Showing papers on "Electron tomography published in 2013"

High-Resolution Electron Microscopy

Abstract: Preface Acknowledgements List of Symbols 1. Preliminaries 2. Electron Optics 3. Wave Optics 4. Coherence and Fourier Optics 5. High-Resolution Images of Crystals and their Defects 6. HREM in Biology, Organic Crystals and Radiation Damage 7. Image Processing and Superresolution Schemes 8. Stem and Z-Contrast 9. Electron Sources and Detectors 10. Measurement of Electron-optical Parameters Affecting High-Resolution Images 11. Instabilities and the Microscope Environment 12. Experimental Methods 13. Associated Techniques Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5

Three-dimensional imaging of dislocations in a nanoparticle at atomic resolution

Abstract: Dislocations and their interactions strongly influence many material properties, ranging from the strength of metals and alloys to the efficiency of light-emitting diodes and laser diodes. Several experimental methods can be used to visualize dislocations. Transmission electron microscopy (TEM) has long been used to image dislocations in materials, and high-resolution electron microscopy can reveal dislocation core structures in high detail, particularly in annular dark-field mode. A TEM image, however, represents a two-dimensional projection of a three-dimensional (3D) object (although stereo TEM provides limited information about 3D dislocations). X-ray topography can image dislocations in three dimensions, but with reduced resolution. Using weak-beam dark-field TEM and scanning TEM, electron tomography has been used to image 3D dislocations at a resolution of about five nanometres (refs 15, 16). Atom probe tomography can offer higher-resolution 3D characterization of dislocations, but requires needle-shaped samples and can detect only about 60 per cent of the atoms in a sample. Here we report 3D imaging of dislocations in materials at atomic resolution by electron tomography. By applying 3D Fourier filtering together with equal-slope tomographic reconstruction, we observe nearly all the atoms in a multiply twinned platinum nanoparticle. We observed atomic steps at 3D twin boundaries and imaged the 3D core structure of edge and screw dislocations at atomic resolution. These dislocations and the atomic steps at the twin boundaries, which appear to be stress-relief mechanisms, are not visible in conventional two-dimensional projections. The ability to image 3D disordered structures such as dislocations at atomic resolution is expected to find applications in materials science, nanoscience, solid-state physics and chemistry.

Cryo-electron tomography: The challenge of doing structural biology in situ

Abstract: Electron microscopy played a key role in establishing cell biology as a discipline, by producing fundamental insights into cellular organization and ultrastructure. Many seminal discoveries were made possible by the development of new sample preparation methods and imaging modalities. Recent technical advances include sample vitrification that faithfully preserves molecular structures, three-dimensional imaging by electron tomography, and improved image-processing methods. These new techniques have enabled the extraction of high fidelity structural information and are beginning to reveal the macromolecular organization of unperturbed cellular environments.

Hierarchical Porous Polymer Scaffolds from Block Copolymers

Abstract: Hierarchical porous polymer materials are of increasing importance because of their potential application in catalysis, separation technology, or bioengineering. Examples for their synthesis exist, but there is a need for a facile yet versatile conceptual approach to such hierarchical scaffolds and quantitative characterization of their nonperiodic pore systems. Here, we introduce a synthesis method combining well-established concepts of macroscale spinodal decomposition and nanoscale block copolymer self-assembly with porosity formation on both length scales via rinsing with protic solvents. We used scanning electron microscopy, small-angle x-ray scattering, transmission electron tomography, and nanoscale x-ray computed tomography for quantitative pore-structure characterization. The method was demonstrated for AB- and ABC-type block copolymers, and resulting materials were used as scaffolds for calcite crystal growth.

Orientation and phase mapping in the transmission electron microscope using precession-assisted diffraction spot recognition: state-of-the-art results

Abstract: A recently developed technique based on the transmission electron microscope, which makes use of electron beam precession together with spot diffraction pattern recognition now offers the possibility to acquire reliable orientation/phase maps with a spatial resolution down to 2 nm on a field emission gun transmission electron microscope. The technique may be described as precession-assisted crystal orientation mapping in the transmission electron microscope, precession-assisted crystal orientation mapping technique-transmission electron microscope, also known by its product name, ASTAR, and consists in scanning the precessed electron beam in nanoprobe mode over the specimen area, thus producing a collection of precession electron diffraction spot patterns, to be thereafter indexed automatically through template matching. We present a review on several application examples relative to the characterization of microstructure/microtexture of nanocrystalline metals, ceramics, nanoparticles, minerals and organics. The strengths and limitations of the technique are also discussed using several application examples.

