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XPS-UPS Systems

XPS/UPS systems are a standard tool for the characterization of the chemical composition and the electronic structure of the surfaces of solids. Often a preparation chamber is integrated, so that samples inserted through the Load Lock chamber can be cleaned before analysis. Integration of sputter depth profiling, Auger electron spectroscopy, (R)EELS or Ion scattering spectroscopy is easily possible in the measurement position to get a more holistic insight into the properties of the samples.By using small spot sources, a 2D-detector and stage mapping, chemical mapping of the surface is possible, as well, to characterize the inhomogeneous element distribution on technical sample surfaces.



  1. (2017) Catalytic consequences of Ga promotion on Cu for CO2 hydrogenation to methanol

    The promotion of Ga on SiO2 supported Cu in the hydrogenation of CO2 to methanol at 800 kPa and 200–280 °C was investigated. Cu/SiO2 and CuGa/SiO2 catalysts were prepared by a water-in-oil microemulsion technique resulting in Cu clusters of 4–6.5 nm. It was found that Ga addition increased the methanol formation rate by an order of magnitude without significantly changing that for reverse water gas shift (RWGS). This trend is also evidenced by the decrease in the apparent activation barrier for methanol formation from 78 (for Cu/SiO2) to 26–39 kJ mol−1 when Ga was added, but not for RWGS (107–132 kJ mol−1). Kinetic and in situ DRIFTS analyses revealed that formate intermediates are adsorbed on both Cu and Ga2O3 and that methoxy hydrogenation could be the rate determining step of methanol synthesis. In the case of RWGS, a zero order of CO formation with respect to H2 concentration was consistent with a redox mechanism and with the reaction occurring predominantly on Cu sites. The results suggest that Ga promotes Cu increasing methanol selectivity, likely by creating new active sites for methanol formation without modifying its oxidation state, which under reaction conditions remains mostly metallic.

    J. C. Medina, M. Figueroa, R. Manrique, J. R. Pereira, P. D. Srinivasan, J. J. Bravo-Suárez, V. G. Baldovino Medrano, R. Jiméneza and A. Karelovic
    Catal. Sci. Technol., 2017,7, 3375-3387
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  2. (2019) Insights into the role of Zn and Ga in the hydrogenation of CO2 to methanol over Pd

    The hydrogenation of CO2 to methanol is a viable alternative for reducing greenhouse gases net emissions as well as a route for hydrogen storage and transportation. In this context, the synthesis of active and selective catalysts is a relevant objective. In this work, we study the promotion of Pd with Ga and Zn in the hydrogenation of CO2 to methanol at 800 kPa and 220–280 °C. Mono and intermetallic catalysts (Pd/SiO2, PdGa/SiO2 and Pd-Zn/SiO2) were synthesized by incipient wetness impregnation with the aid of triethanolamine as an organic additive, obtaining similar average metal particle sizes (between 9 and 12 nm). Kinetic analysis reveals that the addition of Ga and Zn increases the turnover frequency for methanol formation by an order of magnitude without significant changes in the reaction rate of the reverse water-gas shift (r-WGS) which is a parallel undesired reaction. The selectivity to methanol (at 220 °C) thus increases from 3% for Pd/SiO2 to 12% for Pd-Ga/SiO2 and 30% for Pd-Zn/SiO2. XPS studies, Infrared analysis of CO adsorption, and XRD analyses show the presence of intermetallic phases Pd2Ga and PdZn on the surface. The results suggest that Ga and Zn promote Pd, increasing its activity towards the synthesis of methanol, by creating more active sites for this reaction. These sites are likely formed by intermetallic compounds such as Pd2Ga and PdZn.

    R. Manrique, R. Jiménez, J. Rodríguez-Pereira, V. G. Baldovino-Medrano, and A. Karelovic
    International Journal of Hydrogen Energy, Volume 44, Issue 31, 21 June 2019, Pages 16526-16536
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  3. (2021) <p>Epitaxial thin-film Pd<sub>1−x</sub>Fe<sub>x</sub> alloy: a tunable ferromagnet for superconducting spintronics</p>

    Thin epitaxial films of the palladium-rich Pd1−xFex alloy were synthesized and extensively studied as a tunable ferromagnetic material for superconducting spintronics. The (001)-oriented MgO single-crystal substrate and the composition range of x = 0.01–0.07 were chosen to support the epitaxial growth and provide the films with magnetic properties spanning from very soft ferromagnet for memory applications to intermediately soft and moderately hard for the programmable logic and circuit biasing, respectively. Dependences of the saturation magnetization, Curie temperature and three magnetic anisotropy constants on the iron content x were obtained for the first time from the analyses of the magnetometry and ferromagnetic resonance data. The experimental results were discussed based on existing theories of dilute ferromagnetic alloys. Simulation of the hysteresis loops within the Stoner-Wohlfarth model indicates the predominant coherent magnetic moment rotation at cryogenic temperatures. The obtained results were compiled in a database of magnetic properties of a palladium-iron alloy in a single-crystal thin-film form considered as a material for superconducting spintronics.

    A. Esmaeili, I. V. Yanilkin, A. I. Gumarov, I. R. Vakhitov, B. F. Gabbasov, R. V. Yusupov,
    D. A. Tatarsky, and L. R. Tagirov
    Science China Materials volume 64, pages 1246–1255 (2021)
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  4. (2019) <p>Epitaxial growth of Pd<sub>1−x </sub>Fe<sub>x</sub> films on MgO single-crystal substrate</p>

    In the paper we report on growth conditions, morphology, crystallographic structure and magnetic anisotropy of 20 nm thick, palladium-rich Pd1−xFex (0.01 < x < 0.1) alloy films grown on (001)-oriented MgO single-crystal substrate. Molecular beam deposition at ultra-high vacuum conditions has been utilized along with the three-step procedure to achieve the epitaxy conditions for the synthesized films. The scanning electron microscopy and atomic force microscopy have shown flat and smooth morphology of the films studied in a wide range of lateral scales. In situ low energy electron diffraction and ex situ X-ray diffraction measurements confirmed that our Pd1−xFex alloy films are epitaxial. Ferromagnetic resonance investigations have shown the in-plane four-fold magnetocrystalline anisotropy characteristic for single-crystalline films with the cubic structure. The whole set of our measurements testifies the epitaxial cube-on-cube growth and excellent magnetic homogeneity of Pd1−xFex films on MgO substrate obtained within the three-step deposition process.

    A. Esmaeilia, I.V. Yanilkina, A.I. Gumarova, I.R. Vakhitova, B.F. Gabbasova, A.G. Kiiamova,
    A.M. Rogova, Yu.N. Osina, A.E. Denisova, R.V. Yusupova, and L.R. Tagirova
    Thin Solid Films 669 (2019) 338–344
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  5. (2021) <p>Synthesis, Characterization, and Magnetoresistive Properties of the Epitaxial Pd<sub>0.96</sub>Fe<sub>0.04 </sub>/VN/Pd <sub>0.92 </sub>Fe <sub>0.08</sub> Superconducting Spin-Valve Heterostructure</p>

    A thin-film superconductor(S)/ferromagnet(F) F1/S/F2-type Pd0.96Fe0.04 (20 nm)/VN(30 nm)/Pd0.92Fe0.08 (12 nm) heteroepitaxial structure was synthesized on (001)-oriented single-crystal MgO substrate utilizing a combination of the reactive magnetron sputtering and the molecular-beam epitaxy techniques in ultrahigh vacuum conditions. The reference VN film, Pd0.96Fe0.04 /VN, and VN/Pd0.92 Fe0.08 bilayers were grown in one run with the target sample. In-situ low-energy electron diffraction and ex-situ X-ray diffraction investigations approved that all the Pd1−xFex and VN layers in the series grew epitaxial in a cube-on-cube mode. Electric resistance measurements demonstrated sharp transitions to the superconducting state with the critical temperature reducing gradually from 7.7 to 5.4 K in the sequence of the VN film, Pd0.96 Fe0.04 /VN, VN/Pd0.92Fe0.08 , and Pd0.96Fe0.04 /VN/Pd0.92Fe0.08 heterostructures due to the superconductor/ferromagnet proximity effect. Transition width increased in the same sequence from 21 to 40 mK. Magnetoresistance studies of the trilayer Pd0.96Fe0.04 /VN/Pd0.92 Fe0.08 sample revealed a superconducting spin-valve effect upon switching between the parallel and antiparallel magnetic configurations, and anomalies associated with the magnetic moment reversals of the ferromagnetic Pd0.92Fe0.08 and Pd0.96Fe0.04 alloy layers. The moderate critical temperature suppression and manifestations of superconducting spin-valve properties make this kind of material promising for superconducting spintronics applications.

    I. Yanilkin, W. Mohammed, A. Gumarov, A. Kiiamov, R. Yusupov, and L. Tagirov
    Nanomaterials 2021, 11, 64
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