Christophe Tenailleau

Synthesis of large-area and aligned copper oxide nanowires from copper thin film on silicon substrate

Large-area and aligned copper oxide nanowires have been synthesized by thermal annealing of copper thin films deposited onto silicon substrate. The effects of the film deposition method, annealing temperature, film thickness, annealing gas, and patterning by photolithography are systematically investigated. Long and aligned nanowires can only be formed within a narrow temperature range from 400 to 500°C. Electroplated copper film is favourable for the nanowire growth, compared to that deposited by thermal evaporation. Annealing copper thin film in static air produces large-area, uniform, but not well vertically aligned nanowires along the thin film surface. Annealing copper thin film under a N2/O2 gas flow generates vertically aligned, but not very uniform nanowires on large areas. Patterning copper thin film by photolithography helps to synthesize large-area, uniform, and vertically aligned nanowires along the film surface. The copper thin film is converted into bicrystal CuO nanowires, Cu2O film, and also perhaps some CuO film after the thermal treatment in static air. Only CuO in the form of bicrystal nanowires and thin film is observed after the copper thin film is annealed under a N2/O2 gas flow.

Development of a nano-Al∕CuO based energetic material on silicon substrate

Nanoenergetic materials (nEMs) have improved performances compared to their bulk counterpart or microcounterpart. The authors propose an approach to synthesize an Al∕CuO based nEM that has several advantages over previous investigations such as enhanced contact, reduced impurities and Al oxidation, tailored dimensions, and easier integration into microsystem. CuO nanowires are synthesized by thermally annealing Cu film deposited onto silicon. Nano-Al is integrated with the nanowires to realize an Al∕CuO based nEM. The synthesized nEM is characterized by scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction, differential thermal analysis, and differential scanning calorimetry.

Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.

Interfacial Chemistry in Al/CuO Reactive Nanomaterial and Its Role in Exothermic Reaction

Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and alumina/Al rather than the thickness of the alumina layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.

Understanding the Fragmentation Pattern of Marine Plastic Debris

The global estimation of microplastic afloat in the ocean is only approximately 1% of annual global plastic inputs. This reflects fundamental knowledge gaps in the transformation, fragmentation, and fates of microplastics in the ocean. In order to better understand microplastic fragmentation we proceeded to a thorough physicochemical characterization of samples collected from the North Artlantic subtropical gyre during the sea campaign Expedition seventh Continent in May 2014. The results were confronted with a mathematical approach. The introduction of mass distribution in opposition to the size distribution commonly proposed in this area clarify the fragmentation pattern. The mathematical analysis of the mass distribution points out a lack of debris with mass lighter than 1 mg. Characterization by means of microscopy, microtomography, and infrared microscopy gives a better understanding of the behavior of microplastic at sea. Flat pieces of debris (2 to 5 mm in length) typically have one face that is more photodegraded (due to exposure to the sun) and the other with more biofilm, suggesting that they float in a preferred orientation. Smaller debris, with a cubic shape (below 2 mm), seems to roll at sea. All faces are evenly photodegraded and they are less colonized. The breakpoint in the mathematical model and the experimental observation around 2 mm leads to the conclusion that there is a discontinuity in the rate of fragmentation: we hypothesized that the smaller microplastics, the cubic ones mostly, are fragmented much faster than the parallelepipeds.

Origin of colossal permittivity in BaTiO3 via broadband dielectric spectroscopy

Barium titanate (BT) ceramics with Ba/Ti ratios of 0.95 and 1.00 were synthesized using spark plasma sintering (SPS) technique. Dielectric spectroscopy (frequency range from 40 Hz to 1 MHz and temperature range from 300 K to 30 K) was performed on those ceramics (SPS BT). SPS BT showed extremely high permittivity up to ∼105, which can be referred to as colossal permittivity, with relatively low dielectric loss of ∼0.05. Data analyses following Debye relaxation and universal dielectric response models indicate that the origin of colossal permittivity in BT ceramics is the result of a hopping polaron within semiconducting grains in combination with interfacial polarization at the insulating grain boundary. Furthermore, the contributions of each polarization mechanism to the colossal permittivity in SPS BT, such as a hopping polarization, internal barrier layer capacitance effect, and electrode effect, were estimated.