Three-dimensional elemental mapping at the atomic scale in bimetallic nanocrystals.

Abstract: A thorough understanding of the three-dimensional (3D) atomic structure and composition of core-shell nanostructures is indispensable to obtain a deeper insight on their physical behavior. Such 3D information can be reconstructed from two-dimensional (2D) projection images using electron tomography. Recently, different electron tomography techniques have enabled the 3D characterization of a variety of nanostructures down to the atomic level. However, these methods have all focused on the investigation of nanomaterials containing only one type of chemical element. Here, we combine statistical parameter estimation theory with compressive sensing based tomography to determine the positions and atom type of each atom in heteronanostructures. The approach is applied here to investigate the interface in core-shell Au@Ag nanorods but it is of great interest in the investigation of a broad range of nanostructures.

Three-dimensional tomographic analyses of CeO2 nanoparticles

Abstract: A detailed morphological and structural analysis of CeO2 nanoparticles has been performed using electron tomography in scanning transmission mode in high angle annular dark field. The nanoparticles have been prepared through a solvothermal synthesis assisted by microwave heating. An adequate choice of the synthesis parameters leads to particles with various well-defined morphologies: cubes, octahedrons, and nanorods. In the case of cubic CeO2 nanoparticles, the three-dimensional analysis allowed us to precisely calculate the type and the proportion of the minor facets exposed at the nanoparticle surface. For the CeO2 nanoparticles with an octahedron shape, it has been demonstrated that the ambiguous interpretation of the objects giving triangular views in classical transmission electron microscopy can be prevented; furthermore, precise assignments of their external shape, surface crystallography, and type of minor facets were realized. In the case of nanorods, it was shown that the external shape and the ...

Nanometres-resolution Kikuchi patterns from materials science specimens with transmission electron forward scatter diffraction in the scanning electron microscope

Abstract: A charge-coupled device camera of an electron backscattered diffraction system in a scanning electron microscope was positioned below a thin specimen and transmission Kikuchi patterns were collected. Contrary to electron backscattered diffraction, transmission electron forward scatter diffraction provides phase identification and orientation mapping at the nanoscale. The minimum Pd particle size for which a Kikuchi diffraction pattern was detected and indexed reliably was 5.6 nm. An orientation mapping resolution of 5 nm was measured at 30 kV. The resolution obtained with transmission electron forward scatter diffraction was of the same order of magnitude than that reported in electron nanodiffraction in the transmission electron microscope. An energy dispersive spectrometer X-ray map and a transmission electron forward scatter diffraction orientation map were acquired simultaneously. The high-resolution chemical, phase and orientation maps provided at once information on the chemical form, orientation and coherency of precipitates in an aluminium-lithium 2099 alloy.

Sparse Imaging for Fast Electron Microscopy.

Abstract: Scanning electron microscopes (SEMs) are used in neuroscience and materials science to image centimeters of sample area at nanometer scales. Since imaging rates are in large part SNR-limited, large collections can lead to weeks of around-the-clock imaging time. To increase data collection speed, we propose and demonstrate on an operational SEM a fast method to sparsely sample and reconstruct smooth images. To accurately localize the electron probe position at fast scan rates, we model the dynamics of the scan coils, and use the model to rapidly and accurately visit a randomly selected subset of pixel locations. Images are reconstructed from the undersampled data by compressed sensing inversion using image smoothness as a prior. We report image fidelity as a function of acquisition speed by comparing traditional raster to sparse imaging modes. Our approach is equally applicable to other domains of nanometer microscopy in which the time to position a probe is a limiting factor (e.g., atomic force microscopy), or in which excessive electron doses might otherwise alter the sample being observed (e.g., scanning transmission electron microscopy).

