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作者： J.-S. Lee D. A. Arena T. S. Santos C. S. Nelson S. I. Hyun J. H. Shim C.-C. Kao Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park California 94025 USA National Synchrotron Light Source Brookhaven National Laboratory Upton New York 11973 USA Western Digital Corporation San Jose California 95138 USA Center for Nanoscale Materials Argonne National Laboratory Argonne IL 60439 USA Department of Chemistry Pohang University of Science and Technology Pohang 790-784 S. Korea

We investigated thin La0.7Sr0.3MnO3-SrTiO3 heterostructures, where the band alignment is engineered by a variation of La/Sr stoichiometry only at the interface. In thin films, the engineered interface leads to an enhancement of the reversed spin configuration that mimics bulk behavior. Microscopically, this enhancement is closely connected with an increased magnetic anisotropy as well as intercoupling between an eg orbital reconstruction and a corresponding anisotropic lattice fluctuation. Furthermore, a reentrant-type behavior, triggered by this intercoupling, is observed in the remanent spin state. This microscopic perspective leads to insights on developing new strategies for maintaining bulk-like properties even in very thin La0.7Sr0.3MnO3 heterostructures.

关键词： OXIDES INTERFACES (Physical sciences) ANISOTROPY LANTHANUM compounds TITANATES CRYSTAL lattices STOICHIOMETRY HETEROSTRUCTURES

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Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

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Physical Review Letters 2012年第8期108卷 087601-087601页

作者： Dan Daranciang Matthew J. Highland Haidan Wen Steve M. Young Nathaniel C. Brandt Harold Y. Hwang Michael Vattilana Matthieu Nicoul Florian Quirin John Goodfellow Tingting Qi Ilya Grinberg David M. Fritz Marco Cammarata Diling Zhu Henrik T. Lemke Donald A. Walko Eric M. Dufresne Yuelin Li Jörgen Larsson David A. Reis Klaus Sokolowski-Tinten Keith A. Nelson Andrew M. Rappe Paul H. Fuoss G. Brian Stephenson Aaron M. Lindenberg Department of Chemistry Stanford University Stanford California 94305 USA PULSE Institute for Ultrafast Energy Science SLAC National Accelerator Laboratory Menlo Park California 94025 USA Stanford Institute for Materials and Energy Science SLAC National Accelerator Laboratory Menlo Park California 94025 USA Materials Science Division Argonne National Laboratory Argonne Illinois 60439 USA Advanced Photon Source Argonne National Laboratory Argonne Illinois 60439 USA The Makineni Theoretical Laboratories Department of Chemistry University of Pennsylvania Philadelphia Pennsylvania 19104-6323 USA Department of Chemistry Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE) University of Duisburg-Essen 47048 Duisburg Germany Department of Materials Science and Engineering Stanford University Stanford California 94305 USA Linac Coherent Light Source SLAC National Accelerator Laboratory Menlo Park California 94025 USA Niels Bohr Institute University of Copenhagen 2100 Copenhagen Denmark Department of Physics Lund University S-22100 Lund Sweden Department of Applied Physics Stanford University Stanford California 94305 USA

We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.

关键词： PHOTOVOLTAIC effect FERROELECTRICITY NANOSTRUCTURED materials LAYER structure (Solids) PROTOTYPES X-ray scattering POLARIZATION (Electricity)

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Structural and morphological characterization of Mo coatings for high gradient accelerating structures

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Journal of Physics: Conference Series 2013年第1期430卷

作者： Y Xu B Spataro S Sarti V A Dolgashev S Tantawi A D Yeremian Y Higashi M G Grimaldi L Romano F Ruffino R Parodi C Caliendo A Notargiacomo G Cibin A Marcelli INFN-Laboratori Nazionali di Frascati Frascati 00044 Italy Department of Chemical Physics Anhui Key Laboratory of Biomass Clean Energy University of Science & Technology of China Hefei 230026 China University of Rome Sapienza Dipartimento di Fisica 00185 Rome Italy SLAC National Accelerator Laboratory Menlo Park CA 94025 USA KEK 1-1 Oho Tsukuba Ibaraki 305 Japan University of Catania Dipartimento di Fisica e Astronomia & MATIS-IMM-CNR 95123 Catania Italy INFN-Genova 16146 Genova Italy ISC-CNR Area della Ricerca di Roma 1 00040 Monterotondo Rome Italy Istituto di Fotonica e Nanotecnologie CNR Rome 00156 Italy Diamond Light Source Chilton Didcot Oxon OX110DE UK NSRL University of Science and Technology of China Hefei 230026 China

