1
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Siddiqui KM, Durham DB, Cropp F, Ji F, Paiagua S, Ophus C, Andresen NC, Jin L, Wu J, Wang S, Zhang X, You W, Murnane M, Centurion M, Wang X, Slaughter DS, Kaindl RA, Musumeci P, Minor AM, Filippetto D. Relativistic ultrafast electron diffraction at high repetition rates. Struct Dyn 2023; 10:064302. [PMID: 38058995 PMCID: PMC10697722 DOI: 10.1063/4.0000203] [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] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 11/08/2023] [Indexed: 12/08/2023]
Abstract
The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials science. The last couple of decades have witnessed ultrafast electron diffraction (UED) emerge as one of the forefront techniques with the sensitivity to resolve atomic motions. Increasingly sophisticated UED instruments are being developed that are aimed at increasing the beam brightness in order to observe structural signatures, but so far they have been limited to low average current beams. Here, we present the technical design and capabilities of the HiRES (High Repetition-rate Electron Scattering) instrument, which blends relativistic electrons and high repetition rates to achieve orders of magnitude improvement in average beam current compared to the existing state-of-the-art instruments. The setup utilizes a novel electron source to deliver femtosecond duration electron pulses at up to MHz repetition rates for UED experiments. Instrument response function of sub-500 fs is demonstrated with < 100 fs time resolution targeted in future. We provide example cases of diffraction measurements on solid-state and gas-phase samples, including both micro- and nanodiffraction (featuring 100 nm beam size) modes, which showcase the potential of the instrument for novel UED experiments.
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Affiliation(s)
- K. M. Siddiqui
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | | | | | - F. Ji
- Accelerator Technology and Applied Physics Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - S. Paiagua
- Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, USA
| | - C. Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - N. C. Andresen
- Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - L. Jin
- Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - J. Wu
- Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - S. Wang
- Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, USA
| | - X. Zhang
- Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - W. You
- Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, USA
| | - M. Murnane
- Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, USA
| | - M. Centurion
- Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - X. Wang
- Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - D. S. Slaughter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California 94720, USA
| | | | - P. Musumeci
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | | | - D. Filippetto
- Accelerator Technology and Applied Physics Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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2
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Terzoudis-Lumsden EWC, Petersen TC, Brown HG, Pelz PM, Ophus C, Findlay SD. Resolution of Virtual Depth Sectioning from Four-Dimensional Scanning Transmission Electron Microscopy. Microsc Microanal 2023; 29:1409-1421. [PMID: 37488824 DOI: 10.1093/micmic/ozad068] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 03/15/2023] [Accepted: 05/25/2023] [Indexed: 07/26/2023]
Abstract
One approach to three-dimensional structure determination using the wealth of scattering data in four-dimensional (4D) scanning transmission electron microscopy (STEM) is the parallax method proposed by Ophus et al. (2019. Advanced phase reconstruction methods enabled by 4D scanning transmission electron microscopy, Microsc Microanal25, 10-11), which determines the scattering matrix and uses it to synthesize a virtual depth-sectioning reconstruction of the sample structure. Drawing on an equivalence with a hypothetical confocal imaging mode, we derive contrast transfer and point spread functions for this parallax method applied to weakly scattering objects, showing them identical to earlier depth-sectioning STEM modes when only bright field signal is used, but that improved depth resolution is possible if dark field signal can be used. Through a simulation-based study of doped Si, we show that this depth resolution is preserved for thicker samples, explore the impact of shot noise on the parallax reconstructions, discuss challenges to making use of dark field signal, and identify cases where the interpretation of the parallax reconstruction breaks down.
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Affiliation(s)
| | - T C Petersen
- School of Physics and Astronomy, Monash University, Melbourne, VIC 3800, Australia
- Monash Centre for Electron Microscopy, Monash University, Melbourne, VIC 3800, Australia
| | - H G Brown
- Ian Holmes Imaging Center, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC 3052, Australia
| | - P M Pelz
- Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Bavaria 91058, Germany
| | - C Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - S D Findlay
- School of Physics and Astronomy, Monash University, Melbourne, VIC 3800, Australia
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3
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Schweizer P, Vogl L, Spiecker E, Ophus C, Minor A. Structure and Dynamics of Graphite Intercalation Compounds Analyzed using in situ 4D-STEM. Microsc Microanal 2023; 29:1279-1280. [PMID: 37613685 DOI: 10.1093/micmic/ozad067.654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- P Schweizer
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - L Vogl
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - E Spiecker
- Institute for Micro- and Nanoanalysis, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - C Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - A Minor
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
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4
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Yang M, Li Q, Chopdekar RV, Dhall R, Turner J, Carlström JD, Ophus C, Klewe C, Shafer P, N'Diaye AT, Choi JW, Chen G, Wu YZ, Hwang C, Wang F, Qiu ZQ. Creation of skyrmions in van der Waals ferromagnet Fe 3GeTe 2 on (Co/Pd) n superlattice. Sci Adv 2020; 6:6/36/eabb5157. [PMID: 32917619 PMCID: PMC7473669 DOI: 10.1126/sciadv.abb5157] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 07/15/2020] [Indexed: 05/27/2023]
Abstract
Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe3GeTe2 on top of (Co/Pd) n in which the Fe3GeTe2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe3GeTe2 and the (Co/Pd) n could create skyrmions in Fe3GeTe2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.
