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

Wear behaviour of WC plasma sprayed coatings wi th micro and nanostructured powders

El objetivo de este trabajo es estudiar el comportamiento a desgaste de distintos recubrimientos de WC sobre acero inoxidable mediante proyección por plasma atmosférico. Se proyectan dos tipos de polvos comerciales con base cobalto (12 %) y níquel (10 %), con el objeto de analizar la influencia de la matriz e incluso del espesor del recubrimiento. Los recubrimientos obtenidos se caracterizan microestructuralmente por microscopía electrónica de barrido y difracción de rayos X. La caracterización tribológica de los recubrimientos se realiza mediante ensayos pin-on-disc contra bolas cerámicas de alúmina (2.400 HV) y nitruro de silicio (1.600 HV), sin lubricación, obteniéndose las tasas de desgaste y la evolución del coeficiente de rozamiento. Las pistas de desgaste y los residuos generados se caracterizaron mediante Microscopía Electrónica de Barrido, MEB. Los resultados muestran diferentes mecanismos de desgaste en cada par de material ensayado en función de la matriz y de la naturaleza de la bola empleada en el ensayo, encontrándose mayores tasas de desgaste con bola de nitruro de silicio. En una segunda fase, se obtienen recubrimientos, con dos polvos base cobalto cuyos tamaños de partícula son micrométrico y nanométrico, respectivamente, con el objetivo de estudiar la influencia del tamaño de partícula inicial sobre las propiedades a desgaste del recubrimiento. Los resultados obtenidos ponen de manifiesto una mayor resistencia al desgaste de los recubrimientos obtenidos con polvos nanoestructurados, bajo condiciones de carga elevadas, mientras que para cargas bajas ambos recubrimientos presentan un comportamiento similar a pesar de las diferencias microestructurales apreciadasThe aim of the present work is the study of wear behaviour of different WC coatings deposited on stainless steel substrate by means of atmospheric plasma spraying (APS). Two types of WC commercial powders, with different metal binder (12% Cobalt and 10% Nickel) have been deposited in order to analyse the influence of the metal matrix and thickness of the coating in tribological properties.The microstructure of the depositions was characterized using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). On the other hand, tribology characterization of the coatings was made by pin-on-disk wear tests against alumina (2400HV) and silicon nitride (1600HV) ceramic balls, without lubrication. Wear rates and friction coefficient evolution have been calculated. Finally, wear tracks and wear debris have been analysed with the help of SEM.The results of each pair of tested materials show different mechanisms of wear related to the nature of the ball that has been used, obtaining higher wear rates with silicone nitride ball..In a second phase of the study, in order to examine the influence of the initial particle size on the wear properties of the coatings, cobalt based coatings have been analysed with different initial particle size (micrometric and nanometric particles).Results show that nanostructured coatings have higher wear resistance than microstrutured ones for high loads. However for low loads, behaviour is similar in spite of the microstructural differences appreciate

Extraordinary linear dynamic range in laser-defined functionalized graphene photodetectors

Graphene-based photodetectors have demonstrated mechanical flexibility, large operating bandwidth, and broadband spectral response. However, their linear dynamic range (LDR) is limited by graphene's intrinsichot-carrier dynamics, which causes deviation from a linear photoresponse at low incident powers. At the same time, multiplication of hot carriers causes the photoactive region to be smeared over distances of a few micro-meters, limiting the use of graphene in high-resolution applications. We present a novel method for engineer-ing photoactive junctions in FeCl3-intercalated graphene using laser irradiation. Photocurrent measured at these planar junctions shows an extraordinary linear response with an LDR value at least 4500 times larger than that of other graphene devices (44 dB) while maintaining high stability against environmental contamination without the need for encapsulation. The observed photoresponse is purely photovoltaic, demonstrating complete quenching of hot-carrier effects. These results pave the way toward the design of ultrathin photode-tectors with unprecedented LDR for high-definition imaging and sensing.Comment: 44 pages, includes supplementar

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

Ammonia levels in different kinds of sampling sites in the central Iberian Peninsula

