Search results for "engineering.material"

Magnetic and Electronic Properties of Heusler Alloy Films Investigated by X-Ray Magnetic Circular Dichroism

2008

We have investigated the magnetic properties of epitaxial Heusler alloy films using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism∈dex{x-ray!magnetic circular dichroism} (XMCD) in the transmission (TM) and in the surface sensitive total electron yield (TEY) mode. We have investigated Ni_2MnGa based shape memory alloys and half-metallic Co2Cro.6Feo.4 films. Single crystalline Ni2MnGa(110)/Al2O3(1120) and Ni2MnGa(100)/MgO(100) films show a martensitic transition from a cubic high temperature phase to a martensitic low-temperature phase at 250–275 K as concluded from magnetometry and x-ray diffraction. The martensitic transition of this Heusler compound is shifted in…

Metal-support interaction and redox behavior of Pt(1 wt %)/Ce0.6Zr0.4O2

2006

The catalyst Pt(1 wt %)/Ce(0.6)Zr(0.4)O(2) is studied by CO-temperature programmed reduction (CO-TPR), isothermal oxygen storage complete capacity (OSCC), X-ray absorption spectroscopy (XAS) at the Pt L(III) edge, and in situ X-ray diffraction (in situ XRD), with the aim of elucidating the role of supported metal in CO oxidation by ceria-based three-way catalysts (TWC). The redox behavior of Pt(1 wt %)/Ce(0.6)Zr(0.4)O(2) is compared to that of bare ceria-zirconia. OSCC of redox-aged Pt/ceria-zirconia is twice that of bare ceria-zirconia, and the maximum of CO consumption occurs at a temperature about 300 K lower than redox-aged ceria-zirconia. XAS analysis allows one to evidence the formati…

Exploring wet chemistry approaches to ZnFe2O4 spinel ferrite nanoparticles with different inversion degrees: A comparative study

2019

Zinc ferrite (ZnFe2O4) spinel nanocrystals were synthesised through three different low-temperature routes, namely hydrothermal, combined miniemulsion/hydrothermal, and microwave-assisted non-aqueous sol–gel synthesis. With the aim of studying the influence of the respective approach on the structural evolution of the compounds during the synthetic process, the samples were prepared with different processing times. The resulting nanoparticles were inspected with a wide range of analytical techniques, both with regards to the local (X-ray absorption spectroscopy – XAS) and the long-range (Raman spectroscopy, X-ray diffraction – XRD) order.

2016

AbstractDetermining the manganese concentration in shells of freshwater bivalves provides a unique way to obtain information about climate and environmental changes during time-intervals that pre-date instrumental data records. This approach, however, relies on a thorough understanding of how manganese is incorporated into the shell material –a point that remained controversial so far. Here we clarify this issue, using state-of-the-art X-ray absorption and X-ray emission spectroscopy in combination with band structure calculations. We verify that in the shells of all studied species manganese is incorporated as high-spin Mn2+, i.e. manganese always has the same valence as calcium. More impo…

XRD and XAS structural study of CuAlO2under high pressure

2013

International audience; We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO2 under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO6 octahedra. The anisotropic compression is related to the chemical trends observed in the lattice pa…

Optical Properties of Self-Assembled GaxIn1-xAs/InP Quantum Wires

2002

Temperature dependent photoluminescence studies have been carried out on several samples containing self-assembled Ga x In 1-x As/InP quantum wires. A red-shift of the emission wavelength is observed when increasing the Ga content in the alloy, but the overall optical quality decreases. In the case of x = 0.15, the photoluminescence is not sensible to temperature and the emission band is conserved until room temperature is reached, which could be explained if the nanostructures are considered to be almost amorphous.

Characterization of prehispanic cosmetics found in a burial of the ancient city of Teotihuacan (Mexico)

2012

The present paper reports the chemical data obtained on samples of pigmenting materials contained in 31 miniature vessels found in a burial found in Teopancazco, a multiethnic neighborhood center located in the southeastern sector of the archaeological site of Teotihuacan (Central Mexico) and the analytical protocol established for the complete characterization of these archaeological materials. For this purpose a multi-technique approach based on the combination of several non destructive and micro-destructive instrumental techniques, namely, light microscopy (LM), scanning electron microscopy-X-ray micro-analysis (SEMe EDX), transmission electron microscopy (TEM), voltammetry of micropart…

Mangiferin nanoemulsions in treatment of inflammatory disorders and skin regeneration

2018

Abstract In this paper mangiferin nanoemulsions were developed using hyaluronic acid of different molecular weight, in absence or presence of Transcutol-P. An extensive study was carried out on the physico-chemical properties of nanoemulsions. Nanosizer and transmission electron microscopy showed oil droplets average size 296 nm with monodisperses distribution (PI ≤ 0.30). The zeta potential was highly negative (−30 mV). FTIR analysis confirms the existence of physical interactions among compounds. Rheological measurements allowed to conclude that all formulations present a pseudoplastic behavior (s ∼ 0.4) in presence of the biopolymer. Moreover, mangiferin release depends on the molecular …

A structural comparison of halloysite nanotubes of different origin by Small-Angle Neutron Scattering (SANS) and Electric Birefringence

2018

The structure of halloysite nanotubes (Hal) from different mines was investigated by Small-Angle Neutron Scattering (SANS) and Electric Birefringence (EBR) experiments. The analysis of the SANS curves allowed us to correlate the sizes and polydispersity and the specific surfaces (obtained by a Porod analysis of the SANS data) of the nanotubes with their specific geological setting. Contrast matching measurements were performed on patch Hal (from Western Australia) in order to determine their experimental scattering length density for a more precise analysis. Further characterization of the mesoscopic structure of Hal was carried out by Electric Birefringence (EBR), which allowed to study th…

Enhanced flexibility and electron-beam-controlled shape recovery in alumina-coated Au and Ag core–shell nanowires

2017

The proper choice of coating materials and methods in core–shell nanowire (NW) engineering is crucial to assuring improved characteristics or even new functionalities of the resulting composite structures. In this paper, we have reported electron-beam-induced reversible elastic-to-plastic transition in Ag/Al2O3 and Au/Al2O3 NWs prepared by the coating of Ag and Au NWs with Al2O3 by low-temperature atomic layer deposition. The observed phenomenon enabled freezing the bent core–shell NW at any arbitrary curvature below the yield strength of the materials and later restoring its initially straight profile by irradiating the NW with electrons. In addition, we demonstrated that the coating effic…