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Prasad AK, Šebesta J, Esteban-Puyuelo R, Maldonado P, Ji S, Sanyal B, Grånäs O, Weissenrieder J. Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe. ACS Nano 2023; 17:21006-21017. [PMID: 37862596 PMCID: PMC10655201 DOI: 10.1021/acsnano.3c03827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2023]
Abstract
Thermoelectric materials play a vital role in the pursuit of a sustainable energy system by allowing the conversion of waste heat to electric energy. Low thermal conductivity is essential to achieving high-efficiency conversion. The conductivity depends on an interplay between the phononic and electronic properties of the nonequilibrium state. Therefore, obtaining a comprehensive understanding of nonequilibrium dynamics of the electronic and phononic subsystems as well as their interactions is key for unlocking the microscopic mechanisms that ultimately govern thermal conductivity. A benchmark material that exhibits ultralow thermal conductivity is SnSe. We study the nonequilibrium phonon dynamics induced by an excited electron population using a framework combining ultrafast electron diffuse scattering and nonequilibrium kinetic theory. This in-depth approach provides a fundamental understanding of energy transfer in the spatiotemporal domain. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to nonconservative phonon scattering. The results offer a penetrating perspective on energy transport in condensed matter with far-reaching implications for rational design of advanced materials with tailored thermal properties.
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Affiliation(s)
- Amit Kumar Prasad
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Jakub Šebesta
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Raquel Esteban-Puyuelo
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Pablo Maldonado
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Shaozheng Ji
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Biplab Sanyal
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Oscar Grånäs
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
| | - Jonas Weissenrieder
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
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2
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Kim YJ, Nho HW, Ji S, Lee H, Ko H, Weissenrieder J, Kwon OH. Femtosecond-resolved imaging of a single-particle phase transition in energy-filtered ultrafast electron microscopy. Sci Adv 2023; 9:eadd5375. [PMID: 36706188 PMCID: PMC9882981 DOI: 10.1126/sciadv.add5375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 12/20/2022] [Indexed: 06/18/2023]
Abstract
Using an energy filter in transmission electron microscopy has enabled elemental mapping at the atomic scale and improved the precision of structural determination by gating inelastic and elastic imaging electrons, respectively. Here, we use an energy filter in ultrafast electron microscopy to enhance the temporal resolution toward the domain of atomic motion. Visualizing transient structures with femtosecond temporal precision was achieved by selecting imaging electrons in a narrow energy distribution from dense chirped photoelectron packets with broad longitudinal momentum distributions and thus typically exhibiting picosecond durations. In this study, the heterogeneous ultrafast phase transitions of vanadium dioxide (VO2) nanoparticles, a representative strongly correlated system, were filmed and attributed to the emergence of a transient, low-symmetry metallic phase caused by different local strains. Our approach enables electron microscopy to access the time scale of elementary nuclear motion to visualize the onset of the structural dynamics of matter at the nanoscale.
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Affiliation(s)
- Ye-Jin Kim
- Department of Chemistry, College of Natural Sciences, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
- Center for Soft and Living Matter, Institute for Basic Science, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Hak-Won Nho
- Department of Chemistry, College of Natural Sciences, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
- Center for Soft and Living Matter, Institute for Basic Science, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Shaozheng Ji
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Hyejin Lee
- School of Energy and Chemical Engineering, UNIST, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Hyunhyub Ko
- School of Energy and Chemical Engineering, UNIST, 50 UNIST-gil, Ulsan 44919, Republic of Korea
| | - Jonas Weissenrieder
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Oh-Hoon Kwon
- Department of Chemistry, College of Natural Sciences, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea
- Center for Soft and Living Matter, Institute for Basic Science, 50 UNIST-gil, Ulsan 44919, Republic of Korea
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3
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Ji S, Grånäs O, Kumar Prasad A, Weissenrieder J. Influence of strain on an ultrafast phase transition. Nanoscale 2022; 15:304-312. [PMID: 36484465 PMCID: PMC9773179 DOI: 10.1039/d2nr03395j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
The flexibility of 2D materials combined with properties highly sensitive to strain makes strain engineering a promising avenue for manipulation of both structure and function. Here we investigate the influence of strain, associated with microstructural defects, on a photo-induced structural phase transition in Td-WTe2. Above threshold photoexcitation of uniform, non-strained, samples result in an orthorhombic Td to a metastable orthorhombic 1T* phase transition facilitated by shear displacements of the WTe2 layers along the b axis of the material. In samples prepared with wrinkle defects WTe2 continue its trajectory through a secondary transition that shears the unit cell along the c axis towards a metastable monoclinic 1T' phase. The time scales and microstructural evolution associated with the transition and its subsequent recovery to the 1T* phase is followed in detail by a combination of ultrafast electron diffraction and microscopy. Our findings show how local strain fields can be employed for tailoring phase change dynamics in ultrafast optically driven processes with potential applications in phase change devices.
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Affiliation(s)
- Shaozheng Ji
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
- Ultrafast Electron Microscopy Laboratory, The MOE Key Laboratory of Weak-Light Nonlinear Photonics, School of Physics, Nankai University, Tianjin 300071, China
| | - Oscar Grånäs
- Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Amit Kumar Prasad
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
| | - Jonas Weissenrieder
- Materials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
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4
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Guo Q, Dendzik M, Grubišić-Čabo A, Berntsen MH, Li C, Chen W, Matta B, Starke U, Hessmo B, Weissenrieder J, Tjernberg O. A narrow bandwidth extreme ultra-violet light source for time- and angle-resolved photoemission spectroscopy. Struct Dyn 2022; 9:024304. [PMID: 35540107 PMCID: PMC9054270 DOI: 10.1063/4.0000149] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Accepted: 04/06/2022] [Indexed: 06/01/2023]
Abstract
Here, we present a high repetition rate, narrow bandwidth, extreme ultraviolet photon source for time- and angle-resolved photoemission spectroscopy. The narrow bandwidth pulses Δ E = 9 , 14 , and 18 meV for photon energies h ν = 10.8 , 18.1 , and 25.3 eV are generated through high harmonic generation using ultra-violet drive pulses with relatively long pulse lengths (461 fs). The high harmonic generation setup employs an annular drive beam in tight focusing geometry at a repetition rate of 250 kHz. Photon energy selection is provided by a series of selectable multilayer bandpass mirrors and thin film filters, thus avoiding any time broadening introduced by single grating monochromators. A two stage optical-parametric amplifier provides < 100 fs tunable pump pulses from 0.65 μm to 9 μm. The narrow bandwidth performance of the light source is demonstrated through angle-resolved photoemission measurements on a series of quantum materials, including high-temperature superconductor Bi-2212, WSe2, and graphene.
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Affiliation(s)
- Qinda Guo
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Maciej Dendzik
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Antonija Grubišić-Čabo
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Magnus H. Berntsen
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Cong Li
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Wanyu Chen
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Bharti Matta
- Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
| | - Ulrich Starke
- Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
| | - Björn Hessmo
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Jonas Weissenrieder
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - Oscar Tjernberg
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
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5
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Ji S, Grånäs O, Weissenrieder J. Manipulation of Stacking Order in Td-WTe 2 by Ultrafast Optical Excitation. ACS Nano 2021; 15:8826-8835. [PMID: 33913693 PMCID: PMC8291768 DOI: 10.1021/acsnano.1c01301] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 04/27/2021] [Indexed: 06/12/2023]
Abstract
Subtle changes in stacking order of layered transition metal dichalcogenides may have profound influence on the electronic and optical properties. The intriguing electronic properties of Td-WTe2 can be traced to the break of inversion symmetry resulting from the ground-state stacking sequence. Strategies for perturbation of the stacking order are actively pursued for intentional tuning of material properties, where optical excitation is of specific interest since it holds the potential for integration of ultrafast switches in future device designs. Here we investigate the structural response in Td-WTe2 following ultrafast photoexcitation by time-resolved electron diffraction. A 0.23 THz shear phonon, involving layer displacement along the b axis, was excited by a 515 nm laser pulse. Pump fluences in excess of a threshold of ∼1 mJ/cm2 result in formation, with an ∼5 ps time constant, of a new stacking order by layer displacement along the b axis in the direction toward the centrosymmetric 1T* phase. The shear displacement of the layers increases with pump fluence until saturation at ∼8 pm. We demonstrate that the excitation of the shear phonon and the stabilization of the metastable phase are decoupled when using an optical pump as evidenced by observation of a transition also in samples with a pinned shear phonon. The results are compared to dynamic first-principles simulations and the transition is interpreted in terms of a mechanism where transient local disorder is prominent before settling at the atomic positions of the metastable phase. This interpretation is corroborated by results from diffuse scattering. The correlation between excitation of intralayer vibrations and interlayer interaction demonstrates the importance of including both short- and long-range interactions in an accurate description of how optical fields can be employed to manipulate the stacking order in 2-dimensional transition metal dichalcogenides.
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Affiliation(s)
- Shaozheng Ji
- Materials
and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
| | - Oscar Grånäs
- Division
for Materials Theory, Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden
| | - Jonas Weissenrieder
- Materials
and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
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6
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Zhu S, Scardamaglia M, Kundsen J, Sankari R, Tarawneh H, Temperton R, Pickworth L, Cavalca F, Wang C, Tissot H, Weissenrieder J, Hagman B, Gustafson J, Kaya S, Lindgren F, Källquist I, Maibach J, Hahlin M, Boix V, Gallo T, Rehman F, D’Acunto G, Schnadt J, Shavorskiy A. HIPPIE: a new platform for ambient-pressure X-ray photoelectron spectroscopy at the MAX IV Laboratory. J Synchrotron Radiat 2021; 28:624-636. [PMID: 33650575 PMCID: PMC7941293 DOI: 10.1107/s160057752100103x] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2020] [Accepted: 01/28/2021] [Indexed: 05/28/2023]
Abstract
HIPPIE is a soft X-ray beamline on the 3 GeV electron storage ring of the MAX IV Laboratory, equipped with a novel ambient-pressure X-ray photoelectron spectroscopy (APXPS) instrument. The endstation is dedicated to performing in situ and operando X-ray photoelectron spectroscopy experiments in the presence of a controlled gaseous atmosphere at pressures up to 30 mbar [1 mbar = 100 Pa] as well as under ultra-high-vacuum conditions. The photon energy range is 250 to 2200 eV in planar polarization and with photon fluxes >1012 photons s-1 (500 mA ring current) at a resolving power of greater than 10000 and up to a maximum of 32000. The endstation currently provides two sample environments: a catalysis cell and an electrochemical/liquid cell. The former allows APXPS measurements of solid samples in the presence of a gaseous atmosphere (with a mixture of up to eight gases and a vapour of a liquid) and simultaneous analysis of the inlet/outlet gas composition by online mass spectrometry. The latter is a more versatile setup primarily designed for APXPS at the solid-liquid (dip-and-pull setup) or liquid-gas (liquid microjet) interfaces under full electrochemical control, and it can also be used as an open port for ad hoc-designed non-standard APXPS experiments with different sample environments. The catalysis cell can be further equipped with an IR reflection-absorption spectrometer, allowing for simultaneous APXPS and IR spectroscopy of the samples. The endstation is set up to easily accommodate further sample environments.
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Affiliation(s)
- Suyun Zhu
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
| | | | - Jan Kundsen
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Rami Sankari
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
- Department of Physics, Tampere University of Technology, PO Box 692, FIN-33101 Tampere, Finland
| | - Hamed Tarawneh
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
| | - Robert Temperton
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
| | - Louisa Pickworth
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
| | - Filippo Cavalca
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
| | - Chunlei Wang
- Material Physics, School of Engineering Sciences, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
| | - Héloïse Tissot
- Material Physics, School of Engineering Sciences, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
| | - Jonas Weissenrieder
- Material Physics, School of Engineering Sciences, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
| | - Benjamin Hagman
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Johan Gustafson
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Sarp Kaya
- Department of Chemistry, Koc University, Istanbul 34450, Turkey
| | - Fredrik Lindgren
- Department of Physics and Astronomy, Division of Molecular and Condensed Matter Physics, Uppsala University, 751 20 Uppsala, Sweden
| | - Ida Källquist
- Department of Physics and Astronomy, Division of Molecular and Condensed Matter Physics, Uppsala University, 751 20 Uppsala, Sweden
| | - Julia Maibach
- Institute for Applied Materials, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Maria Hahlin
- Department of Physics and Astronomy, Division of Molecular and Condensed Matter Physics, Uppsala University, 751 20 Uppsala, Sweden
- Department of Chemistry – Ångström Laboratory, Uppsala University, Box 538, 751 21 Uppsala, Sweden
| | - Virginia Boix
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Tamires Gallo
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Foqia Rehman
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Giulio D’Acunto
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
| | - Joachim Schnadt
- MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
- Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
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Abstract
Manipulation and detection of spins at the nanoscale is of considerable contemporary interest as it may not only facilitate a description of fundamental physical processes but also plays a critical role in the development of spintronic devices. Here, we describe the application of a novel combination of transient grating excitation with Lorentz ultrafast electron microscopy to control and detect magnetization dynamics with combined nanometer and picosecond resolutions. Excitation of Ni80Fe20 thin film samples results in the formation of transient coherently precessing magnetic gratings. From the time-resolved results, we extract detailed real space information of the magnetic precession, including local magnetization, precession frequency, and relevant decay factors. The Lorentz contrast of the dynamics is sensitive to the alignment of the in-plane components of the applied field. The experimental results are rationalized by a model considering local demagnetization and the phase of the precessing magnetic moments. We envision that this technique can be extended to the study of spin waves and dynamic behavior in ferrimagnetic and antiferromagnetic systems.
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Affiliation(s)
- Gaolong Cao
- Materials and Nano Physics, Department of Applied Physics, KTH Royal Institute of Technology, Kista, Sweden. and Department of Physics, University of Gothenburg, Gothenburg, Sweden.
| | - Sheng Jiang
- Department of Physics, University of Gothenburg, Gothenburg, Sweden.
| | - Johan Åkerman
- Materials and Nano Physics, Department of Applied Physics, KTH Royal Institute of Technology, Kista, Sweden. and Department of Physics, University of Gothenburg, Gothenburg, Sweden.
| | - Jonas Weissenrieder
- Materials and Nano Physics, Department of Applied Physics, KTH Royal Institute of Technology, Kista, Sweden.
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8
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Abstract
Single-atom catalysts have recently been subject to considerable attention within applied catalysis. However, complications in the preparation of well-defined single-atom model systems have hampered efforts to determine the reaction mechanisms underpinning the reported activity. By means of an atomic layer deposition method utilizing the steric hindrance of the ligands, isolated Fe1O3 motifs were grown on a single-crystal Cu2O(100) surface at densities up to 0.21 sites per surface unit cell. Ambient pressure X-ray photoelectron spectroscopy shows a strong metal-support interaction with Fe in a chemical state close to 3+. Results from scanning tunneling microscopy and density functional calculations demonstrate that isolated Fe1O3 is exclusively formed and occupies a single site per surface unit cell, coordinating to two oxygen atoms from the Cu2O lattice and another through abstraction from O2. The isolated Fe1O3 motif is active for CO oxidation at 473 K. The growth method holds promise for extension to other catalytic systems.
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Affiliation(s)
- Chunlei Wang
- Material Physics, School of Engineering Sciences , KTH Royal Institute of Technology , SE-100 44 Stockholm , Sweden
| | - Heloise Tissot
- Material Physics, School of Engineering Sciences , KTH Royal Institute of Technology , SE-100 44 Stockholm , Sweden
| | - Joakim Halldin Stenlid
- Department of Physics, Albanova University Center , Stockholm University , SE-106 91 Stockholm , Sweden
- Applied Physical Chemistry, Department of Chemistry , KTH Royal Institute of Technology , SE-100 44 Stockholm , Sweden
| | - Sarp Kaya
- Koç University TUPRAS Energy Center , 34450 Istanbul , Turkey
- Chemistry Department , Koç University , 34450 Istanbul , Turkey
| | - Jonas Weissenrieder
- Material Physics, School of Engineering Sciences , KTH Royal Institute of Technology , SE-100 44 Stockholm , Sweden
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10
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Ji S, Piazza L, Cao G, Park ST, Reed BW, Masiel DJ, Weissenrieder J. Influence of cathode geometry on electron dynamics in an ultrafast electron microscope. Struct Dyn 2017; 4:054303. [PMID: 28781982 PMCID: PMC5515673 DOI: 10.1063/1.4994004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 07/03/2017] [Indexed: 06/01/2023]
Abstract
Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.
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Affiliation(s)
- Shaozheng Ji
- KTH Royal Institute of Technology, Material Physics, Electrum 229, SE-16440 Kista, Sweden
| | - Luca Piazza
- KTH Royal Institute of Technology, Material Physics, Electrum 229, SE-16440 Kista, Sweden
| | - Gaolong Cao
- KTH Royal Institute of Technology, Material Physics, Electrum 229, SE-16440 Kista, Sweden
| | - Sang Tae Park
- Integrated Dynamic Electron Solutions, Inc. (IDES), Pleasanton, California 94588, USA
| | - Bryan W Reed
- Integrated Dynamic Electron Solutions, Inc. (IDES), Pleasanton, California 94588, USA
| | - Daniel J Masiel
- Integrated Dynamic Electron Solutions, Inc. (IDES), Pleasanton, California 94588, USA
| | - Jonas Weissenrieder
- KTH Royal Institute of Technology, Material Physics, Electrum 229, SE-16440 Kista, Sweden
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11
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Besharat Z, Halldin Stenlid J, Soldemo M, Marks K, Önsten A, Johnson M, Öström H, Weissenrieder J, Brinck T, Göthelid M. Dehydrogenation of methanol on Cu 2O(100) and (111). J Chem Phys 2017; 146:244702. [PMID: 28668016 DOI: 10.1063/1.4989472] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Adsorption and desorption of methanol on the (111) and (100) surfaces of Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surface oxygen.
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Affiliation(s)
- Zahra Besharat
- Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden
| | - Joakim Halldin Stenlid
- Applied Physical Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, S-100 44 Stockholm, Sweden
| | - Markus Soldemo
- Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden
| | - Kess Marks
- Department of Physics, Stockholm University, S-106 91 Stockholm, Sweden
| | - Anneli Önsten
- Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden
| | - Magnus Johnson
- Division of Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology, Stockholm S-100 44, Sweden
| | - Henrik Öström
- Department of Physics, Stockholm University, S-106 91 Stockholm, Sweden
| | - Jonas Weissenrieder
- Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden
| | - Tore Brinck
- Applied Physical Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, S-100 44 Stockholm, Sweden
| | - Mats Göthelid
- Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden
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12
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Törne K, Örnberg A, Weissenrieder J. Influence of strain on the corrosion of magnesium alloys and zinc in physiological environments. Acta Biomater 2017; 48:541-550. [PMID: 27780765 DOI: 10.1016/j.actbio.2016.10.030] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 10/04/2016] [Accepted: 10/22/2016] [Indexed: 10/20/2022]
Abstract
During implantation load-bearing devices experience stress that may influence its mechanical and corrosion profile and potentially lead to premature rupture. The susceptibility to stress corrosion cracking (SCC) of the Mg-Al alloy AZ61 and Zn was studied in simulated body fluid (m-SBF) and whole blood by slow strain rate (SSR) testing in combination with electrochemical impedance spectroscopy (EIS) and further ex situ analysis including scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy. AZ61 was found to be highly susceptible to SCC. EIS analysis show that although the majority of cracking occurred during the apparent plastic straining, cracking initiation occurs already in the elastic region at ∼50% of the ultimate tensile strength (UTS). Shifts in EIS phase angle and open circuit potential can be used to detect the onset of SCC. Zinc demonstrated a highly ductile behavior with limited susceptibility to SCC. No significant decrease in UTS was observed in m-SBF but a decrease in time to failure by ∼25% compared to reference samples indicates some effect on the mechanical properties during the ductile straining. The formation of micro cracks, ∼10μm deep, was indicated by the EIS analysis and later confirmed by ex situ SEM. The results of SSR analysis of zinc in whole blood showed a reduced effect compared to m-SBF and no cracks were detected. It appears that formation of an organic surface layer protects the corroding surface from cracking. These results highlight the importance of considering the effect of biological species on the degradation of implants in the clinical situation. STATEMENT OF SIGNIFICANCE Strain may deteriorate the corrosion properties of metallic implants drastically. We study the influence of load on the corrosion properties of a magnesium alloy and zinc by a combination of electrochemical impedance spectroscopy (EIS) and slow strain rate analysis. This combination of techniques has previously not been used for studying degradation in physiological relevant electrolytes. EIS provide valuable information on the initial formation of cracks, detecting crack nucleation before feasible in slow strain rate analysis. This sensitivity of EIS shows the potential for electrochemical methods to be used for in situ monitoring crack formation of implants in more applied studies.
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Törne K, Örnberg A, Weissenrieder J. The influence of buffer system and biological fluids on the degradation of magnesium. J Biomed Mater Res B Appl Biomater 2016; 105:1490-1502. [PMID: 27098550 DOI: 10.1002/jbm.b.33685] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 03/22/2016] [Accepted: 03/29/2016] [Indexed: 01/25/2023]
Affiliation(s)
- Karin Törne
- Materials and Nano Physics; KTH Royal Institute of Technology; Electrum 229 16440 Kista Sweden
- St. Jude Medical; 177 East County Road B St. Paul MN 55117 USA
| | - Andreas Örnberg
- St. Jude Medical; 177 East County Road B St. Paul MN 55117 USA
| | - Jonas Weissenrieder
- Materials and Nano Physics; KTH Royal Institute of Technology; Electrum 229 16440 Kista Sweden
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Stenlid JH, Soldemo M, Johansson AJ, Leygraf C, Göthelid M, Weissenrieder J, Brinck T. Reactivity at the Cu2O(100):Cu–H2O interface: a combined DFT and PES study. Phys Chem Chem Phys 2016; 18:30570-30584. [DOI: 10.1039/c6cp04410g] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Detailed characterization of the structure and composition of the water–cuprite interface.
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Affiliation(s)
- J. H. Stenlid
- Applied Physical Chemistry
- School of Chemical Science and Engineering
- KTH Royal Institute of Technology
- SE-100 44 Stockholm
- Sweden
| | - M. Soldemo
- Material Physics, KTH Royal Institute of Technology
- SE-164 40 Kista
- Sweden
| | - A. J. Johansson
- Swedish Nuclear Fuel and Waste Management Co (SKB)
- Stockholm
- Sweden
| | - C. Leygraf
- Surface and Corrosion Science
- School of Chemical Science and Engineering
- KTH Royal Institute of Technology
- SE-100 44 Stockholm
- Sweden
| | - M. Göthelid
- Material Physics, KTH Royal Institute of Technology
- SE-164 40 Kista
- Sweden
| | - J. Weissenrieder
- Material Physics, KTH Royal Institute of Technology
- SE-164 40 Kista
- Sweden
| | - T. Brinck
- Applied Physical Chemistry
- School of Chemical Science and Engineering
- KTH Royal Institute of Technology
- SE-100 44 Stockholm
- Sweden
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Törne K, Larsson M, Norlin A, Weissenrieder J. Degradation of zinc in saline solutions, plasma, and whole blood. J Biomed Mater Res B Appl Biomater 2015; 104:1141-51. [PMID: 26061136 DOI: 10.1002/jbm.b.33458] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Revised: 04/30/2015] [Accepted: 05/13/2015] [Indexed: 11/08/2022]
Abstract
The initial degradation of zinc has been investigated through exposures to simulated and real body fluids of increasing complexity: phosphate buffered saline (PBS), Ringer's saline solution, human plasma, and whole blood. Real body fluids were used to close the electrolyte gap between simulated and in vivo environment. Polarization of zinc in whole blood show a passive response not present in other electrolytes. The analysis shows a decrease in corrosion rate with time for plasma and whole blood and an increase for PBS and Ringer's. During exposure to plasma and whole blood a bi-layered corrosion product with poor adherence was formed over a uniformly corroding surface. The corrosion products comprise a mixture of inorganic material and biomolecules. Samples degrading in PBS were prone to localized corrosion and formed thick porous corrosion products of primarily zinc phosphates while in Ringer's solution a gel like layer of zinc carbonate was formed over an interface with shallow pits. The use of whole blood or plasma as electrolytes for short term in vitro evaluation of potential biodegradable metals may provide an improved understanding of the behavior in vivo, while Ringer's solution is preferred over PBS for long term degradation studies of zinc. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1141-1151, 2016.
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Affiliation(s)
- Karin Törne
- Material Physics, KTH Royal Institute of Technology, Electrum 229, 16440, Kista, Sweden.,St Jude Medical Systems AB, Palmbladsgatan, Uppsala, Sweden
| | - Mariann Larsson
- Material Physics, KTH Royal Institute of Technology, Electrum 229, 16440, Kista, Sweden
| | - Anna Norlin
- St Jude Medical Systems AB, Palmbladsgatan, Uppsala, Sweden
| | - Jonas Weissenrieder
- Material Physics, KTH Royal Institute of Technology, Electrum 229, 16440, Kista, Sweden
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Affiliation(s)
| | - Johan Gustafson
- Division of Synchrotron Radiation Research; Lund University; 221 00 Lund Sweden
| | - Dario Stacchiola
- Chemistry Department; Brookhaven National Laboratory; Upton NY 11973 USA
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17
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An W, Baber AE, Xu F, Soldemo M, Weissenrieder J, Stacchiola D, Liu P. Mechanistic Study of CO Titration on CuxO/Cu(1 1 1) (x≤2) Surfaces. ChemCatChem 2014. [DOI: 10.1002/cctc.201402177] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Baber AE, Yang X, Kim HY, Mudiyanselage K, Soldemo M, Weissenrieder J, Senanayake SD, Al-Mahboob A, Sadowski JT, Evans J, Rodriguez JA, Liu P, Hoffmann FM, Chen JG, Stacchiola DJ. Stabilization of Catalytically Active Cu+Surface Sites on Titanium-Copper Mixed-Oxide Films. Angew Chem Int Ed Engl 2014; 53:5336-40. [DOI: 10.1002/anie.201402435] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Indexed: 11/06/2022]
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Baber AE, Yang X, Kim HY, Mudiyanselage K, Soldemo M, Weissenrieder J, Senanayake SD, Al-Mahboob A, Sadowski JT, Evans J, Rodriguez JA, Liu P, Hoffmann FM, Chen JG, Stacchiola DJ. Stabilization of Catalytically Active Cu+Surface Sites on Titanium-Copper Mixed-Oxide Films. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201402435] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Baber AE, Xu F, Dvorak F, Mudiyanselage K, Soldemo M, Weissenrieder J, Senanayake SD, Sadowski JT, Rodriguez JA, Matolín V, White MG, Stacchiola DJ. In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer. J Am Chem Soc 2013; 135:16781-4. [DOI: 10.1021/ja408506y] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
| | - Fang Xu
- Stony Brook University, Stony
Brook, New York 11794, United States
| | - Filip Dvorak
- Faculty of Mathematics and Physics, Charles University, Department of Surface and Plasma Science, Prague, Czech Republic
| | | | - Markus Soldemo
- KTH Royal Institute of Technology, Material
Physics, Stockholm, Sweden
| | | | | | | | | | - Vladimír Matolín
- Faculty of Mathematics and Physics, Charles University, Department of Surface and Plasma Science, Prague, Czech Republic
| | - Michael G. White
- Stony Brook University, Stony
Brook, New York 11794, United States
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Martynova Y, Soldemo M, Weissenrieder J, Sachert S, Polzin S, Widdra W, Shaikhutdinov S, Freund HJ. CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111). Catal Letters 2013. [DOI: 10.1007/s10562-013-1117-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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22
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Göthelid M, Tymczenko M, Chow W, Ahmadi S, Yu S, Bruhn B, Stoltz D, von Schenck H, Weissenrieder J, Sun C. Surface concentration dependent structures of iodine on Pd(110). J Chem Phys 2012. [DOI: 10.1063/1.4768165] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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23
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Gustafsson O, Karim A, Berggren J, Wang Q, Reuterskiöld-Hedlund C, Ernerheim-Jokumsen C, Soldemo M, Weissenrieder J, Persson S, Almqvist S, Ekenberg U, Noharet B, Asplund C, Göthelid M, Andersson JY, Hammar M. Photoluminescence and photoresponse from InSb/InAs-based quantum dot structures. Opt Express 2012; 20:21264-21271. [PMID: 23037249 DOI: 10.1364/oe.20.021264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
InSb-based quantum dots grown by metal-organic vapor-phase epitaxy (MOVPE) on InAs substrates are studied for use as the active material in interband photon detectors. Long-wavelength infrared (LWIR) photoluminescence is demonstrated with peak emission at 8.5 µm and photoresponse, interpreted to originate from type-II interband transitions in a p-i-n photodiode, was measured up to 6 µm, both at 80 K. The possibilities and benefits of operation in the LWIR range (8-12 µm) are discussed and the results suggest that InSb-based quantum dot structures can be suitable candidates for photon detection in the LWIR regime.
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Affiliation(s)
- Oscar Gustafsson
- KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden.
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Yu S, Ahmadi S, Zuleta M, Tian H, Schulte K, Pietzsch A, Hennies F, Weissenrieder J, Yang X, Göthelid M. Adsorption geometry, molecular interaction, and charge transfer of triphenylamine-based dye on rutile TiO2(110). J Chem Phys 2010; 133:224704. [DOI: 10.1063/1.3509389] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Lindner B, Curtis M, Weissenrieder J, Schwab M. Headspace Moisture Analysis in Medical Device Packages. J Med Device 2008. [DOI: 10.1115/1.2927393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Moisture levels in medical device packages influence a variety of crucial device properties, e.g. mechanical properties, corrosion and leach rates, drug potency, and ultimately shelf life. This is especially true for drug releasing and biodegradable device materials. It is therefore important to establish a high degree of control and accuracy of the humidity levels at all relevant stages in the production process as well as in the final package. In the current study we demonstrate a newly developed method for accurate headspace moisture trace level analysis in medical device packages using extractive gas phase Fourier transform infrared (FTIR) spectroscopy. Volumetric aliquots were extracted, using a specially designed extraction assembly, from the headspace of medical device relevant packages. The headspace water concentration was analyzed using a validated gas phase FTIR system1. Water bands in the spectral region 1600–2200cm 1 were chosen for the quantitative analysis. Sample spectra were compared, with a least square fit procedure, to water reference spectra at known concentration. Accurate quantification was demonstrated for headspace water vapor concentrations less than 100ppm. This is considerably lower than feasible with conventional package headspace moisture analysis techniques. The results of this study demonstrate the benefits of using extractive gas phase FTIR for low level moisture analysis of small headspace volumes.
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Baraldi A, Vesselli E, Bianchettin L, Comelli G, Lizzit S, Petaccia L, de Gironcoli S, Locatelli A, Mentes TO, Aballe L, Weissenrieder J, Andersen JN. The (1×1)→hexagonal structural transition on Pt(100) studied by high-energy resolution core level photoemission. J Chem Phys 2007; 127:164702. [DOI: 10.1063/1.2794344] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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27
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Lobastov VA, Weissenrieder J, Tang J, Zewail AH. Ultrafast electron microscopy (UEM): four-dimensional imaging and diffraction of nanostructures during phase transitions. Nano Lett 2007; 7:2552-8. [PMID: 17622175 DOI: 10.1021/nl071341e] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Four-dimensional (4D) imaging during structural changes are reported here using ultrafast electron microscopy (UEM). For nanostructures, the phase transition in the strongly correlated material vanadium dioxide is our case study. The transition is initiated and probed in situ, in the microscope, by a femtosecond near-infrared and electron pulses (at 120 keV). Real-space imaging and Fourier-space diffraction patterns show that the transition from the monoclinic (P21/c) to tetragonal (P42/mnm) structure is induced in 3 +/- 1 ps, but there exists a nonequilibrium (metastable) structure whose nature is determined by electronic, carrier-induced, structural changes. For the particles studied, the subsequent recovery occurs in about 1 ns. Because of the selectivity of excitation from the 3d parallel-band, and the relatively low fluence used, these results show the critical role of carriers in weakening the V4+-V4+ bonding in the monoclinic phase and the origin of the nonequilibrium phase. A theoretical two-dimensional (2D) diffusion model for nanoscale materials is presented, and its results account for the observed behavior.
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Affiliation(s)
- Vladimir A Lobastov
- Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
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Sierka M, Todorova TK, Sauer J, Kaya S, Stacchiola D, Weissenrieder J, Shaikhutdinov S, Freund HJ. Oxygen adsorption on Mo(112) surface studied by ab initio genetic algorithm and experiment. J Chem Phys 2007; 126:234710. [PMID: 17600438 DOI: 10.1063/1.2743427] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Density functional theory in combination with genetic algorithm is applied to determine the atomic models of p(1x2) and p(1x3) surface structures observed upon oxygen adsorption on a Mo(112) surface. The authors' simulations reveal an unusual flexibility of Mo(112) resulting in oxygen-induced reconstructions and lead to more stable structures than any suggested so far. Comparison of the stabilities of the predicted models shows that different p(1x2) and p(1x3) structures may coexist over a wide range of oxygen pressures. A pure p(1x2) structure can be obtained only in a narrow region of oxygen pressures. In contrast, a pure p(1x3) structure cannot exist as a stable phase. The results of simulations are fully supported by a multitude of experimental data obtained from low energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy.
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Affiliation(s)
- Marek Sierka
- Institut für Chemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany.
