to its semiconducting behavior, this NPG offers high potential for many electronic applications (e.g., FETs), as well as for molecular sensing and sieving applications.Due to their extraordinary properties, topological insulators (TIs) have been proposed for a wide range of applications, especially for spintronics. With the aim of spintronic applications, the challenge in this field is to find a TI with a surface state protected against magnetic perturbations. Within this context, we investigate the influence of chemical disorder on the structural and magnetic properties of a Co adsorbed on the surface of a given ternary TI surface. In combination with experiments, we could demonstrate that Co tends to adsorbed away from the high-symmetry position whenever it is surrounded by different species of the TI's surface atoms. This adsorption behavior leads to a reduced hybridization between Co and the TI's surface state and, consequently, the surface state is still protected by time-reversal symmetry.Similar results can be expected for other ternary TI's with chemical disorder in the surface layer.DIPC. Donostia International Physics Cente

Bottom-up synthesis of multifunctional nanoporous graphene

Nanosize pores can turn semimetallic graphene into a semiconductor and, from being impermeable, into the most efficient molecular-sieve membrane. However, scaling the pores down to the nanometer, while fulfilling the tight structural constraints imposed by applications, represents an enormous challenge for present top-down strategies. Here we report a bottom-up method to synthesize nanoporous graphene comprising an ordered array of pores separated by ribbons, which can be tuned down to the 1-nanometer range. The size, density, morphology, and chemical composition of the pores are defined with atomic precision by the design of the molecular precursors. Our electronic characterization further reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ∼1 electron volt coexist with confined pore states, making the nanoporous graphene a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species

Expansion-enhanced super-resolution radial fluctuations enable nanoscale molecular profiling of pathology specimens

Expansion microscopy physically enlarges biological specimens to achieve nanoscale resolution using diffraction-limited microscopy systems1. However, optimal performance is usually reached using laser-based systems (for example, confocal microscopy), restricting its broad applicability in clinical pathology, as most centres have access only to light-emitting diode (LED)-based widefield systems. As a possible alternative, a computational method for image resolution enhancement, namely, super-resolution radial fluctuations (SRRF)2,3, has recently been developed. However, this method has not been explored in pathology specimens to date, because on its own, it does not achieve sufficient resolution for routine clinical use. Here, we report expansion-enhanced super-resolution radial fluctuations (ExSRRF), a simple, robust, scalable and accessible workflow that provides a resolution of up to 25 nm using LED-based widefield microscopy. ExSRRF enables molecular profiling of subcellular structures from archival formalin-fixed paraffin-embedded tissues in complex clinical and experimental specimens, including ischaemic, degenerative, neoplastic, genetic and immune-mediated disorders. Furthermore, as examples of its potential application to experimental and clinical pathology, we show that ExSRRF can be used to identify and quantify classical features of endoplasmic reticulum stress in the murine ischaemic kidney and diagnostic ultrastructural features in human kidney biopsies.</p

Accumulation of α-synuclein mediates podocyte injury in Fabry nephropathy

Current therapies for Fabry disease are based on reversing intracellular accumulation of globotriaosylceramide (Gb3) by enzyme replacement therapy (ERT) or chaperone-mediated stabilization of the defective enzyme, thereby alleviating lysosomal dysfunction. However, their effect in the reversal of end-organ damage, like kidney injury and chronic kidney disease, remains unclear. In this study, ultrastructural analysis of serial human kidney biopsies showed that long-term use of ERT reduced Gb3 accumulation in podocytes but did not reverse podocyte injury. Then, a CRISPR/Cas9–mediated α-galactosidase knockout podocyte cell line confirmed ERT-mediated reversal of Gb3 accumulation without resolution of lysosomal dysfunction. Transcriptome-based connectivity mapping and SILAC-based quantitative proteomics identified α-synuclein (SNCA) accumulation as a key event mediating podocyte injury. Genetic and pharmacological inhibition of SNCA improved lysosomal structure and function in Fabry podocytes, exceeding the benefits of ERT. Together, this work reconceptualizes Fabry-associated cell injury beyond Gb3 accumulation, and introduces SNCA modulation as a potential intervention, especially for patients with Fabry nephropathy.publishedVersio