Three-dimensional concentration mapping of organic blends

Abstract: We quantitatively measure the three-dimensional morphology of mixed organic layers using high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM) with electron tomography for the first time. The mixed organic layers used for organic photovoltaic applications have not been previously imaged using STEM tomography as there is insufficient contrast between donor and acceptor components. We generate contrast by substituting fullerenes with endohedral fullerenes that contain a Lu3N cluster within the fullerene cage. The high contrast and signal-to-noise ratio, in combination with use of the discrete algebraic reconstruction technique (DART), allowed us to generate the most detailed and accurate three-dimensional map of BHJ morphology to date. From the STEM tomography reconstructions we determined that three distinct material phases are present within the BHJs. By observation of the changes to morphology and mixing ratio that occur during thermal and solvent annealing, we are able to determine how mutual solubility and fullerene crystallization affect the formation of morphology and long term stability of the material mixture. This material/technique combination shows itself as a powerful tool for examining morphology in detail and allows for observation of nanoscopic changes in local concentration. This research was supported in part by Laboratory Directed Research & Development program atmore » PNNL. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy under contract DE-AC05-76RL01830.« less

Progress in electron tomography to assess the 3D nanostructure of catalysts

Abstract: The activity, selectivity and stability of solid catalysts depend critically on the details of their structure at all relevant length scales. Electron tomography (or 3D-TEM) has emerged as a powerful technique for nanostructural characterization. In this review we highlight recent advances in the field of electron tomography for the analysis of solid catalyst. Several examples demonstrate how unique quantitative information can be derived on relevant structural properties such as pore connectivity and corrugation, particle size distributions, and the 3D location of metal nanoparticles in porous oxide or carbon supports. The development of high-resolution imaging and novel reconstruction algorithms is promising to obtain atomically resolved electron tomograms of single catalyst nanoparticles. New reconstruction algorithms allow reconstruction from only a few projections, and hold potential for analyzing beam sensitive samples, as well as for time resolved electron tomography. Element specific or ‘chemical’ electron tomography, using electron energy-loss (EELS) or energy-dispersive X-ray spectroscopy (EDX), is an emerging tool for obtaining both chemical and structural information at nanoscale resolution. The rapid progress in electron tomography over the past few years holds great promise for detailed and quantitative insight into relevant nanostructural properties, thus allowing us to further develop our understanding of the relation between nanostructure and performance for catalysts and related materials.

Electron tomography resolves a novel crystal structure in a binary nanocrystal superlattice.

Abstract: The self-assembly of different nanocrystals into a binary superlattice is of interest for both colloidal science and nanomaterials science New properties may emerge from the interaction between the nanocrystal building blocks that are ordered in close contact in three dimensions Identification of the superlattice structure including its defects is of key interest in understanding the electrical and optical properties of these systems Transmission electron microscopy (TEM) has been very instrumental to reach this goal but fails for complex crystal structures and buried defects Here, we use electron tomography to resolve the three-dimensional crystal structure of a binary superlattice that could not be resolved by TEM only The structure with a [PbSe]6[CdSe]19 stoichiometry has no analogue in the atomic world Moreover we will show how tomography can overcome the clouding effects of planar defects on structure identification by TEM

Chapter 11 – Correlative Microscopy

Abstract: Correlative microscopy is a method when for the analysis of the very same cell or tissue area several different methods of light or electron microscopy are used. Usually these methods of analysis are separated by the period of additional preparation. Traditionally, LM and EM observations are carried out in different populations of cells/tissues. In biology, light microscopy (LM) is usually used to study phenomena at a global scale and to look for unique or rare events for their subsequent examination under the electron microscope. This combination provides an opportunity for live imaging with subsequent electron microscopic analysis of the very same sample, which provides the convenience and the velocity of light microscopy with the very high level of resolution of electron microscopy. Unfortunately, observation of living cells under EM is still impossible. The advent of true correlative light-electron microscopy (CLEM) has allowed high-resolution imaging by EM of the very same structure observed by LM. This chapter describes imaging with the help of CLEM. The guidelines presented herein enable researchers to analyze structure of organelles and in particular rare events captured by low-resolution imaging of a population or transient events captured by live light imaging can now also be studied at high resolution by EM.

Where bone meets implant: the characterization of nano-osseointegration.

