Three-Dimensional Orientation Mapping in the Transmission Electron Microscope

Liu, Haihua; Schmidt, Søren; Poulsen, Henning Friis; Godfrey, A.; Liu, Z.Q.; Sharon, John Anthony; Huang, Xiaoxu

doi:10.1126/science.1202202

Cited by 116 publications

(80 citation statements)

References 12 publications

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“…This nanodiffraction-based technique has a spatial resolution of ∼1 nm that is comparable to the conical-scanning dark-field imaging approach 19 . In a standard IPFOM image, 250,000 frames of diffraction patterns were collected, each of which was indexed by EDAX orientation-image-mapping indexing software and applied to determine the crystallographic orientations.…”

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confidence: 97%

Defective twin boundaries in nanotwinned metals

et al. 2013

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Coherent twin boundaries (CTBs) are widely described, both theoretically and experimentally, as perfect interfaces that play a significant role in a variety of materials. Although the ability of CTBs in strengthening, maintaining the ductility and minimizing the electron scattering is well documented [1][2][3] , most of our understanding of the origin of these properties relies on perfect-interface assumptions. Here we report experiments and simulations demonstrating that as-grown CTBs in nanotwinned copper are inherently defective with kink-like steps and curvature, and that these imperfections consist of incoherent segments and partial dislocations. We further show that these defects play a crucial role in the deformation mechanisms and mechanical behaviour of nanotwinned copper. Our findings offer a view of the structure of CTBs that is largely different from that in the literature 2,4,5 , and underscore the significance of imperfections in nanotwinstrengthened materials.CTBs formed during growth, deformation or annealing exist broadly in many crystalline solids with low or medium stackingfault energies 1,5,6 . The strengthening behaviour and other attractive properties of CTBs have been studied in nanotwinned metals (with an average twin spacing <100 nm; refs 7-9). One prevalent view is that CTB-strengthened materials have certain advantages over nanocrystalline or ultrafine-grained materials; that is, materials strengthened through traditional grain boundaries (GBs) that are considered incoherent and defective 10 . GBs not only scatter electrons, but can migrate and slide under shear stresses 11 , leading to a maximum in strength in nanocrystalline materials 12,13 . In contrast, such migration/sliding mechanisms may not be operative in CTBs despite some reports of detwinning evidence 7,14,15 and the observation of a similar maximum strength in a nanotwinned copper 3 (nt-Cu). Existing models widely assume perfect CTBs and rationalize flow softening due to CTB migrations and detwinning as caused by nucleation and motion of partial dislocations parallel to CTBs (ref. 4). These mechanisms are informative as long as CTB lengths are limited to the tens of nanometres typically used in molecular dynamics simulations 4,[16][17][18] . It still remains difficult through molecular dynamics simulations to validate the migrations/detwinning of the much longer CTBs seen in experiments (500 nm; ref. 3). There could be alternative mechanisms that are intricately related to the potential structures of CTBs and the characteristics of GBs, both of which are not accounted for in the literature.Recent studies of nanotwinned copper pillars without GBs revealed strong deformation anisotropy and a brittle-to-ductile transition behaviour (where CTBs are considered intrinsically brittle) 2 , suggesting that CTBs alone are not sufficient for increased plasticity despite their strong strengthening effect, and that a reasonable mix of GBs is helpful to mediate the plasticity and achieve high ductility. Experiments and simulations have f...

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confidence: 97%

Defective twin boundaries in nanotwinned metals

et al. 2013

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“…Subsequently, we colorized and merged the dark field images to map crystallite orientation within the nanoparticle aggregates (see Supplementary Information for a full description of methods and additional data). By distinguishing overlapping crystals, this new DF-TEM technique provides some of the information content achieved by three-dimensional DF-TEM 27 while retaining the simplicity of traditional two-dimensional DF-TEM 28,29 .…”

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confidence: 99%

“…This allows meaningful information to be extracted from materials with high structural complexity. It is likely that even further insight will be gained by extending the analysis using three dimensional orientational imaging 27 , although the relative simplicity of the DF-TEM technique developed here is compelling. Our studies suggest that there are champion nanoparticle aggregates that are largely responsible for the high photocurrent in the present samples.…”

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confidence: 99%

Identifying champion nanostructures for solar water-splitting

et al. 2013

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Citation for published item:rrenD FgF nd o¤ %t hovskyD uF nd hot nD rF nd veroyD gFwF nd gornuzD wF nd tell iD pF nd r¡ e ertD gF nd oths hildD eF nd qr¤ tzelD wF @PHIQA 9sdentifying h mpion n nostru tures for sol r w terEsplittingF9D x ture m teri lsFD IP @WAF ppF VRPEVRWF Further information on publisher's website: httpXGGdxFdoiForgGIHFIHQVGnm tQTVR Publisher's copyright statement: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Charge transport in nanoparticle-based materials underlies many emerging energy conversion technologies, yet assessing the impact of nanometer-scale structure on charge transport across micron-scale distances remains a challenge. Here we develop an approach for correlating the spatial distribution of crystalline and current-carrying domains in entire nanoparticle aggregates. We apply this approach to nanoparticle-based α-Fe 2 O 3 electrodes that are of interest in solar-to-hydrogen energy conversion. In correlating structure and charge transport with nanometer resolution across micron-scale distances, we have identified the existence of champion nanoparticle aggregates that are most responsible for the high photoelectrochemical activity of the present electrodes. Indeed, when electrodes are fabricated with a high proportion of these champion nanostructures, the electrodes achieve the highest photocurrent of any metal oxide photoanode for photoelectrochemical water splitting under 100 mW cm -2 air mass 1.5 global sunlight.Batteries, fuel cells, and solar energy conversion devices have emerged as a class of important technologies that increasingly rely upon electrodes derived from nanoparticles 1 . These nanoparticle-based materials provide a unique challenge in assessing structure-property relationships because of the disordered arrangement of nanocrystals that results when nanoparticles collide and aggregate [2][3][4][5][6] . The morphological evolution that follows aggregation further obscures the influence of particle size, shape, and interfacial characteristics in defining the physical properties of these materials 7,8 . For the nanoparticle-based electrodes used in solar energy conversion, structural defects such as grain boundaries define pathways for charge transport by creating potential barriers and by promoting recombination 9 . Because of the complexity of these materials, within a single electrode there may exist a small proportion of "champion" nanostructures-by analogy with champion solar cells 10,11 , these are nanostructures that provide the highest solar conversion efficiencies-th...

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“…41 The exact nature of these local effects is unknown; however, interaction of ferroic domains at grain boundaries and the coupling of extrinsic ferroelectric/ferroelastic strains with the elastic anisotropy of the system are suspected to have an influence. Further development of grain-scale microscopy methods based on 3DXRD, 42,43 diffraction contrast tomography, [44][45][46] darkfield X-rays, 47,48 or transmitted electrons 49 will allow the possibility to establish three-dimensional grain neighbour relations experimentally, quantify intergranular interactions (in particular, stresses and strains, both intrinsic and extrinsic), and build these into predictive models. [50][51][52] Development of these characterisation techniques and predictive modelling covering multiple length scales may be the key tools needed in order to design new reversible phase-change actuator ceramics with improved fatigue properties compared to present generation ceramics.…”

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confidence: 99%

Maximising electro-mechanical response by minimising grain-scale strain heterogeneity in phase-change actuator ceramics

Oddershede¹,

Hossain

Daniels

2016

Applied Physics Letters

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Phase-change actuator ceramics directly couple electrical and mechanical energies through an electric-field-induced phase transformation. These materials are promising for the replacement of the most common electro-mechanical ceramic, lead zirconate titanate, which has environmental concerns. Here, we show that by compositional modification, we reduce the grain-scale heterogeneity of the electro-mechanical response by 40%. In the materials investigated, this leads to an increase in the achievable electric-field-induced strain of the bulk ceramic of 45%. Compositions of (100–x)Bi0.5Na0.5TiO3–(x)BaTiO3, which initially possess a pseudo-cubic symmetry, can be tuned to undergo phase transformations to combined lower symmetry phases, thus decreasing the anisotropy of the transformation strain. Further, modelling of transformation strains of individual grains shows that minimum grain-scale strain heterogeneity can be achieved by precise control of the lattice distortions and orientation distributions of the induced phases. The current results can be used to guide the design of next generation high-strain electro-mechanical ceramic actuator materials.

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Three-Dimensional Orientation Mapping in the Transmission Electron Microscope

Cited by 116 publications

References 12 publications

Defective twin boundaries in nanotwinned metals

Defective twin boundaries in nanotwinned metals

Identifying champion nanostructures for solar water-splitting

Maximising electro-mechanical response by minimising grain-scale strain heterogeneity in phase-change actuator ceramics

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