Optical Imaging Using Binary Sensors

This paper addresses the problem of reconstructing an image from 1-bit-quantized measurements, considering a simple but nonconventional optical acquisition model. Following a compressed-sensing design, a known pseudo-random phase-shifting mask is introduced at the aperture of the optical system. The associated reconstruction algorithm is tailored to this mask. Our results demonstrate the feasibility of the whole approach for reconstructing grayscale images

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation

Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development. Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to ¿ 350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at.%. Nitrogen content increase induces a higher sp2 character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor.This work is produced with the financial support of the Future Program Lyon Saint-Etienne (PALSE) from the University of Lyon (ANR-11-IDEX-0007), under the “Investissements d'Avenir” program managed by the National Agency Research (ANR)

Nano-Architecture of nitrogen-doped graphene films synthesized from a solid CN source

New synthesis routes to tailor graphene properties by controlling the concentration and chemical configuration of dopants show great promise. Herein we report the direct reproducible synthesis of 2-3% nitrogen-doped ‘few-layer’ graphene from a solid state nitrogen carbide a-C:N source synthesized by femtosecond pulsed laser ablation. Analytical investigations, including synchrotron facilities, made it possible to identify the configuration and chemistry of the nitrogen-doped graphene films. Auger mapping successfully quantified the 2D distribution of the number of graphene layers over the surface, and hence offers a new original way to probe the architecture of graphene sheets. The films mainly consist in a Bernal ABA stacking three-layer architecture, with a layer number distribution ranging from 2 to 6. Nitrogen doping affects the charge carrier distribution but has no significant effects on the number of lattice defects or disorders, compared to undoped graphene synthetized in similar conditions. Pyridinic, quaternary and pyrrolic nitrogen are the dominant chemical configurations, pyridinic N being preponderant at the scale of the film architecture. This work opens highly promising perspectives for the development of self-organized nitrogen-doped graphene materials, as synthetized from solid carbon nitride, with various functionalities, and for the characterization of 2D materials using a significant new methodology

ÉCARTS A LA LOI DE MATTHIESSEN ET STRUCTURE ÉLECTRONIQUE DES IMPURETÉS DE COBALT DANS LE CUIVRE

Nous avons étudié la susceptibilité magnétique et la résistance électrique d'alliages dilués de Co dans le Cu (concentration c < 1 %° at.), dans le but de préciser la structure électronique des impuretés isolées. Nous montrons que les impuretés isolées de Co sont presque magnétiques avec une température de fluctuation de spin de 600 °K et que la résistivité électron-phonon est modifiée par suite de la variation rapide du temps de relaxation avec l'énergie ; nous mettons en évidence une nouvelle contribution à l'écart à la loi de Matthiessen.The magnetic susceptibility and electrical resistivity of dilute alloys of Co in Cu (concentration less than 1 at. %°) have been studied. The purpose is to specify the electronic structure of the isolated impurities. The results show that (1) the Co impurities are nearly magnetic with a spin fluctuation temperature of 600 °K (2) the electron-phonon resistivity is modified from the rapid variation of the relaxation time with energy

Comparative Raman study of graphene growth from solid carbon source on Si(100) and SiO2 substrates by combining pulsed laser deposition and rapid thermal annealing

International audienceThis study reports the comparative investigation of graphene films prepared on Si (100) and SiO2 by combining pulsed laser deposition and rapid thermal annealing using Ni catalyst. The effect of substrate and growth temperatures (600-1000°C) on the formation of graphene films was investigated by Raman spectroscopy, mapping and scanning electron microscopy (SEM). It was found that graphene films formed on Si (100) is multilayered with the formation of various nickel silicides depending on the growth temperature, while graphene films prepared on SiO2 are predominant bi- and trilayered graphene with no nickel silicide formation. The analysis of the Raman D, G and 2D peaks intensities and positions as a function of the growth temperature showed a complete opposite evolution between Si (100) and SiO2 substrates. These findings contribute to a better understanding of the combination between the nature of the substrate and the growth temperature, when growing graphene films from solid carbon source with nickel catalyst on both Si(100) and SiO2 substrates. Such a good comprehension of the substrate impact is vital for potential applications and device fabrication of graphene

Pulsed laser co-deposition of carbon and boron for boron-doped graphene synthesis

International audienceThe introduction of dopants, such as boron, into the graphene network, is essential for many applications (electrochemistry, sensors, photovoltaics, catalysis, etc.). Many preparation routes have been investigated for B-doped graphene (BG) films: CVD, chemical reactions between graphene or graphene oxide with boron precursors, hydrothermal and solvothermal processes, arc discharge, high temperature sublimation of highly B-doped SiC and B4C thermal decomposition. Another way consists in pulsed laser co-ablation of C and B solid sources followed by rapid thermal heating of the B-doped carbon film deposited on a metal catalyst, to obtain BG layers. The objective is to achieve a better control of boron concentration in the films.Here, we use for the first time pulsed laser co-ablation for the synthesis of B-doped graphene layers. Amorphous a-C:B films, containing 2%at. boron, 10 nm thick, are synthetized by nanosecond pulsed laser deposition on a Ni thin film (60 nm thick) previously deposited on a SiO2 substrate. Rapid Thermal Annealing is performed at 1100°C during 2’ with a heating rate of 15°C/s and a cooling rate of 1°C/s. Raman, XPS, FEG-SEM and AFM characterizations allow to determine the nature, composition and morphology of the BG films. The results confirm the fabrication of bi-trilayers boron doped graphene films with the same boron doping level (2%at) as the starting material. Our results pave a new way for boron doped graphene synthesis using laser processing