Abstract: The recent application of electron tomography to the study of biomaterial interfaces with bone has brought about an awareness of nano-osseointegration and, to a further extent, demanded increasingly advanced characterization methodologies. In this study, nanoscale osseointegration has been studied via laser-modified titanium implants. The micro- and nano-structured implants were placed in the proximal tibia of New Zealand white rabbits for six months. High-resolution transmission electron microscopy (HRTEM), analytical microscopy, including energy dispersive X-ray spectroscopy (EDXS) and energy-filtered TEM (EFTEM), as well as electron tomography studies were used to investigate the degree of nano-osseointegration in two- and three-dimensions. HRTEM indicated the laser-modified surface encouraged the formation of crystalline hydroxyapatite in the immediate vicinity of the implant. Analytical studies suggested the presence of a functionally graded interface at the implant surface, characterized by the gradual intermixing of bone with oxide layer. Yet, the most compelling of techniques, which enabled straightforward visualization of nano-osseointegration, proved to be segmentation of electron tomographic reconstructions, where thresholding techniques identified bone penetrating into the nanoscale roughened surface features of laser-modified titanium. Combining high-resolution, analytical and three-dimensional electron microscopy techniques has proven to encourage identification and understanding of nano-osseointegration.

Development of an environmental high-voltage electron microscope for reaction science

Abstract: Environmental transmission electron microscopy and ultra-high resolution electron microscopic observation using aberration correctors have recently emerged as topics of great interest. The former method is an extension of the so-called in situ electron microscopy that has been performed since the 1970s. Current research in this area has been focusing on dynamic observation with atomic resolution under gaseous atmospheres and in liquids. Since 2007, Nagoya University has been developing a new 1-MV high voltage (scanning) transmission electron microscope that can be used to observe nanomaterials under conditions that include the presence of gases, liquids and illuminating lights, and it can be also used to perform mechanical operations to nanometre-sized areas as well as electron tomography and elemental analysis by electron energy loss spectroscopy. The new instrument has been used to image and analyse various types of samples including biological ones.

Peptide-Conjugation Induced Conformational Changes in Human IgG1 Observed by Optimized Negative-Staining and Individual-Particle Electron Tomography

Abstract: Peptides show much promise as potent and selective drug candidates. Fusing peptides to a scaffold monoclonal antibody produces a conjugated antibody which has the advantages of peptide activity yet also has the pharmacokinetics determined by the scaffold antibody. However, the conjugated antibody often has poor binding affinity to antigens that may be related to unknown structural changes. The study of the conformational change is difficult by conventional techniques because structural fluctuation under equilibrium results in multiple structures co-existing. Here, we employed our two recently developed electron microscopy (EM) techniques: optimized negative-staining (OpNS) EM and individual-particle electron tomography (IPET). Two-dimensional (2D) image analyses and three-dimensional (3D) maps have shown that the domains of antibodies present an elongated peptide-conjugated conformational change, suggesting that our EM techniques may be novel tools to monitor the structural conformation changes in heterogeneous and dynamic macromolecules, such as drug delivery vehicles after pharmacological synthesis and development.

3D Chemical Mapping of PEM Fuel Cell Cathodes by Scanning Transmission Soft X-ray SpectroTomography

