154 research outputs found
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Characterization of L21 order in Co2FeSi thin films on GaAs
Co2FeSi/GaAs(110) and Co2FeSi/GaAs(-1-1-1)B hybrid structures were grown by molecular-beam epitaxy (MBE) and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The films contain inhomogeneous distributions of ordered L21 and B2 phases. The average stoichiometry could be determined by XRD for calibration of the MBE sources. Diffusion processes lead to inhomogeneities, influencing long-range order. An average L21 ordering of up to 65% was measured by grazing-incidence XRD. Lateral inhomogeneities of the spatial distribution of long-range order in Co2FeSi were imaged using dark-field TEM with superlattice reflections and shown to correspond to variations of the Co/Fe ratio
Surface acoustic wave propagation in graphene film
Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals
Adsorption and diffusion of selenite on Boda Claystone Formation
This study provides adsorption and diffusion data of selenite on Boda Claystone Formation (BCF) which is a potential host rock of a deep geological disposal of high-level radioactive waste. The experiments were performed on two diverse core samples: one albitic claystone sample characteristic for the entire BCF and one pyrite containing sample sparsely occurring in BCF. The experiments were carried out under atmospheric conditions. Batch experiments were carried out to study the kinetics of adsorption at a high initial concentration (1.2 × 10−3 M), the adsorption isotherms and reversibility were investigated in the 10−10–10−3 M concentration range. Adsorption onto petrographic thin sections was done to study the elemental distribution on the microscale and the oxidation state of selenium. The maximum of the distribution coefficient was found as Kd ≈ 200 L/kg and a decrease was experienced around 10−6–10−7 M equilibrium concentration, which showed similarities to other argillaceous rocks. Isotopic exchange experiments revealed reversibility of selenite adsorption. Diffusion was studied with through-diffusion and in-diffusion experiments. Using X-ray fluorescence, despite a low initial concentration of 2.3 × 10−5 M in the in-diffusion experiment, a meaningful diffusion profile of selenium could be obtained, from which the selenite apparent diffusion coefficient Dappselenite = (1.5–4.3) × 10−14 m2/s and the selenite rock capacity factor αselenite = 1.4–2.2 were determined. As selenium species are redox sensitive the oxidation state of adsorbed species was studied with X-ray absorption near edge structure spectroscopy on Se–K edge. Adsorbed selenium remained in +IV oxidation state, however reduction was experienced on the pyritic sample
PO-410 Cytotoxicity and genotoxicity of new gadolinium, iron oxide, cobalt ferrite and graphene oxide nanoparticles on some tumour cell lines in vitro
Nanoparticles (NPs) are increasingly used in cancer
therapy as delivery agents and in the diagnosis of malignant diseases
as contrast agents for magnetic resonance imaging (MRI).
The aim of this work was in vitro assessments of Gd-NPs, Fe-
NPs, CoFe-NPs and Graphene Oxide-NPs cytotoxicity and genotoxicity
on some tumour and normal human cell lines.Abstracts of the 25th Biennial Congress of the European Association for Cancer Research, Amsterdam, The Netherlands, 30 June – 3 July 201
Water oxidation catalysis – role of redox and structural dynamics in biological photosynthesis and inorganic manganese oxides
Water oxidation is pivotal in biological photosynthesis, where it is catalyzed
by a protein-bound metal complex with a Mn4Ca-oxide core; related synthetic
catalysts may become key components in non-fossil fuel technologies. Going
beyond characterization of the catalyst resting state, we compare redox and
structural dynamics of three representative birnessite-type Mn(Ca) oxides
(catalytically active versus inactive; with/without calcium) and the
biological catalyst. In the synthetic oxides, Mn oxidation was induced by
increasingly positive electrode potentials and monitored by electrochemical
freeze-quench and novel time-resolved in situ experiments involving detection
of X-ray absorption and UV-vis transients, complemented by electrochemical
impedance spectroscopy. A minority fraction of Mn(III) ions present at
catalytic potentials is found to be functionally crucial; calcium ions are
inessential but tune redox properties. Redox-state changes of the water-
oxidizing Mn oxide are similarly fast as observed in the biological catalyst
(<10 ms), but 10–100 times slower in the catalytically inactive oxide.
Surprisingly similar redox dynamics of biological catalyst and water-oxidizing
Mn(Ca) oxides suggest that in both catalysts, rather than direct oxidation of
bound water species, oxidation equivalents are accumulated before onset of the
multi-electron O–O bond formation chemistry in Mn(III)–Mn(IV) oxidation steps
coupled to changes in the oxo-bridging between metal ions. Aside from the
ability of the bulk oxide to undergo Mn oxidation-state changes, we identify
two further, likely interrelated prerequisites for catalytic activity of the
synthetic oxides: (i) the presence of Mn(III) ions at catalytic potentials
preventing formation of an inert all-Mn(IV) oxide and (ii) fast rates of
redox-state changes approaching the millisecond time domain
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