Ponencia presentada en:2nd Iberian Meeting on Aerosol Science and Technology (RICTA 2014) celebrado en Tarragona del 7 al 9 de julio de 2014.Ammonia is the Secondary Inorganic Aerosol (SIC) gaseous precursor which has been studied to a lesser extent in the Madrid Metropolitan Area up to date. A study conducted in the city of Madrid with the aim of characterizing levels of ammonia took place in 2011. These campaigns formed part of a larger study conducted in 6 Spanish cities. A time series of weekly integrated ammonia measurements available at an EMEP rural site (Campisábalos) has been used to obtain information on the ammonia rural background in the region. The results point to traffic and waste treatment plants as the main ammonia sources in Madrid. Relevant seasonal differences have not been observed in the Metropolitan Area. The explanation can be related to the fall in the rural background levels during July 2011, which might conceal urban summer emission increases observed in other cities

Congreso online: nueva herramienta para fomentar el aprendizaje

Los congresos científicos son una herramienta valiosa en el aprendizaje para estudiantes de tercer ciclo. Sin embargo, no son aprovechados al máximo con esta finalidad, puesto que las intervenciones por parte de los estudiantes, en cuanto a plantear cuestiones se refiere, son prácticamente nulas. Con el objetivo de fomentar la participación de los estudiantes de tercer ciclo en los congresos científicos, se presenta una propuesta de congreso online para estudiantes de doctorado en el programa interuniversitario `Electroquímica. Ciencia y Tecnología`, empleando la herramienta Moodle. Este congreso consiste en dar a conocer, de forma visible y con formato de pósters, comunicaciones científicas de los estudiantes, quienes deben hacer preguntas acerca de las mismas y responder a las realizadas sobre su contribución. Además, y siempre con la finalidad de fomentar la participación en forma de preguntas y discusiones científicas, se otorgarán premios tales como al estudiante más participativo y al mejor póster, para lo que se evaluará la defensa del póster por parte del estudiante

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.Comment: 239 pages, 11 figures, white paper from the LISA Consortium Waveform Working Group, invited for submission to Living Reviews in Relativity, updated with comments from communit

Phonon-Polaritonic Bowtie Nanoantennas: Controlling Infrared Thermal Radiation at the Nanoscale

A conventional thermal emitter exhibits a broad emission spectrum with a peak wavelength depending upon the operation temperature. Recently, narrowband thermal emission was realized with periodic gratings or single microstructures of polar crystals supporting distinct optical modes. Here, we exploit the coupling of adjacent phonon-polaritonic nanostructures, demonstrating experimentally that the nanometer-scale gaps can control the thermal emission frequency while retaining emission line widths as narrow as 10 cm^–1. This was achieved by using deeply subdiffractional bowtie-shaped silicon carbide nanoantennas. Infrared far-field reflectance spectroscopy, near-field optical nanoimaging, and full-wave electromagnetic simulations were employed to prove that the thermal emission originates from strongly localized surface phonon-polariton resonances of nanoantenna structures. The observed narrow emission line widths and exceptionally small modal volumes provide new opportunities for the user-design of near- and far-field radiation patterns for advancements in infrared spectroscopy, sensing, signaling, communications, coherent thermal emission, and infrared photodetection

Non-lithographic SERS substrates: tailoring surface chemistry for Au nanoparticle cluster assembly.

Near-field plasmonic coupling and local field enhancement in metal nanoarchitectures, such as arrangements of nanoparticle clusters, have application in many technologies from medical diagnostics, solar cells, to sensors. Although nanoparticle-based cluster assemblies have exhibited signal enhancements in surface-enhanced Raman scattering (SERS) sensors, it is challenging to achieve high reproducibility in SERS response using low-cost fabrication methods. Here an innovative method is developed for fabricating self-organized clusters of metal nanoparticles on diblock copolymer thin films as SERS-active structures. Monodisperse, colloidal gold nanoparticles are attached via a crosslinking reaction on self-organized chemically functionalized poly(methyl methacrylate) domains on polystyrene-block-poly(methyl methacrylate) templates. Thereby nanoparticle clusters with sub-10-nanometer interparticle spacing are achieved. Varying the molar concentration of functional chemical groups and crosslinking agent during the assembly process is found to affect the agglomeration of Au nanoparticles into clusters. Samples with a high surface coverage of nanoparticle cluster assemblies yield relative enhancement factors on the order of 10⁹ while simultaneously producing uniform signal enhancements in point-to-point measurements across each sample. High enhancement factors are associated with the narrow gap between nanoparticles assembled in clusters in full-wave electromagnetic simulations. Reusability for small-molecule detection is also demonstrated. Thus it is shown that the combination of high signal enhancement and reproducibility is achievable using a completely non-lithographic fabrication process, thereby producing SERS substrates having high performance at low cost