Study of helical induced anisotropy in amorphous ribbons for sensor applications

Amorphous samples with helical induced anisotropy show magnetization processes that can be controlled by applying a longitudinal magnetic field simultaneously with an alternating current flowing through the sample. By varying the current amplitude and the phase difference between current and applied field, a wide range of coercivity and susceptibility values can be achieved. This work shows that the apparent coercive field and the susceptibility can be controlled in amorphous ribbons with helical anisotropy. These characteristics make these samples very suitable for their application as sensor cores, magnetic amplifiers, variable reluctance transformer cores, etc

Investigation of the Epitaxial Graphene/p-SiC Heterojunction

There has been significant research in the study of in-plane charge-carrier transport in graphene in order to understand and exploit its unique electrical properties; however, the vertical graphene–semiconductor system also presents opportunities for unique devices. In this letter, we investigate the epitaxial graphene/p-type 4H-SiC system to better understand this vertical heterojunction. The I–V behavior does not demonstrate thermionic emission properties that are indicative of a Schottky barrier but rather demonstrates characteristics of a semiconductor heterojunction. This is confirmed by the fitting of the temperature-dependent I–V curves to classical heterojunction equations and the observation of band-edge electroluminescence in SiC.

Vertical conduction properties of few-layer epitaxial graphene / n-type 4H-SiC heterojunctions at cryogenic temperatures

Vertical diodes of epitaxial graphene on n 4H-SiC were investigated. The graphene Raman spectraexhibited a higher intensity in the G-line than the 2D-line, indicative of a few-layer graphene film.Rectifying properties improved at low temperatures as the reverse leakage decreased over six ordersof magnitude without freeze-out in either material. Carrier concentration of 10 16 cm 3in the SiCremained stable down to 15 K, while accumulation charge decreased and depletion width increasedin forward bias. The low barrier height of 0.08 eV and absence of recombination-induced emissionindicated majority carrier field emission as the dominant conduction mechanism.

Nanotechnology for high frequency communications: nitrides and graphene

The achievement of higher frequencies (HF) and the reduction of energy consumption, to improve sensing, communication and computation, involve the continued scaling down to the nanometer level. This scaling is enabled by of innovative device designs, improved processing technologies and assessment tools, and new material structures. In this work, we have used all these factors to demonstrate state-of-the-art HF devices in two materials with quite different electronic properties: wide semiconductor bandgap III-nitrides for resonators and power amplifiers; and graphene, a zero bandgap material expected to revolutionize low noise and HF flexible electronics. Some issues faced during their development will be discussed during the talk.

Graphene for energy storage

Due to its excellent mechanical, termal, optical and electrical properties, graphene has recently attracted increasing attention. It provides a huge surface area (2630m2 g-1) and high electrical conductivity, making it an attractive material for applications in energy-storage systems.

Electrical model for characterizing CVD graphene

Due to its extremely small thickness (0.35 nm), graphene is an intrinsic 2D nanomaterial. As in many other nanomaterials, its unique properties are derived from its exceptional dimensions. One of these properties is its linear dispersion equation that implies charge carriers with extraordinary high mobility. Therefore, the electronic properties of the material can lead to a big improvement in the performance of known electronic devices, or even result in novel devices for a post-silicon era.

Method for electrical evaluation of graphene using a GFET structure

n this work, we explain a method to characterize graphene using electrical measurements in graphene field-effect transistors (GFET) devices. Our goal is to obtain the material electronic properties from the output characteristics of one GFET device. For the previous purpose, we will need to apply a physical model that allows us to correlate the electronic behavior of a GFET with the material properties.

Graphene foam functionalized with electrodeposited nickel hydroxide for energy applications

The need of new systems for the storage and conversion of renewable energy sources is fueling the research in supercapacitors. In this work, we propose a low temperature route for the synthesis of electrodes for these supercapacitors: electrodeposition of a transition metal hydroxide–Ni(OH)2 on a graphene foam. This electrode combines the superior mechanical and electrical properties of graphene, the large specific surface area of the foam and the large pseudocapacitance of Ni(OH)2. We report a specific capacitance up to 900 F/g as well as specific power and energy comparable to active carbon electrodes. These electrodes are potential candidates for their use in energy applications.

Coupling light into graphene plasmons with the help of surface acoustic waves

We propose a scheme for coupling laser light into graphene plasmons with the help of electrically generated surface acoustic waves. The surface acoustic wave forms a diffraction grating which allows us to excite the long lived phononlike branch of the hybridized graphene plasmon-phonon dispersion with infrared laser light. Our approach avoids patterning the graphene sheet, does not rely on complicated optical near-field techniques, and allows us to electrically switch the coupling between far-field radiation and propagating graphene plasmons.

Determination of a refractive index and an extinction coefficient of standard production of CVD-graphene

The refractive index and extinction coefficient of chemical vapour deposition grown graphene are determined by ellipsometry analysis. Graphene films were grown on copper substrates and transferred as both monolayers and bilayers onto SiO2/Si substrates by using standard manufacturing procedures. The chemical nature and thickness of residual debris formed after the transfer process were elucidated using photoelectron spectroscopy. The real layered structure so deduced has been used instead of the nominal one as the input in the ellipsometry analysis of monolayer and bilayer graphene, transferred onto both native and thermal silicon oxide. The effect of these contamination layers on the optical properties of the stacked structure is noticeable both in the visible and the ultraviolet spectral regions, thus masking the graphene optical response. Finally, the use of heat treatment under a nitrogen atmosphere of the graphene-based stacked structures, as a method to reduce the water content of the sample, and its effect on the optical response of both graphene and the residual debris layer are presented. The Lorentz-Drude model proposed for the optical response of graphene fits fairly well the experimental ellipsometric data for all the analysed graphene-based stacked structures.

Quantifying pulsed laser induced damage to grapheme

As an emerging optical material, graphene’s ultrafast dynamics are often probed using pulsed lasers yet the region in which optical damage takes place is largely uncharted. Here, femtosecond laser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged area has a linear correlation with the optical fluence. These results demonstrate local modification of sp2-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm2, an order-of-magnitude lower than measured and theoretical ablation thresholds.

An investigation into hot-spots in two large grid-connected PV plants

This paper details an investigation into the appearance of hot-spots in two large grid-connected photovoltaics (PV) plants, which were detected after the visual inspection of trackers whose energy output was decreasing at anomalous rate. Detected hot-spots appeared not only in the solar cells but also in resistive solder bonds (RSB) between cells and contact ribbons. Both types cause similar irreversible damage to the PV modules, but the latter are the main responsible for the detected decrease in energy output, which was confirmed in an experimental testing campaign. The results of this investigation, for example, how hot-spots were detected or their impact on the output power of PV modules, may be of interest for the routine maintenance of large grid-connected PV plants.

Estudio de las propiedades del grafeno y sus posibilidades

El objetivo principal de este proyecto es el de estudiar mediante elipsometría las propiedades ópticas de una capa de grafeno sobre varios sustratos, y cómo ésta puede alterar los parámetros ópticos del material sobre el que reposa. Partiendo de muestras de cobre y silicio, se estudiará cómo pueden ser modificadas sus propiedades con tan sólo depositar sobre ellas una capa de grafeno cuyo espesor es el de un átomo. Se usará un elipsómetro de alta precisión proporcionado por el INTA para analizar todas las alteraciones respecto al material original sin grafeno. ABSTRACT The main purpose of the project is to study the optical properties of a layer of graphene on various substrates and how it can change the optical parameters of the material on which it rests, using ellipsometry. Starting from substrates of copper and silicon, we will study how their properties can be modified, by coating them with a layer of graphene, whose thickness is of one atom. For analyzing the changes with respect to the materials without graphene, an ellipsometer supply by INTA was employed.

Polyaniline-coated carbon papers for supercapacitor electrodes

Graphene and carbon nanotubes are promising materials for supercapacitor electrodes because of their high specific surface area and excellent electrical, thermal, and mechanical properties. However, these materials suffer from a high manufacturing cost and some aggregation of graphene layers or the presence of toxic residual metallic impurities of carbon nanotubes.