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Abstract
Reported here is direct imaging (and diffraction) by using 4D ultrafast electron microscopy (UEM) with combined spatial and temporal resolutions. In the first phase of UEM, it was possible to obtain snapshot images by using timed, single-electron packets; each packet is free of space-charge effects. Here, we demonstrate the ability to obtain sequences of snapshots ("movies") with atomic-scale spatial resolution and ultrashort temporal resolution. Specifically, it is shown that ultrafast metal-insulator phase transitions can be studied with these achieved spatial and temporal resolutions. The diffraction (atomic scale) and images (nanometer scale) we obtained manifest the structural phase transition with its characteristic hysteresis, and the time scale involved (100 fs) is now studied by directly monitoring coordinates of the atoms themselves.
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Affiliation(s)
- Michael S. Grinolds
- Physical Biology Center for Ultrafast Science and Technology, California Institute of Technology, Pasadena, CA 91125
| | - Vladimir A. Lobastov
- Physical Biology Center for Ultrafast Science and Technology, California Institute of Technology, Pasadena, CA 91125
| | - Jonas Weissenrieder
- Physical Biology Center for Ultrafast Science and Technology, California Institute of Technology, Pasadena, CA 91125
| | - Ahmed H. Zewail
- Physical Biology Center for Ultrafast Science and Technology, California Institute of Technology, Pasadena, CA 91125
- To whom correspondence should be addressed.
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Stacchiola D, Kaya S, Weissenrieder J, Kuhlenbeck H, Shaikhutdinov S, Freund HJ, Sierka M, Todorova TK, Sauer J. Synthesis and Structure of Ultrathin Aluminosilicate Films. Angew Chem Int Ed Engl 2006; 45:7636-9. [PMID: 17051629 DOI: 10.1002/anie.200602670] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Dario Stacchiola
- Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
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31
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Stacchiola D, Kaya S, Weissenrieder J, Kuhlenbeck H, Shaikhutdinov S, Freund HJ, Sierka M, Todorova TK, Sauer J. Synthese und Struktur eines ultradünnen Alumosilicatfilms. Angew Chem Int Ed Engl 2006. [DOI: 10.1002/ange.200602670] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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32
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Sierka M, Todorova TK, Kaya S, Stacchiola D, Weissenrieder J, Lu J, Gao H, Shaikhutdinov S, Freund HJ, Sauer J. Interplay between theory and experiment in the quest for silica with reduced dimensionality grown on a Mo(112) surface. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.04.072] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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33
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Wang JG, Li WX, Borg M, Gustafson J, Mikkelsen A, Pedersen TM, Lundgren E, Weissenrieder J, Klikovits J, Schmid M, Hammer B, Andersen JN. One-dimensional PtO2 at Pt steps: formation and reaction with CO. Phys Rev Lett 2005; 95:256102. [PMID: 16384475 DOI: 10.1103/physrevlett.95.256102] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Indexed: 05/05/2023]
Abstract
Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of the Pt(332) surface after exposure. The 1D oxide is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, and is therefore argued to be a precursor to the Pt oxidation. As an example of the consequences of such a precursor exclusively present at the steps, we investigate the reaction of CO with oxygen covered Pt(332). Albeit more strongly bound, the oxidic oxygen is found to react more easily with CO than oxygen chemisorbed on the Pt terraces.
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Affiliation(s)
- J G Wang
- Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
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Weissenrieder J, Kaya S, Lu JL, Gao HJ, Shaikhutdinov S, Freund HJ, Sierka M, Todorova TK, Sauer J. Atomic structure of a thin silica film on a Mo(112) substrate: a two-dimensional network of SiO4 tetrahedra. Phys Rev Lett 2005; 95:076103. [PMID: 16196802 DOI: 10.1103/physrevlett.95.076103] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Indexed: 05/04/2023]
Abstract
The structure of a thin single crystalline SiO(2) film grown on Mo(112) has been studied by scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. In excellent agreement with the experimental results, density functional theory calculations show that the film consists of a two-dimensional network of corner sharing [SiO(4)] tetrahedra, with one oxygen of each tetrahedron binding to the protruding Mo atoms of the Mo(112) surface.
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Affiliation(s)
- J Weissenrieder
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
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Weissenrieder J, Mikkelsen A, Andersen JN, Feibelman PJ, Held G. Experimental evidence for a partially dissociated water bilayer on Ru[0001]. Phys Rev Lett 2004; 93:196102. [PMID: 15600854 DOI: 10.1103/physrevlett.93.196102] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2004] [Indexed: 05/24/2023]
Abstract
Core-level photoelectron spectra, in excellent agreement with ab initio calculations, confirm that the stable wetting layer of water on Ru[0001] contains O-H and H2O in roughly 3:5 proportion, for OHx coverages between 0.25 and 0.7 ML, and T<170 K. Proton disorder explains why the wetting structure looks to low energy electron diffraction (LEED) to be an ordered p(square root of 3 x square root of 3)R30 degrees adlayer, even though approximately 3/8 of its molecules are dissociated. Complete dissociation to atomic oxygen starts near 190 K. Low photon flux in the synchrotron experiments ensured that the diagnosis of the nature of the wetting structure quantified by LEED is free of beam-induced damage.
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