Graphene and doped-graphene synthesis by Pulse Laser Deposition: a review

International audienceGraphene is a remarkable two-dimensional (2D) material that is of great interest to both academia and industry. Several methods are used to produce either pristine graphene or doped graphene. Among these methods, Pulse Laser Deposition (PLD) has proved to be an alternative route for producing graphene layers from amorphous carbon thin films, due to many advantages including the controlled film thickness and dopant compositions in the films [1]. The present talk will review the ability of PLD to produce graphene and doped graphene films, mainly with nitrogen or boron atoms [2]. The growth mechanism will be highlighted on the basis of XPS investigations in situ during graphene growth. The film characteristics depending on the synthesis process are discussed mainly on the basis of Raman and XPS/AES investigations. Exploration of some electrical conduction properties are emphasized. In particular, electroanalytical experiments show that functionalized electrodes with nitrogen-doped graphene from PLD exhibits excellent reversibility, close to the theoretical value of 59 mV, and very high sensitivity to hydrogen peroxide oxidation [3]. The electroanalytical results were correlated with the composition and nanoarchitecture of the N-doped graphene film identified as a few-layer defected and textured graphene film containing a balanced mixture of graphitic-N and pyrrolic-N chemical functions. The present talk will help researchers to have an overview of the interest of PLD for graphene and doped-graphene synthesis

Multiscale surface texturing of zirconium based thin film metallic glasses by femtosecond laser pulses

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Dynamics of carbon diffusion and segregation through nickel catalyst, investigated by in-situ XPS, during the growth of nitrogen-doped graphene

International audienceThe mechanisms of diffusion and segregation of carbon from a solid carbon-based film, through a nickel film catalyst, was investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy. The graphene precursor was a carbon nitride amorphous film obtained by pulse laser deposition. Changes in both surface and bulk sensitive carbon components versus annealing time was investigated at temperatures between 200 °C and 500 °C. A model of carbon diffusion/segregation through the nickel film was implemented, enabling the quantitative description of the graphene growth. Carbon diffusion through the nickel film was shown to occur at low temperatures (200–300 °C) and to induce the growth of graphene domains. The fine microstructure and high density of defects in the nickel catalyst film accelerated the transport of carbon, faster than conventional bulk diffusion. At 500 °C, bulk diffusion of carbon occurred, due to the recovering of the nickel grain microstructure. The diffusion/segregation model developed in this study can be used as a support to a better control of the growth and quality of the graphene. Our interpretations are discussed in relation to similar approaches related to graphene growth by chemical vapor deposition

Elaboration of Graphene and doped-graphene by Pulsed Laser Deposition

International audienceIn recent years, the research on graphene has received a lot of interest to both academia and industry due to its outstanding physical and chemical properties, and its potential for various applications. Due to this, several methods are used to produce either pristine graphene or doped graphene. Among these methods, Pulsed Laser Deposition (PLD) has proved to be an alternative route for producing graphene layers from amorphous carbon thin films, due to many advantages including the controlled film thickness and dopant compositions in the films [1]. The present talk will give an overview of the ability of PLD to fabricate graphene and doped graphene films, mainly with nitrogen or boron atoms [2]. The growth mechanism will be highlighted based on XPS investigations in situ during graphene growth. The graphene films characteristics depending on the substrates and the influence of synthesis process parameters such as initial amorphous carbon (a-C) thickness, laser energy and annealing temperature on the growth of graphene are discussed mainly based on Raman analysis. Investigations of electrochemistry properties of nitrogen-doped graphene synthesized by PLD are emphasized. The results show that functionalized electrodes with nitrogen-doped graphene exhibit excellent reversibility, close to the theoretical value of 59 mV, and very high sensitivity to hydrogen peroxide oxidation [3]. The present talk will help researchers to get an overview of the interest of PLD for graphene and doped-graphene synthesis.References1.Y. Bleu, F. Bourquard, T. Tite, A.-S. Loir, C. Maddi, C. Donnet, F. Garrelie, Frontier in Chemistry, 2018, 6, 572.2.C. Maddi, F. Bourquard, V. Barnier, J. Avila, M.-C. Asensio, T. Tite, C Donnet, F. Garrelie, Scientific Reports, 2018, 8, 3247.3.F. Bourquard, Y. Bleu, A.-S. Loir, B. Caja-Munoz, J. Avila, M.-C. Asensio, G. Raimondi, M. Shokouhi, I. Rassas, C. Farre, C. Chaix, V. Barnier, N. Jaffrezic-Renault, F. Garrelie, C. Donnet, Materials, 2019, 12, 666