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- ItemEnhanced thermal stability of yttrium oxide-based RRAM devices with inhomogeneous Schottky-barrier(Melville, NY : American Inst. of Physics, 2020) Piros, Eszter; Petzold, Stefan; Zintler, Alexander; Kaiser, Nico; Vogel, Tobias; Eilhardt, Robert; Wenger, Christian; Molina-Luna, Leopoldo; Alff, LambertThis work addresses the thermal stability of bipolar resistive switching in yttrium oxide-based resistive random access memory revealed through the temperature dependence of the DC switching behavior. The operation voltages, current levels, and charge transport mechanisms are investigated at 25 °C, 85 °C, and 125 °C, and show overall good temperature immunity. The set and reset voltages, as well as the device resistance in both the high and low resistive states, are found to scale inversely with increasing temperatures. The Schottky-barrier height was observed to increase from approximately 1.02 eV at 25 °C to approximately 1.35 eV at 125 °C, an uncommon behavior explained by interface phenomena. © 2020 Author(s).
- ItemCharge carrier density, mobility, and Seebeck coefficient of melt-grown bulk ZnGa2O4 single crystals(New York, NY : American Inst. of Physics, 2020) Boy, Johannes; Handwerg, Martin; Mitdank, Rüdiger; Galazka, Zbigniew; Fischer, Saskia F.The temperature dependence of the charge carrier density, mobility, and Seebeck coefficient of melt-grown, bulk ZnGa2O4 single crystals was measured between 10 K and 310 K. The electrical conductivity at room temperature is about σ = 286 S/cm due to a high electron concentration of n = 3.26 × 1019 cm−3 caused by unintentional doping. The mobility at room temperature is μ = 55 cm2/V s, whereas the scattering on ionized impurities limits the mobility to μ = 62 cm2/Vs for temperatures lower than 180 K. The Seebeck coefficient relative to aluminum at room temperature is SZnGa2O4−Al = (−125 ± 2) μV/K and shows a temperature dependence as expected for degenerate semiconductors. At low temperatures, around 60 K, we observed the maximum Seebeck coefficient due to the phonon drag effect. © 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
- ItemTemperature dependence of the complex permittivity in microwave range of some industrial polymers(New York, NY : American Inst. of Physics, 2022) Porteanu, Horia-Eugen; Kaempf, Rudolf; Flisgen, Thomas; Heinrich, WolfgangThe microwave properties of a number of polymers common in industry are investigated. A cylindrical resonator in the TM012 mode is used. The cavity perturbation method and detailed COMSOL simulations are applied for extracting the complex permittivity as a function of temperature. The results are useful for the design of plastic processing tools by heating with electromagnetic fields. The intrinsic parameters of absorption are derived based on two exponential decays: polarization and Arrhenius dependence of the decay times on temperature.
- ItemFemtosecond spectroscopy in a nearly optimally doped Fe-based superconductors FeSe0.5Te0.5 and Ba(Fe 1-xCox)2As2/Fe thin film(Bristol : Institute of Physics Publishing, 2014) Bonavolontà, C.; Parlato, L.; De, Lisio, C.; Valentino, M.; Pepe, G.P.; Kazumasa, I.; Kurth, F.; Bellingeri, E.; Pallecchi, I.; Putti, M.; Ferdeghini, C.; Ummarino, G.A.; Laviano, F.Femtosecond spectroscopy has been used to investigate the quasi-particle relaxation times in nearly optimally doped Fe-based superconductors FeSe 0.5Te0.5 and optimally doped Ba-122 thin films growth on a Fe buffer layer. Experimental results concerning the temperature dependence of the relaxation time of such pnictides both in the superconducting state are now presented and discussed. Modelling the T-dependence of relaxation times an estimation of both electron-phonon constant and superconducting energy gap in the excitation spectrum of both Fe(Se,Te) and Ba-122 compounds is obtained.