Abstract: Knowledge of the spatial distribution and organization of chemical components in membrane electrode assemblies (MEA) of proton exchange membrane fuel cells (PEM-FC) is essential for developing optimal materials and fabrication methods Depending on fabrication, inhomogeneities of components (carbon supports, catalyst nanoparticles, and ionomer polymers) can happen either intentionally, or unintentionally. The resulting component mismatches may cause complications for producing the optimal pore network for gas/liquid transport, ionomer coatings for proton and oxygen transport, and can affect the overall reaction rate (efficiency) and degree of component degradation. The length scales of cathodes, membranes and anodes (1-10 μm), make chemical microanalysis of catalyst coated membranes (CCMs) challenging. 2D projection imaging by transmission electron microscopy (TEM) and scanning transmission soft-X-ray microscopy (STXM) [1] are able to characterize the chemical structure of CCMs on spatial scales from nanometers to microns. However, the optimal CCM structures are 3D in character and thus a tomography or a spectro-tomography [2] approach, which provide a 3D microanalysis of the fuel cell components, is preferred. Electron beam or electron tomography (ET) [3] and hard X-ray or micro computed tomography (μ-CT) [4] have been applied for characterizing fuel cell materials. Tomography without a spectroscopic dimension has limitations in differentiating the components of the sample. Segmentation procedures which are used to differentiate materials are based on differences in the electron or X-ray absorption. However these are the product of the material and the thickness. Usually, both are unknown. Thus, segmentation is typically only successful for very different classes of materials like carbon (GDL, MPL, and carbon support) versus air, or carbon versus metal (Pt). To complement the existing electron and hard X-ray microtomography techniques we have developed soft X-ray spectro-tomography [2] as a means to produce chemically sensitive 3D maps. Using STXM [4] we produce series of images at selected photon energies at a series of rotational angles of the sample. The rotational series are tomographically reconstructed, while the energy variation is reduced to quantitative chemical information. We used STXM5.3.2.2 at the Advanced Light Source for imaging ~150 nm thick CCM cathode samples prepared by focused ion beam (FIB, sample A) and ultramicrotomy (sample B). The STXM samples were mounted on a rotational holder with 360 range and 0.1 degree resolution. Images were acquired at a discreet number of energies, which were chosen to differentiate carbon support, catalyst, and ionomer, based on previous study of the NEXAFS spectra for CCM components [5-7]. At 4 intervals over the angle range -56 to +40 a stack of four images in the C 1s edge (278, 285.4, 292.4, 300 eV) were recorded for sample A. For sample B, a stack of two images at the F1s edge (684, 694 eV) were recorded at 3 intervals over the angle range -30 to +60. Each acquisition took ~6 h with a ~30% duty cycle, due to need to manually adjust sample positioning. The images in each energy stack were aligned, converted to the OD scale and chemical maps were constructed for the catalyst, carbon support and the ionomer for sample A; and the carbon support and the ionomer or sample B, respectively. The set of chemical component maps over the angular range were processed using typical tomography analysis procedures (image alignment, 3D reconstruction and visualization) using a variety of reconstruction methods included in the public software tools TOMOJ and ImodJ aiming for the best geometrical representation of the samples. The final analysis of the 3D maps of different components was performed using Amira. These 3D chemical maps demonstrate that chemically sensitive 3D maps of CCM samples can be derived using STXM spectro-tomography. Currently, the method has been able to differentiate and map the carbon support and ionomer in the CCM cathode, as well as to visualize the pore network, within the spatial resolution of the STXM method (~30 nm). [8]

Acquisition parameters optimization of a transmission electron forward scatter diffraction system in a cold-field emission scanning electron microscope for nanomaterials characterization.

Abstract: Transmission electron forward scatter diffraction (t-EFSD) is a new technique providing crystallographic information with high resolution on thin specimens by using a conventional electron backscatter diffraction (EBSD) system in a scanning electron microscope. In this study, the impact of tilt angle, working distance, and detector distance on the Kikuchi pattern quality were investigated in a cold-field emission scanning electron microscope (CFE-SEM). We demonstrated that t-EFSD is applicable for tilt angles ranging from -20° to -40°. Working distance (WD) should be optimized for each material by choosing the WD for which the EBSD camera screen illumination is the highest, as the number of detected electrons on the screen is directly dependent on the scattering angle. To take advantage of the best performances of the CFE-SEM, the EBSD camera should be close to the sample and oriented towards the bottom to increase forward scattered electron collection efficiency. However, specimen chamber cluttering and beam/mechanical drift are important limitations in the CFE-SEM used in this work. Finally, the importance of t-EFSD in materials science characterization was illustrated through three examples of phase identification and orientation mapping.

High resolution electron tomography

Abstract: Reaching atomic resolution in 3D has been the ultimate goal in the field of electron tomography for many years. Significant progress, both on the theoretical as well as the experimental side has recently resulted in several exciting examples demonstrating the ability to visualise atoms in 3D. In this paper, we will review the different steps that have pushed the resolution in 3D to the atomic level. A broad range of methodologies and practical examples together with their impact on materials science will be discussed. Finally, we will provide an outlook and will describe future challenges in the field of high resolution electron tomography.

