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- ItemCarboxylated nitrile butadiene rubber/hybrid filler composites(São Carlos : Universidade Federal de São Carlos, 2012) Mousa, A.; Heinrich, G.; Simon, F.; Wagenknecht, U.; Stöckelhuber, K.-W.; Dweiri, R.The surface properties of the OSW and NLS are measured with the dynamic contact-angle technique. The x-ray photoelectron spectroscopy (XPS) of the OSW reveals that the OSW possesses various reactive functional groups namely hydroxyl groups (OH). Hybrid filler from NLS and OSW were incorporated into carboxylated nitrile rubber (XNBR) to produce XNBR hybrid composites. The reaction of OH groups from the OSW with COOH of the XNBR is checked by attenuated total reflectance spectra (ATR-IR) of the composites. The degree of curing ΔM (maximum torque-minimum torque) as a function of hybrid filler as derived from moving die rheometer (MDR) is reported. The stress-strain behavior of the hybrid composites as well as the dynamic mechanical thermal analysis (DMTA) is studied. Bonding quality and dispersion of the hybrid filler with and in XNBR are examined using scanning-transmission electron microscopy (STEM in SEM).
- ItemExcited-state relaxation of hydrated thymine and thymidine measured by liquid-jet photoelectron spectroscopy: experiment and simulation(Washington, DC : ACS Publications, 2015) Buchner, Franziska; Nakayama, Akira; Yamazaki, Shohei; Ritze, Hans-Hermann; Lübcke, AndreaTime-resolved photoelectron spectroscopy is performed on thymine and thymidine in aqueous solution to study the excited-state relaxation dynamics of these molecules. We find two contributions with sub-ps lifetimes in line with recent excited-state QM/MM molecular dynamics simulations (J. Chem. Phys.2013, 139, 214304). The temporal evolution of ionization energies for the excited ππ* state along the QM/MM molecular dynamics trajectories were calculated and are compatible with experimental results, where the two contributions correspond to the relaxation paths in the ππ* state involving different conical intersections with the ground state. Theoretical calculations also show that ionization from the nπ* state is possible at the given photon energies, but we have not found any experimental indication for signal from the nπ* state. In contrast to currently accepted relaxation mechanisms, we suggest that the nπ* state is not involved in the relaxation process of thymine in aqueous solution.
- ItemRobust transverse structures in rescattered photoelectron wavepackets and their consequences(Bristol : IOP Publ., 2020) Bredtmann, T.; Patchkovskii, S.Initial-state symmetry has been under-appreciated in strong-field spectroscopies, where laser fields dominate the dynamics. We demonstrate numerically that the transverse photoelectron phase structure, arising from the initial-state symmetry, is robust in strong-field rescattering, and has pronounced effects on strong-field photoelectron spectra. Interpretation of rescattering experiments need to take these symmetry effects into account. In turn, robust transverse photoelectron phase structures may enable attosecond sub-Ångström super-resolution imaging with structured electron beams.
- ItemPhotoelectron holography in strong optical and dc electric fields(Bristol : Institute of Physics Publishing, 2014) Stodolna, A.; Huismans, Y.; Rouzée, A.; Lépine, F.; Vrakking, M.J.J.The application of velocity map imaging for the detection of photoelectrons resulting from atomic or molecular ionization allows the observation of interferometric, and in some cases holographic structures that contain detailed information on the target from which the photoelecrons are extracted. In this contribution we present three recent examples of the use of photoelectron velocity map imaging in experiments where atoms are exposed to strong optical and dc electric fields. We discuss (i) observations of the nodal structure of Stark states of hydrogen measured in a dc electric field, (ii) mid-infrared strong-field ionization of metastable Xe atoms and (iii) the reconstruction of helium electronic wavepackets in an attosecond pump-probe experiment. In each case, the interference between direct and indirect electron pathways, reminiscent of the reference and signal waves in holography, is seen to play an important role.
- ItemGeneral Time-Dependent Configuration-Interaction Singles II: The Atomic Case(Woodbury, NY : Inst., 2022-10-10) Carlström, Stefanos; Bertolino, Mattias; Dahlström, Jan Marcus; Patchkovskii, SergueiWe present a specialization of the grid-based implementation of the time-dependent configuration-interaction singles described in the preceding paper [S. Carlström et al., preceding paper, Phys. Rev. A 106, 043104 (2022)]. to the case of spherical symmetry. We describe the intricate time propagator in detail and conclude with a few example calculations. Among these, of note are high-resolution photoelectron spectra in the vicinity of the Fano resonances in photoionization of neon and spin-polarized photoelectrons from xenon, in agreement with recent experiments.
