92 research outputs found

    Field emission from two-dimensional GeAs

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    GeAs is a layered material of the IV-V groups that is attracting growing attention for possible applications in electronic and optoelectronic devices. In this study, exfoliated multilayer GeAs nanoflakes are structurally characterized and used as the channel of back-gate field-effect transistors. It is shown that their gate-modulated p-type conduction is decreased by exposure to light or electron beam. Moreover, the observation of a field emission current demonstrates the suitability of GeAs nanoflakes as cold cathodes for electron emission and opens up new perspective applications of two-dimensional GeAs in vacuum electronics. Field emission occurs with a turn-on field of ~80 V/{\mu}m and attains a current density higher than 10 A/cm^2, following the general Fowler-Nordheim model with high reproducibility.Comment: 10 pages, 3 figure

    Local Characterization of Field Emission Properties of Graphene Flowers

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    An experimental study about field emission properties of commercially available graphene flowers cloth is reported. Material characterization by means of x-ray diffraction, Raman spectroscopy, and x-ray photoemission spectroscopy confirms the formation of high quality vertical few-layers graphene nanosheets. A tip-anode setup is exploited in which nanomanipulated tungsten tip is used as the anode at controlled distance from the emitter in order to reduce the effective emitting area below 1 μm2, giving access to local characterization. A turn-on field as low as 0.07 V nm−1 and field enhancement factor up to 32 for very small cathode–anode separation distances is demonstrated, in the range 400–700 nm. It is also shown that the turn-on field increases for increasing distances, while the field enhancement factor decreases. Finally, time stability of the field emission current is reported, evidencing a reduction of the fluctuations for lower current levels

    Side-gate leakage and field emission in all-graphene field effect transistors on SiO2/Si substrate

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    We fabricate planar all-graphene field-effect transistors with self-aligned side-gates at 100 nm from the main graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at high voltages. We report a field-emission current density as high as 1uA/um between graphene flakes. These findings are essential for the miniaturization of atomically thin devices

    Side-gate leakage and field emission in all-graphene field effect transistors on SiO2/Si substrate

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    We fabricate planar all-graphene field-effect transistors with self-aligned side-gates at 100 nm from the main graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at high voltages. We report a field-emission current density as high as 1uA/um between graphene flakes. These findings are essential for the miniaturization of atomically thin devices.Comment: Research article, 8 pages, 5 figure

    Photoresponse Study of MWCNTS/Insulator/n-Type Si/Insulator/Metal Heterostructure as a Function of the Density of MWCNTs Layer

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    In this work devices based on a MWCNTs-Si heterojunction were realized growing MWCNTs, by chemical vapor deposition, on an n-type Si substrate with the top and bottom surfaces covered by 140 nm thick Si3N4 layers. Two metal contacts, realized on the top and back of the Si surface, were used to perform I-V measurements of the vertical heterostructure. The photocurrent behavior, obtained by light illumination, was studied as a function of the thickness of the MWCNTs layer. A planar quantum efficiency map of the device was obtained by I-V measure when the active area of the device was rastered by a 1 mm diameter light spot. The thickness reduction of the MWCNTs was realized by adhesive tape. We found that the photocurrent intensity increased when the density of the MWCNTs layer was decreased. To check the substrate coverage by the MWCNTs, scanning electron microscope images were taken

    Advances on Sensors Based on Carbon Nanotubes

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    Carbon nanotubes have been attracting considerable interest among material scientists, physicists, chemists, and engineers for almost 30 years. Owing to their high aspect ratio, coupled with remarkable mechanical, electronic, and thermal properties, carbon nanotubes have found application in diverse fields. In this review, we will cover the work on carbon nanotubes used for sensing applications. In particular, we will see examples where carbon nanotubes act as main players in devices sensing biomolecules, gas, light or pressure changes. Furthermore, we will discuss how to improve the performance of carbon nanotube-based sensors after proper modification

    The role of nanoscale topography on super-hydrophobicity: a study of fluoro-based polymer film on vertical carbon nanotubes

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    The unique electronic, mechanical and chemical properties of carbon nanotubes make them most promising candidates for the building blocks of molecular-scale machines, and nanoelectronic devices. On the other hand, highly hydrophobic films are being actively considered in silicon based micro-electromechanical systems, nanotechnology based devices, optoelectronic devices, or biomedical devices to reduce adhesion that may be encountered during wet processing. In order to fill the gap, and fulfill the requirements, it could be proved that morphological changes in the nanometer range influences the water contact angles and their hysteresis of low-surface energy materials. Thin films of fluorine based block co-polymer itself forms nano-hemispheres ( similar to lotus leaf) at and above 100 degrees C favoring an increase in the water contact angle from 122 degrees (25 degrees C) to 138 degrees (400 degrees C). The structural, optical, mechanical and hydrophobic properties of fluorine based block co-polymer are also discussed. By applying nanolayered (5 nm) fluorine-based block co-polymer film on a vertically aligned carbon nanotubes (CNT) morphology with a certain roughness, the advancing contact angle for water on fluoro-based polymer film on a nearly atomically flat Si wafer increased from 122 degrees to 138 degrees (close to super hydrophobicity) and 150 degrees on the rough asparagus-like structure of CNT has been observed
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