Comparative analysis of Neph gene expression in mouse and chicken development

Neph proteins are evolutionarily conserved members of the immunoglobulin superfamily of adhesion proteins and regulate morphogenesis and patterning of different tissues. They share a common protein structure consisting of extracellular immunoglobulin-like domains, a transmembrane region, and a carboxyl terminal cytoplasmic tail required for signaling. Neph orthologs have been widely characterized in invertebrates where they mediate such diverse processes as neural development, synaptogenesis, or myoblast fusion. Vertebrate Neph proteins have been described first at the glomerular filtration barrier of the kidney. Recently, there has been accumulating evidence suggesting a function of Neph proteins also outside the kidney. Here we demonstrate that Neph1, Neph2, and Neph3 are expressed differentially in various tissues during ontogenesis in mouse and chicken. Neph1 and Neph2 were found to be amply expressed in the central nervous system while Neph3 expression remained localized to the cerebellum anlage and the spinal cord. Outside the nervous system, Neph mRNAs were also differentially expressed in branchial arches, somites, heart, lung bud, and apical ectodermal ridge. Our findings support the concept that vertebrate Neph proteins, similarly to their Drosophila and C. elegans orthologs, provide guidance cues for cell recognition and tissue patterning in various organs which may open interesting perspectives for future research on Neph1-3 controlled morphogenesis

Peri-operative red blood cell transfusion in neonates and infants: NEonate and Children audiT of Anaesthesia pRactice IN Europe: A prospective European multicentre observational study

BACKGROUND: Little is known about current clinical practice concerning peri-operative red blood cell transfusion in neonates and small infants. Guidelines suggest transfusions based on haemoglobin thresholds ranging from 8.5 to 12 g dl-1, distinguishing between children from birth to day 7 (week 1), from day 8 to day 14 (week 2) or from day 15 (≥week 3) onwards. OBJECTIVE: To observe peri-operative red blood cell transfusion practice according to guidelines in relation to patient outcome. DESIGN: A multicentre observational study. SETTING: The NEonate-Children sTudy of Anaesthesia pRactice IN Europe (NECTARINE) trial recruited patients up to 60 weeks' postmenstrual age undergoing anaesthesia for surgical or diagnostic procedures from 165 centres in 31 European countries between March 2016 and January 2017. PATIENTS: The data included 5609 patients undergoing 6542 procedures. Inclusion criteria was a peri-operative red blood cell transfusion. MAIN OUTCOME MEASURES: The primary endpoint was the haemoglobin level triggering a transfusion for neonates in week 1, week 2 and week 3. Secondary endpoints were transfusion volumes, 'delta haemoglobin' (preprocedure - transfusion-triggering) and 30-day and 90-day morbidity and mortality. RESULTS: Peri-operative red blood cell transfusions were recorded during 447 procedures (6.9%). The median haemoglobin levels triggering a transfusion were 9.6 [IQR 8.7 to 10.9] g dl-1 for neonates in week 1, 9.6 [7.7 to 10.4] g dl-1 in week 2 and 8.0 [7.3 to 9.0] g dl-1 in week 3. The median transfusion volume was 17.1 [11.1 to 26.4] ml kg-1 with a median delta haemoglobin of 1.8 [0.0 to 3.6] g dl-1. Thirty-day morbidity was 47.8% with an overall mortality of 11.3%. CONCLUSIONS: Results indicate lower transfusion-triggering haemoglobin thresholds in clinical practice than suggested by current guidelines. The high morbidity and mortality of this NECTARINE sub-cohort calls for investigative action and evidence-based guidelines addressing peri-operative red blood cell transfusions strategies. TRIAL REGISTRATION: ClinicalTrials.gov, identifier: NCT02350348

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe