Structure-dependent electrical properties of graphene nanoribbon devices with graphene electrodes

Graphene nanoribbons (GNRs) are a novel and intriguing class of materials in the field of nanoelectronics, since their properties, solely defined by their width and edge type, are controllable with high precision directly from synthesis. Here we study the correlation between the GNR structure and the corresponding device electrical properties. We investigated a series of field effect devices consisting of a film of armchair GNRs with different structures (namely width and/or length) as the transistor channel, contacted with narrowly spaced graphene sheets as the source-drain electrodes. By analyzing several tens of junctions for each individual GNR type, we observe that the values of the output current display a width-dependent behavior, indicating electronic bandgaps in good agreement with the predicted theoretical values. These results provide insights into the link between the ribbon structure and the device properties, which are fundamental for the development of GNR-based electronics.Comment: Published in Carbon (2019

Edge Disorder in Bottom-Up Zigzag Graphene Nanoribbons: Implications for Magnetism and Quantum Electronic Transport

We unveil the nature of the structural disorder in bottom-up zigzag graphene nanoribbons along with its effect on the magnetism and electronic transport on the basis of scanning probe microscopies and first-principles calculations. We find that edge-missing m-xylene units emerging during the cyclodehydrogenation step of the on-surface synthesis are the most common point defects. These "bite'' defects act as spin-1 paramagnetic centers, severely disrupt the conductance spectrum around the band extrema, and give rise to spin-polarized charge transport. We further show that the electronic conductance across graphene nanoribbons is more sensitive to "bite" defects forming at the zigzag edges than at the armchair ones. Our work establishes a comprehensive understanding of the low-energy electronic properties of disordered bottom-up graphene nanoribbons

Quantum Electronic Transport Across "Bite" Defects in Graphene Nanoribbons

On-surface synthesis has recently emerged as an effective route towards the atomically precise fabrication of graphene nanoribbons of controlled topologies and widths. However, whether and to which degree structural disorder occurs in the resulting samples is a crucial issue for prospective applications that remains to be explored. Here, we experimentally identify missing benzene rings at the edges, which we name "bite" defects, as the most abundant type of disorder in armchair nanoribbons synthesized by the bottom-up approach. First, we address their density and spatial distribution on the basis of scanning tunnelling microscopy and find that they exhibit a strong tendency to aggregate. Next, we explore their effect on the quantum charge transport from first-principles calculations, revealing that such imperfections substantially disrupt the conduction properties at the band edges. Finally, we generalize our theoretical findings to wider nanoribbons in a systematic manner, hence establishing practical guidelines to minimize the detrimental role of such defects on the charge transport. Overall, our work portrays a detailed picture of "bite" defects in bottom-up armchair graphene nanoribbons and assesses their effect on the performance of carbon-based nanoelectronic devices

MoRe Electrodes with 10-nm Nanogaps for Electrical Contact to Atomically Precise Graphene Nanoribbons

Atomically precise graphene nanoribbons (GNRs) are predicted to exhibit exceptional edge-related properties, such as localized edge states, spin polarization, and half-metallicity. However, the absence of low-resistance nano-scale electrical contacts to the GNRs hinders harnessing their properties in field-effect transistors. In this paper, we make electrical contact with 9-atom-wide armchair GNRs using superconducting alloy MoRe as well as Pd (as a reference), which are two of the metals providing low-resistance contacts to carbon nanotubes. We take a step towards contacting a single GNR by fabrication of electrodes with a needle-like geometry, with about 20 nm tip diameter and 10 nm separation. To preserve the nano-scale geometry of the contacts, we develop a PMMA-assisted technique to transfer the GNRs onto the pre-patterned electrodes. Our device characterizations as a function of bias-voltage and temperature, show a thermally-activated gate-tunable conductance in the GNR-MoRe-based transistors.Comment: Main text: 17 pages, 4 figures Supporting information: 19 pages, 9 figure

MoRe Electrodes with 10 nm Nanogaps for Electrical Contact to Atomically Precise Graphene Nanoribbons.

Atomically precise graphene nanoribbons (GNRs) are predicted to exhibit exceptional edge-related properties, such as localized edge states, spin polarization, and half-metallicity. However, the absence of low-resistance nanoscale electrical contacts to the GNRs hinders harnessing their properties in field-effect transistors. In this paper, we make electrical contact with nine-atom-wide armchair GNRs using superconducting alloy MoRe as well as Pd (as a reference), which are two of the metals providing low-resistance contacts to carbon nanotubes. We take a step toward contacting a single GNR by fabricating electrodes with needlelike geometry, with about 20 nm tip diameter and 10 nm separation. To preserve the nanoscale geometry of the contacts, we develop a PMMA-assisted technique to transfer the GNRs onto the prepatterned electrodes. Our device characterizations as a function of bias voltage and temperature show thermally activated gate-tunable conductance in GNR-MoRe-based transistors

Scaling and statistics of bottom-up synthesized armchair graphene nanoribbon transistors

Bottom-up assembled nanomaterials and nanostructures allow for the studies of rich and unprecedented quantum-related and mesoscopic transport phenomena. However, it can be difficult to quantify the correlations between the geometrical or structural parameters obtained from advanced microscopy and measured electrical characteristics when they are made into macroscopic devices. Here, we propose a strategy to connect the nanomaterial morphologies and the device performance through a Monte Carlo device model and apply it to understand the scaling trends of bottom-up synthesized armchair graphene nanoribbon (GNR) transistors. A new nanofabrication process is developed for GNR transistors with channel length down to 7 nm. The impacts of the GNR spatial distributions and the device geometries on the device performance are investigated systematically through comparison of experimental data with the model. Through this study, challenges and opportunities of transistor technologies based on bottom-up synthesized GNRs are pinpointed, paving the way to the further improvement of the GNR device performance for future transistor technology nodes

Application of the Fugl-Meyer Assessment (FMA) and the Wolf Motor Function Test (WMFT) in the recovery of upper limb function in patients after chronic stroke: a literature review

Estima-se que de 45 a 75% dos adultos que sofreram um Acidente Vascular Encefálico (AVE) têm dificuldade de utilizar o membro superior (MS) hemiparético nas atividades de vida diária (AVD’s) na fase crônica. Escalas funcionais são utilizadas na prática da reabilitação e em pesquisas para diagnósticos, prognósticos e resposta a tratamentos. As escalas Wolf Motor Function Test (WMFT) e Fugl-Meyer Assessment (FMA) são instrumentos muito citados na literatura. Objetivo: O objetivo deste estudo foi verificar a aplicação das escalas WMFT e FMA na recuperação funcional do membro superior em pacientes pós AVE crônico. Método: Foi realizada uma revisão de literatura com busca nas bases de dados do MedLine (PubMed) de artigos publicados de 2000 a 2013. Adotou-se como estratégia de pesquisa o método (P.I.C.O.). Os descritores utilizados para a pesquisa foram: (stroke OR cerebrovascular disorders OR intracranial arteriosclerosis OR intracranial embolism and thrombosis) AND (fugl-meyer assessment OR wolf motor function test). Foi utilizado therapy narrow como filtro de busca. Resultados: Foram encontrados 181 estudos, 89 foram eliminados por não preencherem os critérios de inclusão ou por não apresentarem tema relevante à pesquisa. Após a seleção por título e resumo, 92 artigos foram lidos na íntegra. Destes, 47 foram excluídos por não contemplarem o objetivo da presente pesquisa. No total, 45 artigos foram revisados. Houve predomínio da utilização da ferramenta FMA e verificouse que 80% dos estudos aplicaram esta escala para avaliar respostas a diferentes tipos de terapias. Nestes estudos, a intervenção mais utilizada foi a Terapia de Contensão Induzida (TCI) (25%), seguida pela Terapia Robótica (22,2%). Apesar do WMFT ter sido inicialmente desenvolvido para avaliar os efeitos da TCI, nos dias de hoje verifica-se sua utilização para avaliar a recuperação funcional de pacientes com sequelas de AVE após aplicação de outras técnicas. Em nossa pesquisa, 44,4% dos estudos utilizaram o WMFT, destes, 35% avaliaram os efeitos da TCI, 15% da terapia robótica de MS e 65% usaram diferentes terapias. Conclusão: Em estudos controlados randomizados, a FMA foi a escala mais utilizada para avaliar a recuperação funcional do MS em pacientes com AVE crônico, inclusive após aplicação de terapia robótica. Porém, verificamos que ela não é a escala mais indicada para avaliar os mesmos desfechos após utilização da TCI. Entretanto, a WMFT foi a escala mais utilizada para avaliação funcional após aplicação da TCI e mostrou-se mais sensível que a FMA na terapia bilateral, além de alta aplicabilidade na terapia de realidade virtual.It is estimated that 45-75% of chronic adult stroke patients have difficulty in using the hemiparetic upper limb (MS) in their daily life activities (DLAs). Functional scales are used in the practice of rehabilitation, in the search for diagnoses and prognoses, and in evaluating response to treatment. The Wolf Motor Function Test (WMFT) and Fugl-Meyer Assessment (FMA) scales are the instruments most commonly mentioned in the literature. Objective: The aim of this study was to review the use of the WMFT and FMA scales in the recovery of upper limb function in patients after chronic stroke. Method: We searched the MedLine database (PubMed) for articles published from 2000 to 2013. The PICO method was adopted as the search strategy. The descriptors used for the search were: (stroke OR cerebrovascular disorders OR intracranial arteriosclerosis OR thrombosis intracranial embolism) AND (Fugl-Meyer assessment OR wolf motor function test). Therapy/narrow was used as a search filter. Results: We found 181 studies, 89 of which were excluded because they did not meet the inclusion criteria or did not have a topic relevant to the review search. After selection by title and by abstract, 92 articles were fully read. Of these articles, 47 were excluded because they did not fulfil the search objective. All in all, 45 articles were reviewed. FMA is the tool most used and it was found that 80% of the studies applied this scale to evaluate responses to the different therapies. In these studies, the intervention most used was the Constrained Induced Therapy (CIT) (25%), followed by Robotics Therapy (22.2%). Although the WMFT was initially developed to assess the effects of CIT, nowadays this scale is used, after the application of other techniques, to assess the functional recovery of patients with stroke sequelae. In our survey, 44.4% of the studies used WMFT; of these, 35% assessed the effects of CIT, 15% assessed robotic therapy for the upper limbs, and 65% for different therapies. Conclusion: For randomized controlled trials, the FMA scale was more used to assess functional recovery in the upper limbs of chronic stroke patients, even after application of robotics therapy. However, we found that it is not the most appropriate scale to assess the same outcomes after CIT use. WMFT is the scale most widely used for functional assessment after application of CIT; it is more sensitive than FMA for bilateral therapy, and is highly applicable in virtual reality therapy