Inclusion of radiation damage dynamics in high-resolution transmission electron microscopy image simulations: The example of graphene

Abstract: (Received 1 May 2012; revised manuscript received 11 September 2012; published 21 March 2013)Computer image simulations provide a crucial aid to high-resolution transmission electron microscopy(HRTEM) in gaining fundamental understanding of the structure of materials. Interpretation of HRTEM imagesis, however, complicated due to continuous structure deformation caused by the imaging electron beam. Acomputational methodology has been implemented that takes into account the effects of the electron beamon deformation of sample structure during observation and imaging in HRTEM. The evolution of the samplestructure is described as a sequence of externally initiated discrete damage events with a frequency determinedby the cross section, which depends on the energy of the electron beam. A series of images showing structureevolution with time is obtained by coupling molecular dynamics simulations with the image simulation. Thesesimulationpartsarelinkedbytwoexperimentalparameters:theenergyoftheelectronbeamandtheelectrondoserate. As the energy of the electron beam also determines resolution and contrast of the obtained HRTEM image,a careful selection of its value is required to achieve a fine balance between reduction of the sample damagecausedbytheelectronbeamandthequalityoftheacquiredimage.Theproposedcomputationalapproachisusedto simulate the recently observed process of structural transformation of a small graphene flake into a fullerenecage. The simulated series of images showing the evolution of a graphene flake under the 80 keV electron beamclosely reproduces experimental HRTEM images with regard to the structure evolution route, evolution rate, andsignal-to-noise ratio. We show that under the increased electron beam energy of 200 keV a similar observationwill be obscured by high damage rate or low signal-to-noise ratio.DOI: 10.1103/PhysRevB.87.094110 PACS number(s): 61

A new approach to the investigation of nanoparticles: Electron tomography with compressed sensing

Abstract: The principal purpose of this contribution is to illustrate the potential of compressed sensing electron tomography for the characterisation of nanoparticulate materials that are vulnerable to electron beam damage. Not only is there growing interest in nanoparticles of organic materials in medical and allied contexts, there is also the need to investigate nanoparticles and nanoclusters of metals supported on biological macromolecular entities in the context of drug delivery. A qualitative account of the principles of electron tomography is outlined with illustrations from the field of heterogeneous catalysis, where electron beam damage is less of an issue, and an appendix deals with more quantitative aspects of how compressed sensing promises to expand the range of samples that have hitherto been accessible to investigation.

Tracing the Migration History of Metal Catalysts in Metal-Assisted Chemically Etched Silicon

Abstract: Three-dimensional (3D) visualization of complex embedded nanopore networks in silicon requires expensive machinery and tedious sample preparation procedures such as electron tomography, also known as 3D transmission electron microscopy. In this article, we report a new, fast, powerful, and low-cost three-dimensional imaging technique with sub-5 nm resolution. This new imaging method is applied to metal-assisted chemically etched monocrystalline Si to demonstrate its capabilities. The AFEI (atomic layer deposition-fill-etch-imaging) technique consists of three simple process steps that are available in most material research settings. First the porous substrate is conformally coated with an atomic layer deposition (ALD) metal oxide layer. ALD is able to penetrate deep into complex, high aspect ratio pores, as it is a sequential gas-phase deposition process. Next, the cross-section of the ALD-filled porous Si substrate is etched with high-density fluorine-based plasma processing, which yields very high sele...

Electron tomography in soft materials

Abstract: This review summarizes the recent advances in electron tomography (ET) and its application to polymer nanostructures. Truly quantitative three-dimensional (3D) images of polymer nanostructures can now be obtained by reducing or eliminating the missing tilt range in ET experiments. The reduction of the resulting missing wedge provides sub-nanometer resolution, which is sufficiently small for soft materials. Because soft materials often exhibit hierarchical structures, observation of a large volume with edges several micrometers in length is important to capture the structural elements on a scale larger than tens of nanometers. The introduction of scanning optics to ET has made it possible to obtain 3D data from micrometer-thick polymer specimens by using conventional electron microscopes at a relatively low accelerating voltage of 200 kV. We present some examples of the structural analysis of soft materials, such as nanostructures of self-assembled block copolymers and fuel cell electrodes.