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Affiliation(s)
- M Yang
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Q Li
- Department of Physics, University of California, Berkeley, CA 94720, USA.
| | - R V Chopdekar
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - R Dhall
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J Turner
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J D Carlström
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - C Ophus
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - C Klewe
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - P Shafer
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - A T N'Diaye
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J W Choi
- Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
| | - G Chen
- Department of Physics, University of California, Davis, CA 95616, USA
| | - Y Z Wu
- Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
| | - C Hwang
- Korea Research Institute of Standards and Science, Yuseong, Daejeon 305-340, Republic of Korea
| | - F Wang
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Z Q Qiu
- Department of Physics, University of California, Berkeley, CA 94720, USA.
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5
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Brown HG, Chen Z, Weyland M, Ophus C, Ciston J, Allen LJ, Findlay SD. Structure Retrieval at Atomic Resolution in the Presence of Multiple Scattering of the Electron Probe. Phys Rev Lett 2018; 121:266102. [PMID: 30636159 DOI: 10.1103/physrevlett.121.266102] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 11/04/2018] [Indexed: 06/09/2023]
Abstract
The projected electrostatic potential of a thick crystal is reconstructed at atomic resolution from experimental scanning transmission electron microscopy data recorded using a new generation fast-readout electron camera. This practical and deterministic inversion of the equations encapsulating multiple scattering that were written down by Bethe in 1928 removes the restriction of established methods to ultrathin (≲50 Å) samples. Instruments already coming on line can overcome the remaining resolution-limiting effects in this method due to finite probe-forming aperture size, spatial incoherence, and residual lens aberrations.
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Affiliation(s)
- H G Brown
- School of Physics and Astronomy, Monash University, Victoria 3800, Australia
| | - Z Chen
- School of Physics and Astronomy, Monash University, Victoria 3800, Australia
| | - M Weyland
- Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria 3800, Australia
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia
| | - C Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - J Ciston
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - L J Allen
- School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - S D Findlay
- School of Physics and Astronomy, Monash University, Victoria 3800, Australia
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6
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Schwartz O, Axelrod JJ, Tuthill DR, Haslinger P, Ophus C, Glaeser RM, Müller H. Near-concentric Fabry-Pérot cavity for continuous-wave laser control of electron waves. Opt Express 2017; 25:14453-14462. [PMID: 28789031 DOI: 10.1364/oe.25.014453] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Accepted: 06/02/2017] [Indexed: 06/07/2023]
Abstract
Manipulating free-space electron wave functions with laser fields can bring about new electron-optical elements for transmission electron microscopy (TEM). In particular, a Zernike phase plate would enable high-contrast TEM imaging of soft matter, leading to new opportunities in structural biology and materials science. A Zernike phase plate can be implemented using a tight, intense continuous laser focus that shifts the phase of the electron wave by the ponderomotive potential. Here, we use a near-concentric cavity to focus 7.5 kW of continuous-wave circulating laser power at 1064 nm into a 7 µm mode waist, achieving a record continuous laser intensity of 40 GW/cm2. Such parameters are sufficient to impart a phase shift of 1 rad to a 10 keV electron beam, or 0.16 rad to a 300 keV beam. Our numerical simulations confirm that the standing-wave phase shift profile imprinted on the electron wave by the intra-cavity field can serve as a nearly ideal Zernike phase plate.
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7
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Bowers ML, Ophus C, Gautam A, Lançon F, Dahmen U. Step Coalescence by Collective Motion at an Incommensurate Grain Boundary. Phys Rev Lett 2016; 116:106102. [PMID: 27015493 DOI: 10.1103/physrevlett.116.106102] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 06/05/2023]
Abstract
Using extended time series scanning transmission electron microscopy, we investigate structural fluctuations at an incommensurate grain boundary in Au. Atomic-resolution imaging reveals the coalescence of two interfacial steps, or disconnections, of different height via coordinated motion of atoms along close-packed directions. Numerical simulations uncover a transition pathway that involves constriction and expansion of a characteristic stacking fault often associated with grain boundaries in face-centered cubic materials. It is found that local atomic fluctuations by enhanced point defect diffusion may play a critical role in initiating this transition. Our results offer new insights into the collective motion of atoms underlying the lateral advance of steps that control the migration of faceted grain boundaries.
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Affiliation(s)
- M L Bowers
- Molecular Foundry, National Center for Electron Microscopy, LBNL, Berkeley, California 94720, USA
| | - C Ophus
- Molecular Foundry, National Center for Electron Microscopy, LBNL, Berkeley, California 94720, USA
| | - A Gautam
- Molecular Foundry, National Center for Electron Microscopy, LBNL, Berkeley, California 94720, USA
| | - F Lançon
- Université Grenoble Alpes, 38042 Grenoble, France, and INAC, SP2M, L_sim, CEA, 38054 Grenoble, France
| | - U Dahmen
- Molecular Foundry, National Center for Electron Microscopy, LBNL, Berkeley, California 94720, USA
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8
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Ciston J, Brown HG, D'Alfonso AJ, Koirala P, Ophus C, Lin Y, Suzuki Y, Inada H, Zhu Y, Allen LJ, Marks LD. Surface determination through atomically resolved secondary-electron imaging. Nat Commun 2015; 6:7358. [PMID: 26082275 PMCID: PMC4557350 DOI: 10.1038/ncomms8358] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 04/29/2015] [Indexed: 11/30/2022] Open
Abstract
Unique determination of the atomic structure of technologically relevant surfaces is often limited by both a need for homogeneous crystals and ambiguity of registration between the surface and bulk. Atomically resolved secondary-electron imaging is extremely sensitive to this registration and is compatible with faceted nanomaterials, but has not been previously utilized for surface structure determination. Here we report a detailed experimental atomic-resolution secondary-electron microscopy analysis of the c(6 × 2) reconstruction on strontium titanate (001) coupled with careful simulation of secondary-electron images, density functional theory calculations and surface monolayer-sensitive aberration-corrected plan-view high-resolution transmission electron microscopy. Our work reveals several unexpected findings, including an amended registry of the surface on the bulk and strontium atoms with unusual seven-fold coordination within a typically high surface coverage of square pyramidal TiO5 units. Dielectric screening is found to play a critical role in attenuating secondary-electron generation processes from valence orbitals.
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Affiliation(s)
- J. Ciston
- National Center for Electron Microscopy, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - H. G. Brown
- School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - A. J. D'Alfonso
- School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - P. Koirala
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - C. Ophus
- National Center for Electron Microscopy, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Y. Lin
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Y. Suzuki
- Application Development Department, Hitachi High Technologies Corp., Ibaraki 312-8504, Japan
| | - H. Inada
- Advanced Microscope Design Department, Hitachi High Technologies Corp., Ibaraki 312-8504, Japan
| | - Y. Zhu
- Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - L. J. Allen
- School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - L. D. Marks
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
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9
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Gautam A, Ophus C, Lançon F, Denes P, Dahmen U. Analysis of grain boundary dynamics using event detection and cumulative averaging. Ultramicroscopy 2014; 151:78-84. [PMID: 25498139 DOI: 10.1016/j.ultramic.2014.11.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 11/06/2014] [Accepted: 11/06/2014] [Indexed: 11/28/2022]
Abstract
To analyze extended time series of high resolution images, we have employed automated frame-by-frame comparisons that are able to detect dynamic changes in the structure of a grain boundary in Au. Using cumulative averaging of images between events allowed high resolution measurements of the atomic relaxation in the interface with sufficient accuracy for comparison with atomistic models. Cumulative averaging was also used to observe the structural rearrangement of atomic columns at a moving step in the grain boundary. The technique of analyzing changing features in high resolution images by averaging between incidents can be used to deconvolute stochastic events that occur at random intervals and on time scales well beyond that accessible to single-shot imaging.
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Affiliation(s)
- A Gautam
- National Center for Electron Microscopy, LBNL, Berkeley, CA 94720, USA
| | - C Ophus
- National Center for Electron Microscopy, LBNL, Berkeley, CA 94720, USA
| | - F Lançon
- Laboratoire de Simulation Atomistique (L_Sim), SP2M, INAC, CEA, 38054 Grenoble, France
| | - P Denes
- National Center for Electron Microscopy, LBNL, Berkeley, CA 94720, USA
| | - U Dahmen
- National Center for Electron Microscopy, LBNL, Berkeley, CA 94720, USA.
