Frank Muecklich Saarland University
David Seidman Northwestern University
Yuich Ikuhara The University of Tokyo
Institute of Engineering Innovation
Paul Midgley University of Cambridge
Manfred Ruehle Max Planck Institute for Metals Research
Monday PM, November 28, 2011
Fairfax A (Sheraton)
9:30 AM - **PP1.1
Three-Dimensional Characterization of Nanostructures and Devices at the Atomic Scale Using Aberration-Corrected Electron Tomography.
David Muller 1 2 , Robert Hovden 1 Show Abstract
1 School of Applied Physics and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York, United States
A powerful approach to 3D imaging of materials and devices at the nanoscale has been by electron tomography, where the sample is imaged in projection in a series of different tilts and the tilt series is then reconstructed to produce a three-dimensional image. The development of aberration correctors has enabled a new generation of scanning transmission electron microscopes capable of forming sub-angstrom resolution probes and allowing high convergence angles where optical sectioning becomes an alternative strategy for forming three-dimensional images. Here we explore the physical limits to 3D chemical imaging using our corrected scanning transmission electron microscope (STEM), and investigate the possibility of hybrid methods that combine the strengths of both the tilting and optical sectioning approaches. By recording a through-focal series it is possible to reconstruct a 3D image with a 0.1x0.1x5 nm spatial resolution for single atoms, but with elongation factors of 30-50x in the vertical direction for finite objects. To do better, we must also perform a limited tilt series. The spatial resolution of a pure tilt series is limited to about 1 nm by the inability to accurately align the images on a sub-nanometer level, as well the finite sampling in Fourier space. However, by developing a hybrid algorithm to combine both methods, we can reduce the number of required tilt intervals and increase the depth resolution. With improved 3D reconstruction algorithms it is possible to obtain spatial resolutions below 1nm in all dimensions. Higher resolution is also possible by a-priori assumptions about the sample to restrict information and hence reduce the degrees of freedom in the problem. We discuss the scaling of these approaches for different classes of materials problems such as core-shell catalysts nanoparticle structures and dopants in semiconductor devices.
10:00 AM - **PP1.2
Optical Sectioning and Scanning Confocal Electron Microscopy for 3D Imaging and Analysis.
Peter Nellist 1 Show Abstract
1 Department of Materials, University of Oxford, Oxford United Kingdom
The development of aberration correctors for transmission electron microscopy (TEM) has allowed much larger numerical apertures to be used in electron optics, which leads to a reduction in depth of field. This reduced depth of field can be used to obtain information about specific depths in a sample, or to record a 3D data set in the form a focal series; an approach known as optical sectioning.In this presentation, I will review the various optical sectioning modes that have been explored in TEM. In particular I will review the forms of contrast that might be expected and the resolution limits of the technique. I will show that optical sectioning in a conventional TEM or scanning TEM (STEM) instrument always leads to a missing cone of information in the 3D transfer function resulting in longitudinal elongation of laterally extended objects in the image . Operating a microscope in a confocal mode to form a scanning confocal electron microscope (SCEM) can fill this missing cone, however such an approach requires an instrument fitted with aberration correctors both before and after the specimen.The SCEM imaging modes that have so far been implemented are bright-field SCEM, energy-filtered SCEM and annular dark-field SCEM. For bright-field SCEM, I will show that contrast only arises from multiple scattering, leading to complications in image interpretation. By recording the entire detector plane, however, depth sensitive diffraction patterns can be recorded which may allow 3D grain mapping . The energy-filtered SCEM mode offers a much simpler image contrast, and we demonstrate nanoscale elemental mapping in 3D . We will describe how chromatic aberration leads to a narrow energy window for mapping, which preserves the excellent depth resolution but leads to low signal to noise in images. I will also review interesting recent progress in annular dark-field SCEM. COSGRIFF, E. C., NELLIST, P. D., D'ALFONSO, A. J., FINDLAY, S. D., BEHAN, G., WANG, P., ALLEN, L. J. & KIRKLAND, A. I. 2010. Image Contrast in Aberration-Corrected Scanning Confocal Electron Microscopy. Advances in Imaging and Electron Physics, Vol 162.pp45-76. WANG, P., BEHAN, G., KIRKLAND, A. I., NELLIST, P. D., COSGRIFF, E. C., D'ALFONSO, A. J., MORGAN, A. J., ALLEN, L. J., HASHIMOTO, A., TAKEGUCHI, M., MITSUISHI, K. & SHIMOJO, M. 2011. Bright-field scanning confocal electron microscopy using a double aberration-corrected transmission electron microscope. Ultramicroscopy, 111, 877-886. WANG, P., BEHAN, G., TAKEGUCHI, M., HASHIMOTO, A., MITSUISHI, K., SHIMOJO, M., KIRKLAND, A. I. & NELLIST, P. D. 2010. Nanoscale Energy-Filtered Scanning Confocal Electron Microscopy Using a Double-Aberration-Corrected Transmission Electron Microscope. Physical Review Letters, 104, 200801.
