Papers by Keyword: X-Ray Absorption

Abstract: Transitioning from combustion engine-driven transportation to e-mobility demands a paradigm shift – from a system geared to maximize energy efficiency (i.e. fuel consumption) to a system that may be constrained by the availability of high technology (critical) metals required for electrical energy storage systems and drives. In the wake of these developments efforts in securing new resources of these metals from recycling of end-of-life products are increasing steadily.

Abstract: Recently there has been a very high demand for small scale magnetic storage devices. The industry sector has consistently demanded sub micron or even nanometer scale magnets. Magnetic thin films often contain several layers of coating. For the purpose of this study, we prepared thin film magnets by spin coating a precursor containing iron into a glass substrate. The thickness of the films was controlled by the spin rate. Precursor films on the substrate were then annealed to 600⁰ C for 3 hours in air. The micro structure of iron in the films was investigated using the pre-edge feature that appears in the X-ray Absorption Near Edge Structure (XANES) for samples containing different iron layers. The main absorption edge peak position and pre-edge energy position were identical in all of the samples. This indicates that there was no change in the charge state of the iron regardless of the number of layers. However the intensity of the pre-edge feature decreases as number of layers increases which shows a decrease of Fe-O compounds as the number of layers increases.

Abstract: High-resolution synchrotron radiation X-ray absorption of Si K-edge have been employed to investigate 6H-, 4H- and 3C-SiC. Detailed analyses of the extended x-ray absorption fine structure are taken by using the IFEFFIT program, and significant results on the atomic bonding are obtained from these comparative studies. The x-ray absorption near-edge structures of the Si K-edge are investigated, and the electronic structure of 3C-, 4H- and 6H-SiC are studied. In order to investigate the angular dependence, the x-ray absorption near-edge spectra were operated at 55o and 90o of the angle between the surface and the X-ray direction.

Abstract: FTIR, Visible and UV Raman scattering, as well as synchrotron radiation X-ray absorption, in combination, have been employed to investigate a series of CVD grown 3C-SiC/Si (100). Significant results on the optical and atomic bonding properties are obtained from these comparative studies.

Abstract: Synchrotron radiation X-ray absorption and UV 325 nm excitation Raman scattering- photoluminescence (PL) have been employed to investigate a series of 4H-SiC wafers, including bulk, epitaxial single or multiple layer structures by chemical vapor deposition. Significant results on the atomic bonding and PL-Raman properties are obtained from these comparative studies.

Abstract: Synchrotron radiation extended X-ray absorption fine structure and Raman scattering were used to characterize a series of 3C-SiC films grown on Si (100) by chemical vapor deposition. EXAFS can probe the physical and chemical structure of matters at an atomic scale and Raman parameters such as intensity, width, peak frequency and polarization provide fruitful information on the crystal quality and properties of these film materials.

Abstract: X-Rays Absorption Fine Structure Spectroscopy (XAFS) is an analytical technique that can be used as a probe to characterize almost all elements, even if they appear in diluted or non-crystalline systems. This is due to the fact that the absorption probability of X-rays has a unique feature for each element, and is modulated by the chemical and physical state of that element, as well as by its neighborhood. This paper presents a brief description of the X-rays absorption phenomenon and the analytical technique involving this phenomenon, as well as the application of XAFS in biosorption studies. For more details on XAFS theory, refer to [1].

Abstract: Solid particles of ferric oxyhydroxides or iron oxide were recrystallized from ferrous and ferric ions dissolved in aqueous solution. There are different structures of α-FeOOH, β-FeOOH and γ-FeOOH in the ferric oxyhydroxides, of which the formation is influenced by reaction conditions such as oxidation rate of ferrous ions. In this work, a few factors affecting the formation of the ferric oxyhydroxides and iron oxides, which was converted from hydrosulfate green rust, has been studied using different methods. The hydrosulfate green rust (GR2) was synthesized from solutions of ferric sulfate (Fe2(SO4)3), ferrous sulfate (FeSO4), and sodium hydroxide (NaOH), and they were oxidized by gas containing oxygen. X-ray diffraction measurements and X-ray absorption spectroscopy were used for analyzing the structure and chemical state of solid particles extracted from the suspension during the oxidation. The morphology of the particles was observed by transmission electron microscopy. The results showed that γ-FeOOH or Fe3O4 particles were formed together with α-FeOOH particles during conversion from the green rust, depending on oxidation temperature, oxygen flow rate and addition of manganese. This indicates that the species of ferric oxyhydroxides or iron oxides formed in aqueous solution is sensitively influenced by reaction conditions.

Abstract: Hydrogen separation is one of the key techniques for the forthcoming hydrogen economy. This paper describes a possible electrochemical method and materials for hydrogen separation: mixed proton-electron-conducting membrane that can permeate hydrogen selectively from hydrogen-containing gases, such as reformed gases of hydrocarbons. Proton-conducting perovskite-type solid electrolytes are first introduced as the base material of the mixed conductor. Some transition metal-doped perovskites are shown to have a mixed conductivity of protonic and electronic charge carriers, revealed by electrochemical and X-ray-spectroscopic measurements.

Abstract: The elemental magnetic moments of Co and Cr in CoCrPt films were investigated using xray magnetic circular dichroism (XMCD). The spin and orbital moments of Co was calculated using the sum rules; it was found that the magnetic moment of Co in CoCrPt films was dominated by spin moment contribution. The total magnetic moment of Co was found to be lower than that of bulk Co. Further, the Cr moment was aligned anti-ferromagnetically with respect to Co, resulting in a decrease of saturation magnetization (Ms) in CoCrPt films.