Engineering of robust topological quantum phases in graphene nanoribbons

Here we present a flexible strategy to realize robust nanomaterials exhibiting valence electronic structures whose fundamental physics is described by the SSH-Hamiltonian. These solid-state materials are realized using atomically precise graphene nanoribbons (GNR). We demonstrate the controlled periodic coupling of topological boundary states at junctions of armchair GNRs of different widths to create quasi-1D trivial and non-trivial electronic quantum phases. Their topological class is experimentally determined by drawing upon the bulk-boundary correspondence and measuring the presence (non-trivial) or absence (trivial) of localized end states by scanning tunneling spectroscopy (STS). The strategy we propose has the potential to tune the band width of the topological electronic bands close to the energy scale of proximity induced spin-orbit coupling or superconductivity, and may allow the realization of Kitaev like Hamiltonians and Majorana type end states

Influence of invertor and evertor muscle fatigue on functional jump tests and postural control: A prospective cross-sectional study

Objective: Fatigue of the ankle's stabilizing muscles may influence the performance of functional activities and postural control. The purpose of this study was to evaluate the performance of healthy young adults using functional jump tests and static posturography control under pre- and post-fatigue conditions of the ankle invertor and evertor muscles. Methods: Thirty physically active healthy male and female (15 male and 15 female) volunteers (24.3 years) were enrolled in this prospective cross-sectional study. Participants performed tests on one day under a non-fatigued state of invertor and evertor muscles and on the second day in a fatigued state. Tests included static posturography on a force platform in a bipedal stance with eyes open and closed and in one-legged support with eyes open and functional jump tests (figure-of-8, side hop, 6-m crossover hop, and square hop). Fatigue of the ankle invertor and evertor muscles was induced using isokinetic dynamometry with 30 repetitions at 120°/s. Results: Participants had an average age of 24.3 years (SD ± 2.08), the height of 1.73 m (SD ± 0.08), and a weight of 68.63 kg (SD ± 10.29). The average Body Mass Index (BMI) was 22.88 (SD ± 2.46). A decrease in performance was observed in functional activities and postural control under all conditions after the induction of muscle fatigue, except for the speed at a bipedal stance with eyes open. Conclusions: Functional jump tests are low cost and useful for clinical practice and evaluation of the effects of muscle fatigue and could be used in clinical practice

Control postural dinámico y estático de jugadores de vóley con amputación transfemoral