- ItemLow-energy constraints on photoelectron spectra measured from liquid water and aqueous solutions(Cambridge : RSC Publ., 2021) Malerz, Sebastian; Trinter, Florian; Hergenhahn, Uwe; Ghrist, Aaron; Ali, Hebatallah; Nicolas, Christophe; Saak, Clara-Magdalena; Richter, Clemens; Hartweg, Sebastian; Nahon, Laurent; Lee, Chin; Goy, Claudia; Neumark, Daniel M; Meijer, Gerard; Wilkinson, Iain; Winter, Bernd; Thürmer, StephanWe report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV, on the photoemission spectra of liquid water. We show that the nascent photoelectron spectrum and, hence, the inferred electron binding energy can only be accurately determined if electron energies are large enough that cross sections for quasi-elastic scattering processes, such as vibrational excitation, are negligible. Otherwise, quasi-elastic scattering leads to strong, down-to-few-meV kinetic energy scattering losses from the direct photoelectron features, which manifest in severely distorted intrinsic photoelectron peak shapes. The associated cross-over point from predominant (known) electronically inelastic to quasi-elastic scattering seems to arise at surprisingly large electron kinetic energies, of approximately 10–14 eV. Concomitantly, we present evidence for the onset of indirect, autoionization phenomena (occurring via superexcited states) within a few eV of the primary and secondary ionization thresholds. These processes are inferred to compete with the direct ionization channels and primarily produce low-energy photoelectrons at photon and electron impact excitation energies below ∼15 eV. Our results highlight that vibrational inelastic electron scattering processes and neutral photoexcitation and autoionization channels become increasingly important when photon and electron kinetic energies are decreased towards the ionization threshold. Correspondingly, we show that for neat water and aqueous solutions, great care must be taken when quantitatively analyzing photoelectron spectra measured too close to the ionization threshold. Such care is essential for the accurate determination of solvent and solute ionization energies as well as photoelectron branching ratios and peak magnitudes.
- ItemPhotoemission of Bi2Se3 with circularly polarized light: Probe of spin polarization or means for spin manipulation?(College Park : American Institute of Physics Inc., 2014) Sánchez-Barriga, J.; Varykhalov, A.; Braun, J.; Xu, S.-Y.; Alidoust, N.; Kornilov, O.; Minár, J.; Hummer, K.; Springholz, G.; Bauer, G.; Schumann, R.; Yashina, L.V.; Ebert, H.; Hasan, M.Z.; Rader, O.Topological insulators are characterized by Dirac-cone surface states with electron spins locked perpendicular to their linear momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy.We solve this puzzle and show that vacuum ultraviolet photons (50-70 eV) with linear or circular polarization indeed probe the initial-state spin texture of Bi2Se3 while circularly polarized 6-eV low-energy photons flip the electron spins out of plane and reverse their spin polarization, with its sign determined by the light helicity. Our photoemission calculations, taking into account the interplay between the varying probing depth, dipole-selection rules, and spin-dependent scattering effects involving initial and final states, explain these findings and reveal proper conditions for light-induced spin manipulation. Our results pave the way for future applications of topological insulators in optospintronic devices.
- ItemTowards time resolved core level photoelectron spectroscopy with femtosecond x-ray free-electron lasers(College Park, MD : Institute of Physics Publishing, 2008) Pietzsch, A.; Föhlisch, A.; Beye, M.; Deppe, M.; Hennies, F.; Nagasono, M.; Suljotil, E.; Wurth, W.; Gahl, C.; Dörich, K.; Melnikov, A.We have performed core level photoelectron spectroscopy on a W(110) single crystal with femtosecond XUV pulses from the free-electron laser at Hamburg (FLASH). We demonstrate experimentally and through theoretical modelling that for a suitable range of photon fluences per pulse, time-resolved photoemission experiments on solid surfaces are possible. Using FLASH pulses in combination with a synchronized optical laser, we have performed femtosecond time-resolved core-level photoelectron spectroscopy and observed sideband formation on the W 4f lines indicating a cross correlation between femtosecond optical and XUV pulses. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemPinning of the Fermi Level in CuFeO2 by Polaron Formation Limiting the Photovoltage for Photochemical Water Splitting(Weinheim : Wiley-VCH Verlag, 2020) Hermans Y.; Klein A.; Sarker H.P.; Huda M.N.; Junge H.; Toupance T.; Jaegermann W.CuFeO2 is recognized as a potential photocathode for photo(electro)chemical water splitting. However, photocurrents with CuFeO2-based systems are rather low so far. In order to optimize charge carrier separation and water reduction kinetics, defined CuFeO2/Pt, CuFeO2/Ag, and CuFeO2/NiOx(OH)y heterostructures are made in this work through a photodeposition procedure based on a 2H CuFeO2 hexagonal nanoplatelet shaped powder. However, water splitting performance tests in a closed batch photoreactor show that these heterostructured powders exhibit limited water reduction efficiencies. To test whether Fermi level pinning intrinsically limits the water reduction capacity of CuFeO2, the Fermi level tunability in CuFeO2 is evaluated by creating CuFeO2/ITO and CuFeO2/H2O interfaces and analyzing the electronic and chemical properties of the interfaces through photoelectron spectroscopy. The results indicate that Fermi level pinning at the Fe3+/Fe2+ electron polaron formation level may intrinsically prohibit CuFeO2 from acquiring enough photovoltage to reach the water reduction potential. This result is complemented with density functional theory calculations as well. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim