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Yang B, Ji Q, Huang FZ, Li J, Tian YZ, Xue B, Zhu R, Wu H, Yang H, Yang YB, Tang S, Zhao HB, Cao Y, Du J, Wang BG, Zhang C, Wu D. Picosecond Spin Current Generation from Vicinal Metal-Antiferromagnetic Insulator Interfaces. PHYSICAL REVIEW LETTERS 2024; 132:176703. [PMID: 38728713 DOI: 10.1103/physrevlett.132.176703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 03/22/2024] [Indexed: 05/12/2024]
Abstract
We report the picosecond spin current generation from the interface between a heavy metal and a vicinal antiferromagnet insulator Cr_{2}O_{3} by laser pulses at room temperature and zero magnetic field. It is converted into a detectable terahertz emission in the heavy metal via the inverse spin Hall effect. The vicinal interfaces are apparently the source of the picosecond spin current, as evidenced by the proportional terahertz signals to the vicinal angle. We attribute the origin of the spin current to the transient magnetic moment generated by an interfacial nonlinear magnetic-dipole difference-frequency generation. We propose a model based on the in-plane inversion symmetry breaking to quantitatively explain the terahertz intensity with respect to the angles of the laser polarization and the film azimuth. Our work opens new opportunities in antiferromagnetic and ultrafast spintronics by considering symmetry breaking.
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Affiliation(s)
- B Yang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Qing Ji
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - F Z Huang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Jiacong Li
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Y Z Tian
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - B Xue
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Ruxian Zhu
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Hui Wu
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Hanyue Yang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Y B Yang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Shaolong Tang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - H B Zhao
- Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433, People's Republic of China
| | - Y Cao
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - J Du
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - B G Wang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
| | - D Wu
- National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
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Schreck S, Diesen E, Dell'Angela M, Liu C, Weston M, Capotondi F, Ogasawara H, LaRue J, Costantini R, Beye M, Miedema PS, Halldin Stenlid J, Gladh J, Liu B, Wang HY, Perakis F, Cavalca F, Koroidov S, Amann P, Pedersoli E, Naumenko D, Nikolov I, Raimondi L, Abild-Pedersen F, Heinz TF, Voss J, Luntz AC, Nilsson A. Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-Ray Spectroscopy. PHYSICAL REVIEW LETTERS 2022; 129:276001. [PMID: 36638285 DOI: 10.1103/physrevlett.129.276001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 06/14/2022] [Accepted: 11/18/2022] [Indexed: 06/17/2023]
Abstract
The electronic excitation occurring on adsorbates at ultrafast timescales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) of a simple well-known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel [Ni(100)] surface, following intense laser optical pumping at 400 nm. We observe ultrafast (∼100 fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.
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Affiliation(s)
- Simon Schreck
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Elias Diesen
- SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | | | - Chang Liu
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Matthew Weston
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Flavio Capotondi
- FERMI, Elettra-Sincrotrone Trieste, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - Hirohito Ogasawara
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Jerry LaRue
- Schmid College of Science and Technology, Chapman University, Orange, California 92866, USA
| | - Roberto Costantini
- CNR-IOM, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
- Physics Department, University of Trieste, Via Valerio 2, 34127 Trieste, Italy
| | - Martin Beye
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg 22607, Germany
| | - Piter S Miedema
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg 22607, Germany
| | - Joakim Halldin Stenlid
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
- SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Jörgen Gladh
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Boyang Liu
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Hsin-Yi Wang
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Fivos Perakis
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Filippo Cavalca
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Sergey Koroidov
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Peter Amann
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
| | - Emanuele Pedersoli
- FERMI, Elettra-Sincrotrone Trieste, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - Denys Naumenko
- FERMI, Elettra-Sincrotrone Trieste, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - Ivaylo Nikolov
- FERMI, Elettra-Sincrotrone Trieste, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - Lorenzo Raimondi
- FERMI, Elettra-Sincrotrone Trieste, SS 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - Frank Abild-Pedersen
- SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Tony F Heinz
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Johannes Voss
- SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Alan C Luntz
- SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Anders Nilsson
- Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
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Pustovalov VK. Multi-temperature modeling of femtosecond laser pulse on metallic nanoparticles accounting for the temperature dependences of the parameters. NANOTECHNOLOGY AND PRECISION ENGINEERING 2022. [DOI: 10.1063/10.0013776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
This review considers the fundamental dynamical processes of metal nanoparticles during and after the impact of a femtosecond laser pulse on a nanoparticle, including the absorption of photons. Understanding the sequence of events after photon absorption and their timescales is important for many applications of nanoparticles. Various processes are discussed, starting with optical absorption by electrons, proceeding through the relaxation of the electrons due to electron–electron scattering and electron–phonon coupling, and ending with the dissipation of the nanoparticle energy into the environment. The goal is to consider the timescales, values, and temperature dependences of the electron heat capacity and the electron–phonon coupling parameter that describe these processes and how these dependences affect the electron energy relaxation. Two- and four-temperature models for describing electron–phonon relaxation are discussed. Significant emphasis is paid to the proposed analytical approach to modeling processes during the action of a femtosecond laser pulse on a metal nanoparticle. These consider the temperature dependences of the electron heat capacity and the electron–phonon coupling factor of the metal. The entire process is divided into four stages: (1) the heating of the electron system by a pulse, (2) electron thermalization, (3) electron–phonon energy exchange and the equalization of the temperature of the electrons with the lattice, and (4) cooling of the nanoparticle. There is an appropriate analytical description of each stage. The four-temperature model can estimate the parameters of the laser and nanoparticles needed for applications of femtosecond laser pulses and nanoparticles.
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Affiliation(s)
- Victor K. Pustovalov
- Belarussian National Technical University, Pr. Independency, 65, Minsk 220013, Belarus
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4
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Zahn D, Seiler H, Windsor YW, Ernstorfer R. Ultrafast lattice dynamics and electron-phonon coupling in platinum extracted with a global fitting approach for time-resolved polycrystalline diffraction data. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:064301. [PMID: 34805449 PMCID: PMC8594951 DOI: 10.1063/4.0000120] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 10/18/2021] [Indexed: 05/05/2023]
Abstract
Quantitative knowledge of electron-phonon coupling is important for many applications as well as for the fundamental understanding of nonequilibrium relaxation processes. Time-resolved diffraction provides direct access to this knowledge through its sensitivity to laser-induced lattice dynamics. Here, we present an approach for analyzing time-resolved polycrystalline diffraction data. A two-step routine is used to minimize the number of time-dependent fit parameters. The lattice dynamics are extracted by finding the best fit to the full transient diffraction pattern rather than by analyzing transient changes of individual Debye-Scherrer rings. We apply this approach to platinum, an important component of novel photocatalytic and spintronic applications, for which a large variation of literature values exists for the electron-phonon coupling parameterG ep . Based on the extracted evolution of the atomic mean squared displacement and using a two-temperature model, we obtainG ep = ( 3.9 ± 0.2 ) × 10 17 W m 3 K (statistical error). We find that at least up to an absorbed energy density of 124 J/cm3,G ep is not fluence-dependent. Our results for the lattice dynamics of platinum provide insights into electron-phonon coupling and phonon thermalization and constitute a basis for quantitative descriptions of platinum-based heterostructures in nonequilibrium conditions.
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Affiliation(s)
- Daniela Zahn
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Hélène Seiler
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
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5
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Kang K, Choi GM. Electron-Phonon Coupling Parameter of Ferromagnetic Metal Fe and Co. MATERIALS (BASEL, SWITZERLAND) 2021; 14:2755. [PMID: 34071011 PMCID: PMC8197080 DOI: 10.3390/ma14112755] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/19/2021] [Accepted: 05/21/2021] [Indexed: 11/22/2022]
Abstract
The electron-phonon coupling (g) parameter plays a critical role in the ultrafast transport of heat, charge, and spin in metallic materials. However, the exact determination of the g parameter is challenging because of the complicated process during the non-equilibrium state. In this study, we investigate the g parameters of ferromagnetic 3d transition metal (FM) layers, Fe and Co, using time-domain thermoreflectance. We measure a transient increase in temperature of Au in an FM/Au bilayer; the Au layer efficiently detects the strong heat flow during the non-equilibrium between electrons and phonons in FM. The g parameter of the FM is determined by analyzing the temperature dynamics using thermal circuit modeling. The determined g values are 8.8-9.4 × 1017 W m-3 K-1 for Fe and 9.6-12.2 × 1017 W m-3 K-1 for Co. Our results demonstrate that all 3d transition FMs have a similar g value, in the order of 1018 W m-3 K-1.