Introdução: Uma diminuição no controle postural e propriocepção é um resultado comum da amputação dos membros inferiores. No entanto, a adaptação do controle postural nos jogadores paralímpicos de vôlei sentado com amputação de membros inferiores ainda não é compreendida. Objetivo: O propósito desse estudo transversal controlado consistia em investigar o controle postural estático e dinâmico em jogadores de vôlei sentado com amputação transfemoral unilateral. Métodos: Dezesseis indivíduos participaram do estudo, oito deles eram amputados com amputação transfemoral unilateral (grupo amputado: idade: 33,5 ± 5,6 anos, peso: 77,7 ± 5,3 kg, altura: 179,4 ± 5,3 cm) e oito eram fisicamente ativos não-amputados (idade do grupo controle: 27,2 ± 8,4 anos, peso: 82,7 ± 6,6 kg, altura: 178,7 ± 6,1 cm). O controle postural estático e dinâmico foi avaliado usando a plataforma Neurocom® Balance Master System (Teste Clínico Modificado de Interação Sensorial no Equilíbrio, Limites de Estabilidade, Variação Rítmica de Carga, Sentado para de Pé, Marcha na Plataforma e Passo com Inversão Rápida). As análises estatísticas foram realizadas com o teste Shapiro-Wilk, o teste de Levene e o teste t de Student para amostras pareadas (p 0,05). Conclusão: Apesar do treinamento no vôlei sentado, nossos resultados demonstraram que os amputados apresentam um controle postural mais precário tanto em tarefas estáticas como dinâmicas, quando comparados com os não-amputados fisicamente ativos. Nível de Evidência II; Estudo prognóstico - investigar o efeito da característica do paciente no resultado de uma doença/Estudo Retrospectivo.Introduction: A decrease in postural control and proprioception is a common result of lower limb amputation. However, postural control adaptation in Paralympic sitting volleyball players with lower limb amputation is not yet understood. Objective: The purpose of this cross-sectional controlled study was to investigate static and dynamic postural control in sitting volleyball players with unilateral transfemoral amputation. Methods: Sixteen subjects participated in the study, eight of whom were amputees with unilateral transfemoral amputation (amputee group: age: 33.5 ± 5.6 years, weight: 77.7 ± 5.3 kg, height: 179.4 ± 5.3 cm) and eight physically active non-amputees (control group age: 27.2 ± 8.4 years, weight: 82.7 ± 6.6 kg, height: 178.7 ± 6.1 cm). Static and dynamic postural control was evaluated using the Neurocom® Balance Master System platform (Modified Clinical Test of Sensory Interaction on Balance, Limits of Stability, Rhythmic Weight Shift, Sit-to-Stand, Walk Across, and Step and Quick Turn). Statistical analyses were performed with the Shapiro-Wilk test, Levene's test, and Student's t-test for paired samples (p .05). Conclusion: Despite training in sitting volleyball, our results demonstrated that amputees have poorer postural control in both static and dynamic tasks when compared to physically active non-amputees. Level of Evidence II; Prognostic Studies—Investigating the Effect of a Patient Characteristic on Disease Outcome / Retrospectivef Study.Introducción: Una disminución en el control postural y propiocepción es un resultado común de la amputación de los miembros inferiores. Sin embargo, la adaptación del control postural en los jugadores paralímpicos de vóley sentado con amputación de miembros inferiores aún no es comprendida. Objetivo: El propósito de ese estudio transversal controlado consistía en investigar el control postural estático y dinámico en jugadores de vóley sentado con amputación transfemoral unilateral. Métodos: Dieciséis individuos participaron en el estudio, ocho de ellos eran amputados con amputación transfemoral unilateral (grupo amputado: edad: 33,5 ± 5,6 años, peso: 77,7 ± 5,3 kg, altura: 179,4 ± 5,3 cm) y ocho eran físicamente activos no amputados (edad del grupo control: 27,2 ± 8,4 años, peso: 82,7 ± 6,6 kg, altura: 178,7 ± 6,1 cm). El control postural estático y dinámico fue evaluado usando la plataforma Neurocom® Balance Master System (Test Clínico Modificado de Interacción Sensorial en el Equilibrio, Límites de Estabilidad, Variación Rítmica de Carga, Sentado para de pie, Marcha en la Plataforma y Paso con Inversión Rápida). Los análisis estadísticos fueron realizados con el test Shapiro-Wilk, el test de Levene y el test t de Student para muestras pareadas (p 0,05). Conclusión: A pesar del entrenamiento en el vóley sentado, nuestros resultados demostraron que los amputados presentan un control postural más precario tanto en tareas estáticas como dinámicas, cuando comparados con los no amputados físicamente activos. Nivel de Evidencia II; Estudio pronóstico - investigar el efecto de la característica del paciente en el resultado de una enfermedad/Estudio Retrospectivo