Transformation of pentlandite to violarite under mild hydrothermal conditions

Abstract The transformation of pentlandite, (Ni,Fe)9S8, to violarite, (Ni,Fe)3S4, has been investigated under mild hydrothermal conditions, at constant values of pH (range 3 to 5) controlled by the acetic acid/sodium acetate buffer. At 80 °C, 20(4) wt% of the pentlandite transforms to violarite in 33 days; with the addition of small amounts of Fe3+(CH3COO)2(OH) and H2S the reaction reaches 40(4) wt% completion in this time. At 120 °C and a pressure of 3.5 bars the reaction is complete in 3 days at pH 3.9. Electron backscatter diffraction and backscattered electron imaging reveal that the reaction textures are typical of a coupled dissolution-reprecipitation reaction, rather than a solid state electrolytic process as has been previously reported. The gap between the dissolution front and the precipitation front of violarite is less than 400 nm. The violarite produced by these hydrothermal transformations is texturally similar to supergene violarite, being fine grained, porous and finely cracked.

Enhancing the Reactivity of Al/CuO Nanolaminates by Cu Incorporation at the Interfaces

In situ deposition of a thin (∼5 nm) layer of copper between Al and CuO layers is shown to increase the overall nanolaminate material reactivity. A combination of transmission electron microscopy imaging, in situ infrared spectroscopy, low energy ion scattering measurements, and first-principles calculations reveals that copper spontaneously diffuses into aluminum layers (substantially less in CuO layers). The formation of an interfacial Al:Cu alloy with melting temperature lower than pure Al metal is responsible for the enhanced reactivity, opening a route to controlling the stochiometry of the aluminum layer and increasing the reactivity of the nanoenergetic multilayer systems in general.

The crystal chemistry of Fe-bearing sphalerites: An infrared spectroscopic study

Abstract Iron substitution into sphalerite, ZnS, has been studied systematically by infrared spectroscopy. A range of natural and synthetic compositions, (Zn1-xFex)S, 0 ≤ x ≤ 0.24, were examined. The IR spectrum of pure ZnS contains a single strong absorption band at 320 cm-1. With addition of FeS, the spectra become broader and shoulders appear. For compositions ≥9 mol% FeS, a splitting of the main peak occurs, and the spectra show two absorption maxima at approximately 300 and 315 cm-1, respectively. The observation of such extra features does not correspond to the usual behavior observed in other ternary mixed crystals, where either one-, two-, or mixed-mode behavior is observed. The spectra can be deconvoluted into up to three peaks, main Peaks A and B at around 300 and 315 cm-1, respectively, and a shoulder at around 330 cm-1 (Peak C). The positions and area of the peaks do not change significantly with increasing Fe content. The peak at 315 cm-1 is the main absorption peak of the host ZnS structure, and the peak at 300 cm-1 is an impurity induced mode. An effective linewidth parameter Δcorr was determined by autocorrelation analysis for each spectrum, but there are no obvious trends in the values of Δcorr that can be interpreted in terms of an inhomogeneous distribution of Fe within the sphalerite structure.

Thermal expansion of troilite and pyrrhotite determined by in situ cooling (873 to 373 K) neutron powder diffraction measurements

Abstract The thermal expansion coefficients for natural troilite, FeS, Ni-rich pyrrhotite, Fe0.84Ni0.11S, and Ni-poor pyrrhotite, Fe0.87Ni0.02S, were measured during cooling by in situ neutron powder diffraction over the temperature range 873-373 K. Between 873 and 573 K, the mean thermal expansion coefficients for the three compositions are 7.4(3) × 10-5 {FeS}, 8.0(4) × 10-5 {Fe0.84Ni0.11S} and 8.5(4) × 10-5 K-1 {Fe0.87Ni0.02S}. Below 573 down to 373 K, the first two increase considerably to 14.1(7) × 10-5 {FeS} and 9.3(5) × 10-5 {Fe0.84Ni0.11S} while the latter sample shows no significant variation, 8.4(5) × 10-5 K-1. Below 573 K, the thermal expansion is highly anisotropic, with ∆a/100 K-1 ranging from 0.89(9)% {FeS} to 0.48(12)% {Fe0.87Ni0.02S} while ∆c/100 K-1 ranges from -0.39(11)% {FeS} to -0.13(2)% {Fe0.87Ni0.02S}. Upon cooling through 573 K, troilite and pyrrhotite undergo a transition where the FeS6 octahedra distort and in the case of pyrrhotite, cation-vacancy clustering occurs. The thermal expansion coefficients are bigger for low cation-vacancy concentrations and decrease as the pyrrhotites become less stoichiometric. This indicates that the thermal expansion in these minerals is damped by vacancy ordering or clustering. The thermal expansion coefficients for troilite and pyrrhotite are amongst the largest reported for sulphide minerals and their role in the formation of ore textures is discussed briefly.