On the mechanisms of precipitation of graphene on nickel thin films

Growth on transition metal substrates is becoming a method of choice to prepare large-area graphene foils. In the case of nickel, where carbon has a significant solubility, such a growth process includes at least two elementary steps: (1) carbon dissolution into the metal, and (2) graphene precipitation at the surface. Here, we dissolve calibrated amounts of carbon in nickel films, using carbon ion implantation, and annealing at 725 \circ or 900 \circ. We then use transmission electron microscopy to analyse the precipitation process in detail: the latter appears to imply carbon diffusion over large distances and at least two distinct microscopic mechanisms

Investigation of the reactivity of AlCl3 and CoCl2 toward molten alkali-metal nitrates in order to synthesize CoAl2O4

Cobalt aluminate CoAl2O4 powder, constituted of nano-sized crystallites, is prepared, involving the reactivity of AlCl3 and CoCl2 with molten alkali-metal nitrates. The reaction at 450 °C for 2 h leads to a mixture of spinel oxide Co3O4 and amorphous γ-Al2O3. It is transformed into the spinel oxide CoAl2O4 by heating at 1000 °C. The powders are mainly characterized by XRD, FTIR, ICP, electron microscopy and diffraction, X-EDS and diffuse reflection. Their properties are compared to those of powders obtained by solid state reactions of a mechanical mixture of chlorides or oxides submitted to the same thermal treatment

Graphene growth directly on functional substrate

Graphene is perhaps the most promising material ever discovered for microelectronics applications, but its preparation includes either high-temperature processing or film transfer, and sometimes both of them, which forbids for the moment its introduction into fabrication lines. In this communication we report a synthesis route involving exposure of nickel thin films deposited on silicon oxide to a mixture of methane and hydrogen activated by DC plasma at 450°C. In addition of the awaited graphene film formed at the surface of catalyst layer, we observed the formation of a second graphene film at the catalyst/silicon oxide interface. To our knowledge, no other team have yet reported graphene synthesis directly on a dielectric substrate at low temperature. With the idea of increasing the graphene structural quality, we studied the effect of additional post growth high temperature annealing. The films synthesized were characterized using Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM)

New thermodynamic data for CoTiO3, NiTiO3 and CoCO3 based on low-temperature calorimetric measurements

The low-temperature heat capacities of nickel titanate (NiTiO3), cobalt titanate (CoTiO3), and cobalt carbonate (CoCO3) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO3 and 26 K for NiTiO3. From our data we calculate standard molar entropies (298.15 K) for NiTiO3 of 90.9 ± 0.7 J mol-1 K-1 and for CoTiO3 of 94.4 ± 0.8 J mol-1 K-1. For CoCO3, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO3 of 88.9 ± 0.7 J mol-1 K-1

TCO materials for gas sensors : stakes and challenges

International audienceThe range of major applications of transparent conducting oxides (TCOs) continues to expand, thus generating a growing demand for new materials with lower resistivity and higher transparency over extended wavelength ranges. In addition, p-type TCOs are opening new horizons for highperformance devices based on p-n junctions. Among the most commonly used TCO materials are tin oxide (SnO2), indium oxide (In2O3), indium tin oxide (ITO), zinc oxide (ZnO). But design and synthesis of improved TCO materials leading to a marked increase in conductivity and robustness remain highly desirable while a more detailed understanding of the conductivity mechanisms is critical to further improvement. This lecture will review new developments in TCO materials to be used in high-performance and cost-effective gas sensors. The stakes in the sensor market and the current scientific and technological challenges to be taken up will be discussed

NOx detection by semiconductor Tin oxide nanoparticles : FTIR analysis of transducing mechanisms

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