A series of Mo coatings grown on Al2O3 and Cu were prepared via sputtering method. XAS experiments were performed at the Mo K edge to characterize the coating structure and the chemical status of Mo atoms. From the XANES analysis we recognized that all Mo coatings on Al2O3 have a slightly disordered structure with a negligible Mo oxide contribution. Moreover, the chemical state is that of the Mo metal with a negligible oxygen contribution. Compared with Cu based materials, molybdenum is an attractive material for accelerator components and a reliable option for RF linear accelerating structures to achieve high accelerating gradients and low breakdown rates, two fundamental parameters for the next generation of linear accelerators.

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Suppression of mixed-phase areas in highly elongated BiFeO3 thin films on NdAlO3 substrates

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Physical Review B 2012年第5期86卷 054417-054417页

作者： Chang-Su Woo Jin Hong Lee Kanghyun Chu Byung-Kweon Jang Yong-Bae Kim Tae Yeong Koo Ping Yang Yajun Qi Zuhuang Chen Lang Chen Hong Chul Choi Ji Hoon Shim Chan-Ho Yang Department of Physics KAIST Daejeon 305-701 Korea Gumi Electronics & Information Technology Research Institute Gumi Gyungbuk 730-853 Korea Pohang Accelerator Laboratory Pohang Gyungbuk 705-784 Korea Singapore Synchrotron Light Source National University of Singapore Singapore 117603 Singapore School of Materials Science and Engineering 50 Nanyang Avenue Nanyang Technological University Singapore 639798 Singapore Department of Chemistry POSTECH Pohang Gyungbuk 705-784 Korea Institute for the NanoCentury KAIST Daejeon 305-701 Korea

Mixed-phase areas are produced in highly elongated BiFeO3 (BFO) thin films as a consequence of strain relaxation. A (001) neodymium aluminate (NdAlO3; NAO) substrate (a∼3.747 Å) prominently suppresses the strain relaxation effect and prevents the formation of mixed-phase regions. This creates a pathway to the thick, quasipure, highly elongated phases required for magnetoelectric applications. We characterize the crystal structure, the interface between film and substrate, the surface morphology, and the ferroelectric domain structure of BFO films on NAO substrates and compare them with those of films on typical lanthanum aluminate substrates. The underlying mechanisms are discussed based on the intriguing nature of phase competition in bismuth ferrite phases using first principles density functional calculations for the misfit strain-dependent total energy.

关键词： IRON oxides THIN films SUBSTRATES (Materials science) STRAINS & stresses (Mechanics) THICKNESS measurement MAGNETOELECTRIC effect CRYSTAL structure

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Controlling spin ordering in frustrated magnets via thin film heteroepitaxy

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Physical Review B 2012年第21期85卷 214424-214424页

作者： Jodi M. Iwata-Harms Franklin J. Wong Urusa S. Alaan B. J. Kirby Julie A. Borchers Michael F. Toney Brittany B. Nelson-Cheeseman Marco Liberati Elke Arenholz Yuri Suzuki Department of Materials Science and Engineering University of California Berkeley California 94720 USA Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park California 94025 USA Advanced Light Source Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Applied Physics and Geballe Laboratory for Advanced Materials Stanford University Stanford California 94305 USA

Competing exchange interactions can give rise to varying degrees of frustration that manifest itself in noncollinear magnetic moment ordering or canonical geometric frustration in magnets with large ground-state degeneracies. Relieving this frustration has the potential to stabilize ground states inaccessible in the bulk. We demonstrate that heteroepitaxial lattice distortions can modify the strength of exchange interactions in thin films of the frustrated ferrimagnet, CuCr2O4. The reduction of magnetic frustration in CuCr2O4 through lattice distortions results in greater collinear spin ordering in CuCr2O4 thin films and an enhanced magnetization. We identify heteroepitaxial lattice distortions as a method to tune spin functionality and potentially lift ground-state degeneracies more broadly in frustrated magnets.