- ItemMechanical properties and twin boundary drag in Fe-Pd ferromagnetic shape memory foils-experiments and ab initio modeling(Bristol : IOP, 2011) Claussen, I.; Mayr, S.G.We report on vibrating reed measurements combined with density functional theory-based calculations to assess the elastic and damping properties of Fe-Pd ferromagnetic shape memory alloy splats. While the austenite-martensite phase transformation is generally accompanied by lattice softening, a severe modulus defect and elevated damping behavior are characteristic of the martensitic state. We interpret the latter in terms of twin boundary motion between pinning defects via partial 'twinning' dislocations. Energy dissipation is governed by twin boundary drag, primarily due to lattice imperfections, as concluded from the temperature dependence of damping and related activation enthalpies.
- ItemMomentum-resolved superconducting gap in the bulk of Ba1-xK xFe2As2 from combined ARPES and μSR measurements(Milton Park : Taylor & Francis, 2009) Evtushinsky, D.V.; Inosov, D.S.; Zabolotnyy, V.B.; Viazovska, M.S.; Khasanov, R.; Amato, A.; Klauss, H.-H.; Luetkens, H.; Niedermayer, Ch.; Sun, G.L.; Hinkov, V.; Lin, C.T.; Varykhalov, A.; Koitzsch, A.; Knupfer, M.; Büchner, B.; Kordyuk, A.A.; Borisenko, S.V.Here we present a calculation of the temperature-dependent London penetration depth, λ(T), in Ba1-xKxFe 2As2 (BKFA) on the basis of the electronic band structure (Zabolotnyy et al 2009 Nature 457 569, Zabolotnyy et al 2009 Physica C 469 448) and momentum-dependent superconducting gap (Evtushinsky et al 2009 Phys. Rev. B 79 054517) extracted from angleresolved photoemission spectroscopy (ARPES) data. The results are compared to the direct measurements of λ(T) by muon spin rotation (μSR) (Khasanov et al 2009 Phys. Rev. Lett. 102 187005). The value of λ(T = 0), calculated with no adjustable parameters, equals 270 nm, while the directly measured one is 320 nm; the temperature dependence λ(T) is also easily reproduced. Such agreement between the two completely different approaches allows us to conclude that ARPES studies of BKFA are bulk-representative. Our review of the available experimental studies of the superconducting gap in the new ironbased superconductors in general allows us to state that most of them bear two nearly isotropic gaps with coupling constants 2ΔkBTc = 2.5±1.5 and 7±2.
- ItemTropospheric Aqueous-Phase Oxidation of Isoprene-Derived Dihydroxycarbonyl Compounds(Washington, DC : Soc., 2017) Otto, Tobias; Stieger, Bastian; Mettke, Peter; Herrmann, HartmutThe dihydroxycarbonyls 3,4-dihydroxy-2-butanone (DHBO) and 2,3-dihydroxy-2-methylpropanal (DHMP) formed from isoprene oxidation products in the atmospheric gas phase under low-NO conditions can be expected to form aqSOA in the tropospheric aqueous phase because of their solubility. In the present study, DHBO and DHMP were investigated concerning their radical-driven aqueous-phase oxidation reaction kinetics. For DHBO and DHMP the following rate constants at 298 K are reported: k(OH + DHBO) = (1.0 ± 0.1) × 109 L mol-1 s-1, k(NO3 + DHBO) = (2.6 ± 1.6) × 106 L mol-1 s-1, k(SO4-+ DHBO) = (2.3 ± 0.2) × 107 L mol-1 s-1, k(OH + DHMP) = (1.2 ± 0.1) × 109 L mol-1 s-1, k (NO3 + DHMP) = (7.9 ± 0.7) × 106 L mol-1 s-1, k(SO4- + DHMP) = (3.3 ± 0.2) × 107 L mol-1 s-1, together with their respective temperature dependences. The product studies of both DHBO and DHMP revealed hydroxydicarbonyls, short chain carbonyls, and carboxylic acids, such as hydroxyacetone, methylglyoxal, and lactic and pyruvic acid as oxidation products with single yields up to 25%. The achieved carbon balance was 75% for DHBO and 67% for DHMP. An aqueous-phase oxidation scheme for both DHBO and DHMP was developed on the basis of the experimental findings to show their potential to contribute to the aqSOA formation. It can be expected that the main contribution to aqSOA occurs via acid formation while other short-chain oxidation products are expected to back-partition into the gas phase to undergo further oxidation there.