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Affiliation(s)
- Kyuhwe Kang
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Korea;
| | - Gyung-Min Choi
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Korea;
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Korea
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Bach N, Schäfer S. Ultrafast strain propagation and acoustic resonances in nanoscale bilayer systems. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:035101. [PMID: 34169119 PMCID: PMC8214470 DOI: 10.1063/4.0000079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 04/21/2021] [Indexed: 06/13/2023]
Abstract
Ultrafast structural probing has greatly enhanced our understanding of the coupling of atomic motion to electronic and phononic degrees-of-freedom in quasi-bulk materials. In bi- and multilayer model systems, additionally, spatially inhomogeneous relaxation channels are accessible, often governed by pronounced interfacial couplings and local excitations in confined geometries. Here, we systematically explore the key dependencies of the low-frequency acoustic phonon spectrum in an elastically mismatched metal/semiconductor bilayer system optically excited by femtosecond laser pulses. We track the spatiotemporal strain wave propagation in the heterostructure employing a discrete numerical linear chain simulation and access acoustic wave reflections and interfacial couplings with a phonon mode description based on a continuum mechanics model. Due to the interplay of elastic properties and mass densities of the two materials, acoustic resonance frequencies of the heterostructure significantly differ from breathing modes in monolayer films. For large acoustic mismatch, the spatial localization of phonon eigenmodes is derived from analytical approximations and can be interpreted as harmonic oscillations in decoupled mechanical resonators.
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Affiliation(s)
- N. Bach
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
| | - S. Schäfer
- Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany
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7
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Jaiswal J, Mourya S, Malik G, Chauhan S, Sanger A, Daipuriya R, Singh M, Chandra R. Determination of optical constants including surface characteristics of optically thick nanostructured Ti films: analyzed by spectroscopic ellipsometry. APPLIED OPTICS 2016; 55:8368-8375. [PMID: 27828089 DOI: 10.1364/ao.55.008368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In the present work, optically thick nanostructured titanium (Ti) films of thickness ranging from ∼100 to 900 nm were deposited on a glass substrate by DC magnetron sputtering at room temperature. Microstructural and surface properties of the samples were studied by x-ray diffraction and x-ray photoelectron spectroscopy (XPS). The morphological results revealed a systematic normal grain growth mechanism with increasing thickness analyzed by a scanning electron microscope. The influence of thickness on film surface roughness has been investigated by atomic force microscopy (AFM). The optical dispersion behavior was examined by spectroscopic ellipsometry (SE) over the long wavelength range of 246-1688 nm. The experimentally observed SE parameters were theoretically fitted with Drude-Lorentz and Bruggeman effective medium approximation theory. The surface properties of the Ti film measured by XPS and AFM were further accounted for in the optical model to determine optical constants (n and k) and the obtained results are expected to be the best available for bulk Ti metal.
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Samolyuk GD, Béland LK, Stocks GM, Stoller RE. Electron-phonon coupling in Ni-based binary alloys with application to displacement cascade modeling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:175501. [PMID: 27033732 DOI: 10.1088/0953-8984/28/17/175501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Energy transfer between lattice atoms and electrons is an important channel of energy dissipation during displacement cascade evolution in irradiated materials. On the assumption of small atomic displacements, the intensity of this transfer is controlled by the strength of electron-phonon (el-ph) coupling. The el-ph coupling in concentrated Ni-based alloys was calculated using electronic structure results obtained within the coherent potential approximation. It was found that Ni0.5Fe0.5, Ni0.5Co0.5 and Ni0.5Pd0.5 are ordered ferromagnetically, whereas Ni0.5Cr0.5 is nonmagnetic. Since the magnetism in these alloys has a Stoner-type origin, the magnetic ordering is accompanied by a decrease of electronic density of states at the Fermi level, which in turn reduces the el-ph coupling. Thus, the el-ph coupling values for all alloys are approximately 50% smaller in the magnetic state than for the same alloy in a nonmagnetic state. As the temperature increases, the calculated coupling initially increases. After passing the Curie temperature, the coupling decreases. The rate of decrease is controlled by the shape of the density of states above the Fermi level. Introducing a two-temperature model based on these parameters in 10 keV molecular dynamics cascade simulation increases defect production by 10-20% in the alloys under consideration.
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Affiliation(s)
- G D Samolyuk
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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9
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Guillemet T, Kusiak A, Fan L, Heintz JM, Chandra N, Zhou Y, Silvain JF, Lu Y, Battaglia JL. Thermal characterization of diamond films through modulated photothermal radiometry. ACS APPLIED MATERIALS & INTERFACES 2014; 6:2095-2102. [PMID: 24422442 DOI: 10.1021/am405188r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Diamond (Dia) films are promising heat-dissipative materials for electronic packages because they combine high thermal conductivity with high electrical resistivity. However, precise knowledge of the thermal properties of the diamond films is crucial to their potential application as passive thermal management substrates in electronics. In this study, modulated photothermal radiometry in a front-face configuration was employed to thermally characterize polycrystalline diamond films deposited onto silicon (Si) substrates through laser-assisted combustion synthesis. The intrinsic thermal conductivity of diamond films and the thermal boundary resistance at the interface between the diamond film and the Si substrate were investigated. The results enlighten the correlation between the deposition process, film purity, film transverse thermal conductivity, and interface thermal resistance.
