49 research outputs found

    Synthesis of Ternary Borocarbonitrides by High Temperature Pyrolysis of Ethane 1,2-Diamineborane

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    Ethane 1,2-diamineborane (EDAB) is an alkyl-containing amine-borane adduct with improved hydrogen desorption properties as compared to ammonia borane. In this work, it is reported the high temperature thermolytic decomposition of EDAB. Thermolysis of EDAB has been investigated by concomitant thermogravimetry-differential thermal analysis-mass spectrometry experiments. EDAB shows up to four H2 desorption events below 1000 °C. Small fractions of CH4, C2H4 and CO/CO2 are also observed at moderate-high temperatures. The solid-state thermolysis product has been characterized by means of different structural and chemical methods, such as X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Elemental analysis, and X-ray photoelectron spectroscopy (XPS). The obtained results indicate the formation of a ternary borocarbonitride compound with a poorly-crystalline graphitic-like structure. By contrast, XPS measurements show that the surface is rich in carbon and nitrogen oxides, which is quite different to the bulk of the materialSome authors (Fabrice Leardini, Lorenzo Massimi, Maria Grazia Betti and Carlo Mariani) also thank Sapienza Università di Roma for financial support under “Progetti di Ateneo”, and the Italian Ministry of Education and Research (MIUR) for the PRIN grant “GRAF” n. 20105ZZTS

    Electronic structure of copper nitrides as a function of nitrogen content

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    he nitrogen content dependence of the electronic properties for copper nitride thin films with an atomic percentage of nitrogen ranging from 26 ± 2 to 33 ± 2 have been studied by means of optical (spectroscopic ellipsometry), thermoelectric (Seebeck), and electrical resistivity measurements. The optical spectra are consistent with direct optical transitions corresponding to the stoichiometric semiconductor Cu3N plus a free-carrier contribution, essentially independent of temperature, which can be tuned in accordance with the N-excess. Deviation of the N content from stoichiometry drives to significant decreases from − 5 to − 50 μV/K in the Seebeck coefficient and to large enhancements, from 10− 3 up to 10 Ω cm, in the electrical resistivity. Band structure and density of states calculations have been carried out on the basis of the density functional theory to account for the experimental results

    Dielectrophoretic assembly of liquid-phase-exfoliated TiS3 nanoribbons for photodetecting applications

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    Liquid-phase exfoliation is a technique capable of producing large quantities of two-dimensional materials in suspension. Despite many efforts in the optimization of the exfoliation process itself, not much has been done towards the integration of liquid-phase-exfoliated materials in working solid-state devices. In this article, we use dielectrophoresis to direct the assembly of liquid-phase-exfoliated TiS3 nanoribbons between two gold electrodes to produce photodetectors working in the visible region. Through electrical and optical measurements we characterize the responsivity of the device and we find values as large as 3.8 mA W-1, which are more than one order of magnitude higher compared to state-of-the-art devices based on liquid-phase-exfoliated two-dimensional materials assembled by drop-casting or ink-jet methods

    Tunable Photodetectors via In Situ Thermal Conversion of TiS3 to TiO2

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    In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS3), a layered semicon-ductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectron-ic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of indi-vidual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetec-tors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS3 devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO2-xSx) when in-creasing the amount of oxygen and reducing the amount of sulfur

    Matching times: Trying to improve the correlation between heavy metal levels in mosses and bulk deposition

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    The relationship between the concentrations of metals in moss tissues and atmospheric deposition is highly complex, resulting in a general lack of correlations between these two matrices. Here, we tried to improve the significance of the moss-bulk deposition (BD) relationship by eliminating the mismatch between the time that the moss tissue selected for analysis is exposed to atmospheric deposition, and the time during which BD is collected. For this, we analysed the concentrations of Cd, Hg and Pb in new grown tissue of Pseudoscleropodium purum and BD collected monthly, for one year, in 21 sampling sites (SS) under different degrees of pollution. Additionally, we assessed how different moss tissues, including native moss (green parts and new grown tissues of P. purum) and moss transplants of Sphagnum denticulatum, reflect BD to find out which moss tissues provide a better estimate of the atmospheric deposition of heavy metals. First of all, our results showed that eliminating the mismatch between native moss exposure time and BD collection period is not enough to improve their correlation. Environmental variation emerged as the main driver of tissue content variation altering the moss-BD relationship unpredictably. Secondly, native P. purum represents BD values better than devitalized transplants by displaying a greater number of significant correlations with BD. Specifically, green parts of P. purum generally represent better BD than new grown tissues. Overall, we conclude that neither native mosses nor transplants are good estimators of atmospheric heavy metal deposition rates. However, they are good qualitative indicators of the atmospheric deposition, by allowing us to differentiate SS subject to a wide range of pollution levels. Additionally, green parts of P. purum, and likely of other mosses with similar growth forms, should be used in passive biomonitoring studies to make results from different studies comparable.Peer reviewe

    Simulation and design of a three-stage metal hydride hydrogen compressor based on experimental thermodynamic data

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    International audienceA semi-empirical method was developed to design a three stage Metal Hydride Hydrogen Compressor (MHHC) through the determination of thermodynamic properties of several hydrides. As a first step, three AB2-type alloys that satisfy operation conditions were selected from published thermodynamic data entailing over 200 single plateau hydrides. These alloys were synthetized by arc melting and characterized by X-Ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM) and Energy Dispersion X-ray spectroscopy (EDX). Absorption and desorption Pressure-composition-Isotherms (P-c-I) were determined between 23 and 80 °C to characterize their thermodynamic properties. Subsequently, an algorithm that uses these experimental data and a real equation of state for gaseous H2 was implemented to simulate the volume, alloy mass, pressure and temperature of operation for each compressor stage, while optimizing the compression ratio and total number of compressed H2 moles. Optimal desorption temperatures for the three stages were identified within the range of 110–132 °C. A system compression ratio (CR) of 92 was achieved. The number of H2 moles compressed, the alloy mass and volume of each stage depend linearly on the volume of the external tank in which the hydrogen is delivered