关键词： NUCLEAR spin MAGNETS THIN films EPITAXY EXCHANGE reactions MAGNETIC moments GROUND state (Quantum mechanics) ELECTRIC distortion

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Electronic transitions in CePd2Si2 studied by resonant x-ray emission spectroscopy at high pressures and low temperatures

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Physical Review B 2012年第23期86卷 235131-235131页

作者： Hitoshi Yamaoka Yumiko Zekko Akio Kotani Ignace Jarrige Naohito Tsujii Jung-Fu Lin Jun'ichiro Mizuki Hideki Abe Hideaki Kitazawa Nozomu Hiraoka Hirofumi Ishii Ku-Ding Tsuei Harima Institute RIKEN (The Institute of Physical and Chemical Research) Sayo Hyogo 679-5148 Japan Graduate School of Science and Technology Kwansei Gakuin University Sanda Hyogo 669-1337 Japan Photon Factory Institute of Materials Structure Science High Energy Accelerator Research Organization 1-1 Oho Tsukuba Ibaraki 305-0801 Japan National Synchrotron Light Source II Brookhaven National Laboratory Upton New York 11973 USA Quantum Beam Center National Institute for Materials Science 1-2-1 Sengen Tsukuba 305-0047 Japan Department of Geological Sciences The University of Texas at Austin Austin Texas 78712 USA National Synchrotron Radiation Research Center Hsinchu 30076 Taiwan

Temperature and pressure dependences of the electronic structure of the heavy-fermion system CePd2Si2 have been investigated using partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Ce L3 edge. The temperature dependence has also been measured for CeRh2Si2 for comparison. In both compounds Ce is in a weakly mixed valence state at ambient pressure, mostly f1 with a small contribution from the f0 component. No temperature dependence of the Ce valence is observed at temperatures as low as 8 K. In CePd2Si2 at 19 K, however, the Ce valence shows a continuous increase with pressure, indicating pressure-induced delocalization of the 4f states. Theoretical calculations based on the single impurity Anderson model reproduce the experimental results well. Pressure dependence of the difference between the ground state valence and the measured valence including the final state effect is also discussed.

关键词： ELECTRONIC structure ABSORPTION spectra X-ray spectroscopy CESIUM compounds CONDUCTION electrons PHYSICS

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Condenser Optics in the X‐ray Microscope

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AIP Conference Proceedings 2011年第1期1365卷 345-348页

作者： H. S. Youn G.‐C. Yin J. C. Andrews P. Pianetta aPohang Accelerator Laboratory Pohang University of Science and Technology 31 San Hyoja‐dong Pohang KyungBuk 790‐784 Korea bNational Synchrotron Radiation Research Center 101 Hsin‐Ann Road Hsinchu 30076 Taiwan cStanford Synchrotron Radiation Light Source SLAC National Accelerator Laboratory 2575 Sand Hill Road Menlo Park CA 94025 USA

Condenser optics focuses x‐rays on a sample position and has a major effect on the exposure time as well as the contrast of a full‐field x‐ray microscope. We have compared two kinds of condenser optics: a capillary...

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Fragile Magnetic Ground State in Half-Doped LaSr2Mn2O7

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Physical Review Letters 2011年第3期107卷 037206-037206页

作者： J.-S. Lee C.-C. Kao C. S. Nelson H. Jang K.-T. Ko S. B. Kim Y. J. Choi S.-W. Cheong S. Smadici P. Abbamonte J.-H. Park Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park California 94025 USA National Synchrotron Light Source Brookhaven National Laboratory Upton New York 11973 USA c-CCMR and Department of Physics Pohang University of Science and Technology Pohang 790-784 South Korea Advancement for College Education Center Konyang University Chungnam 320-711 South Korea R-CEM and Department of Physics and Astronomy Rutgers University Piscataway New Jersey 08854 USA l-PEM and Department of Physics Pohang University of Science and Technology Pohang 790-784 South Korea Physics Department and Frederick Seitz Materials Research Laboratory University of Illinois Urbana Illinois 61801 USA Division of Advanced Materials Science Pohang University of Science and Technology Pohang 790-784 South Korea

We investigated the orbital and antiferromagnetic ordering behaviors of the half-doped bilayer manganite La2−2xSr1+2xMn2O7 (x≃0.5) by using Mn L2,3-edge resonant soft x-ray scattering. Resonant soft x-ray scattering reveals the CE-type orbital order below Too≃220 K, which shows partial melting behavior below Tm≃165 K. We also found coexistence CE- and A-type antiferromagnetic orders. Both orders involve the CE-type orbital order with nearly the same orbital character and are coupled with each other. These results manifest that the ground state with the CE-type antiferromagnetic order is easily susceptible to destabilization into the A-type one even with a small fluctuation of the doping level, as suggested by the extremely narrow magnetic phase boundaries at x≃0.5±0.005.

关键词： X ray scattering

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