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Affiliation(s)
- Thomas Guillemet
- Institut de Chimie de la Matière Condensée de Bordeaux, CNRS, Université de Bordeaux , 33608 Pessac, France
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10
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Resolving the role of femtosecond heated electrons in ultrafast spin dynamics. Sci Rep 2014; 4:3980. [PMID: 24496221 PMCID: PMC3913971 DOI: 10.1038/srep03980] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Accepted: 01/15/2014] [Indexed: 11/08/2022] Open
Abstract
Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal.
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11
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Thermal Transport across Solid Interfaces with Nanoscale Imperfections: Effects of Roughness, Disorder, Dislocations, and Bonding on Thermal Boundary Conductance. ACTA ACUST UNITED AC 2013. [DOI: 10.1155/2013/682586] [Citation(s) in RCA: 194] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The efficiency in modern technologies and green energy solutions has boiled down to a thermal engineering problem on the nanoscale. Due to the magnitudes of the thermal mean free paths approaching or overpassing typical length scales in nanomaterials (i.e., materials with length scales less than one micrometer), the thermal transport across interfaces can dictate the overall thermal resistance in nanosystems. However, the fundamental mechanisms driving these electron and phonon interactions at nanoscale interfaces are difficult to predict and control since the thermal boundary conductance across interfaces is intimately related to the characteristics of the interface (structure, bonding, geometry, etc.) in addition to the fundamental atomistic properties of the materials comprising the interface itself. In this paper, I review the recent experimental progress in understanding the interplay between interfacial properties on the atomic scale and thermal transport across solid interfaces. I focus this discussion specifically on the role of interfacial nanoscale “imperfections,” such as surface roughness, compositional disorder, atomic dislocations, or interfacial bonding. Each type of interfacial imperfection leads to different scattering mechanisms that can be used to control the thermal boundary conductance. This offers a unique avenue for controlling scattering and thermal transport in nanotechnology.
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12
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Sayer RA, Piekos ES, Phinney LM. Modified data analysis for thermal conductivity measurements of polycrystalline silicon microbridges using a steady state Joule heating technique. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:124904. [PMID: 23278015 DOI: 10.1063/1.4769059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Accurate knowledge of thermophysical properties is needed to predict and optimize the thermal performance of microsystems. Thermal conductivity is experimentally determined by measuring quantities such as voltage or temperature and then inferring a thermal conductivity from a thermal model. Thermal models used for data analysis contain inherent assumptions, and the resultant thermal conductivity value is sensitive to how well the actual experimental conditions match the model assumptions. In this paper, a modified data analysis procedure for the steady state Joule heating technique is presented that accounts for bond pad effects including thermal resistance, electrical resistance, and Joule heating. This new data analysis method is used to determine the thermal conductivity of polycrystalline silicon (polysilicon) microbridges fabricated using the Sandia National Laboratories SUMMiT V™ micromachining process over the temperature range of 77-350 K, with the value at 300 K being 71.7 ± 1.5 W/(m K). It is shown that making measurements on beams of multiple lengths is useful, if not essential, for inferring the correct thermal conductivity from steady state Joule heating measurements.
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Affiliation(s)
- Robert A Sayer
- Engineering Sciences Center, Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA
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13
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Hopkins PE, Klopf JM, Norris PM. Influence of interband transitions on electron-phonon coupling measurements in Ni films. APPLIED OPTICS 2007; 46:2076-83. [PMID: 17384723 DOI: 10.1364/ao.46.002076] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The reduction in size and the increase in speed of opto- and magnetoelectronic devices is making the probability of nonequilibrium electron-phonon phenomena greater, leading to increased thermal resistance in these devices. The measurement of electron-phonon coupling in materials in these devices is becoming increasingly important for accurate thermal management. Here femtosecond thermoreflectance is used to measure the electron-phonon coupling factor in thin Ni films of varying thickness grown on Si and glass substrates. The thermoreflectance response is measured at 1.3 and 1.55 eV, yielding drastically different responses due to the Fermi-level transition at 1.3 eV in Ni. The influence of this transition on the thermoreflectance response results in a measurement of the electron-phonon coupling factor that is twice as high as that recorded in previous measurements that were unaffected by the Fermi-level transition.
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Affiliation(s)
- Patrick E Hopkins
- Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22904-4746, USA
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