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10
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Radmilovic V, Ophus C, Marquis EA, Rossell MD, Tolley A, Gautam A, Asta M, Dahmen U. Highly monodisperse core-shell particles created by solid-state reactions. Nat Mater 2011; 10:710-715. [PMID: 21822262 DOI: 10.1038/nmat3077] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
The size distribution of particles, which is essential for many properties of nanomaterials, is equally important for the mechanical behaviour of the class of alloys whose strength derives from a dispersion of nanoscale precipitates. However, particle size distributions formed by solid-state precipitation are generally not well controlled. Here we demonstrate, through the example of core-shell precipitates in Al-Sc-Li alloys, an approach to forming highly monodisperse particle size distributions by simple solid-state reactions. The approach involves the use of a two-step heat treatment, whereby the core formed at high temperature provides a template for growth of the shell at lower temperature. If the core is allowed to grow to a sufficient size, the shell develops in a 'size focusing' regime, where smaller particles grow faster than larger ones. These results suggest strategies for manipulating precipitate size distributions in similar systems through simple variations in thermal treatments.
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Affiliation(s)
- V Radmilovic
- National Center for Electron Microscopy, Materials Science Division, Lawrence Berkeley National Lab, Berkeley, California 94720, USA.
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11
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Luber EJ, Olsen BC, Ophus C, Radmilovic V, Mitlin D. All-metal AFM probes fabricated from microstructurally tailored Cu-Hf thin films. Nanotechnology 2009; 20:345703. [PMID: 19652276 DOI: 10.1088/0957-4484/20/34/345703] [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: 05/28/2023]
Abstract
A growing number of atomic force microscope (AFM) applications make use of metal-coated probes. Probe metallization can cause adverse side-effects and disadvantages such as stress-induced cantilever bending, thermal expansion mismatch, increased tip radius and limited device lifetime due to coating wear. In this study we demonstrate how to overcome these limitations using microstructural design to create a metallic glass thin film alloy, from which monostructural all-metal AFM cantilevers are fabricated. A detailed compositional study of co-sputtered Cu-Hf films is performed using x-ray diffraction (XRD), nanoindentation, four-point probe and in situ multi-beam optical stress sensing (MOSS). Metallic glass Cu(90)Hf(10) films are found to possess an optimal combination of electrical resistivity (96 microOmega cm), nanoindentation hardness (5.2 GPa), ductility and incremental stress. A continuum model is developed which uses measured MOSS data to predict cantilever warping caused by stress gradients generated during film growth. Subsequently, a microfabrication process is developed to create Cu(90)Hf(10) AFM probes. Uncurled, 1 microm thick cantilevers having lengths of 100-400 microm are fabricated, with tip radii ranging from 10 to 40 nm. As a proof of principle, these all-metal Cu-Hf AFM probes are mounted in a commercial AFM and used to successfully image a known test structure.
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Affiliation(s)
- E J Luber
- Chemical and Materials Engineering, University of Alberta, Canada.
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12
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Luber E, Mohammadi R, Ophus C, Lee Z, Nelson-Fitzpatrick N, Westra K, Evoy S, Dahmen U, Radmilovic V, Mitlin D. Tailoring the microstructure and surface morphology of metal thin films for nano-electro-mechanical systems applications. Nanotechnology 2008; 19:125705. [PMID: 21817746 DOI: 10.1088/0957-4484/19/12/125705] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Metallic structural components for micro-electro-mechanical/nano-electro-mechanical systems (MEMS/NEMS) are promising alternatives to silicon-based materials since they are electrically conductive, optically reflective and ductile. Polycrystalline mono-metallic films typically exhibit low strength and hardness, high surface roughness, and significant residual stress, making them unusable for NEMS. In this study we demonstrate how to overcome these limitations by co-sputtering Ni-Mo. Detailed investigation of the Ni-Mo system using transmission electron microscopy and high-resolution transmission electron microscopy (TEM/HRTEM), x-ray diffraction (XRD), nanoindentation, and atomic force microscopy (AFM) reveals the presence of an amorphous-nanocrystalline microstructure which exhibits enhanced hardness, metallic conductivity, and sub-nanometer root mean square (RMS) roughness. Uncurled NEMS cantilevers with MHz resonant frequencies and quality factors ranging from 200-900 are fabricated from amorphous Ni-Mo. Using a sub-regular solution model it is shown that the electrical conductivity of Ni-Mo is in excellent agreement with Bhatia's structural model of electrical resistivity in binary alloys. Using a Langevin-type stochastic rate equation the structural evolution of amorphous Ni-Mo is modeled; it is shown that the growth instability due to the competing processes of surface diffusion and self-shadowing is heavily damped out due to the high thermal energies of sputtering, resulting in extremely smooth films.
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Affiliation(s)
- E Luber
- Chemical and Materials Engineering, University of Alberta, Canada. National Institute of Nanotechnology, Edmonton, Canada
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