10:30 AM - PP1.3
3-D Tracking and Visualization of Hundreds of Fuel Cell Nanocatalysts during Electrochemical Aging.
Yingchao Yu 1 , Huolin Xin 2 , Robert Hovden 3 , Deli Wang 1 , Hector Abruna 1 , David Muller 3 Show Abstract
1 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 2 Department of Physics, Cornell University, Ithaca, New York, United States, 3 School of Applied and Engineering Physics & Kavli Institute, Cornell University, Ithaca, New York, United States
One of the major cost barriers for the commercialization of low-temperature fuel cells is the rapid degradation of the nanocatalyst particles in the cathode. Much effort has been spent on the ex-situ study of particles after aging in a membrane-electrode-assembly (MEA, the power generating component of a fuel cell). In these experiments, the MEA needs to be sectioned for transmission electron microscopy observation. Therefore, the evolution trajectory of the particles is missing and thus it is difficult to unscramble the coarsening contribution of coalescence vs. Ostwald ripening. In addition, the 2-D images are often misleading as one cannot tell how the nanocatalyst particles are present on a 3-D carbon support. Here, we present a new approach in which one can identify hundreds of nanoparticles in 3-D with one-to-one correspondence before and after electrochemical aging. This enables the study of the coarsening evolution of the particles by tracking location changes on support surfaces, observing particle volume changes, and directly visualizing coalescence events. It allows us to answer questions such as how did the particles loose surface area, how did they move, was there a particle-support interaction, etc. This novel approach is performed on carrying out electrochemical (e-chem) experiments directly on a TEM support grid. A carbon-coated gold index grid was used as the working electrode in a three-electrode e-chem cell. The catalyst nanoparticles were sprayed on the grid prior to e-chem experiments. The grid contained indexed windows for locating specific regions of the specimen, allowing us to perform ADF-STEM tomography on exactly the same location before and after e-chem aging. The 3-D reconstruction results allow us to track particles one-by-one and uncover the coarsening mechanisms. We found that the majority of the coarsening events were caused by particle coalescence.
10:45 AM - PP1.4
3D Dopant Concentration in Femtosecond Laser-Doped Silicon Investigated by HAADF STEM Nanotomography.
Georg Haberfehlner 1 , Matthew Smith 2 , David Cooper 1 , Geoffroy Auvert 3 , Meng-Ju Sher 4 , Mark Winkler 4 , Eric Mazur 4 , Silvija Gradecak 2 , Narciso Gambacorti 1 , Pierre Bleuet 1 Show Abstract
1 , CEA-Leti, Grenoble France, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , STMicroelectronics, Crolles France, 4 Department of Physics, and 3. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Depositing a thin film onto a substrate prior to femtosecond (fs) laser irradiation is a flexible approach to novel materials synthesis, but the doping process is not well understood. Chalcogen femtosecond laser-doped silicon exhibits near-unity broadband absorption of visible and near infrared light and therefore is of great interest for photodetector and photovoltaic applications. It has been shown that post-process annealing (30 minutes, 500-900°C) decreases the IR-absorptance of chalcogen laser-doped silicon, likely due to a diffusive dopant relaxation mechanism. Questions remain, however, about the doping process, the resulting dopant distribution, and the relaxation of dopants with annealing. Understanding the thin-film fs-laser doping process and the subsequent dopant relaxation with annealing requires characterization techniques with nanometer resolution in three dimensions. While conventional methods provide only two-dimensional projections, electron tomography allows imaging in three dimensions with resolution of a few nanometer for samples with cross-sections of about 200nm, thus allowing to reproduce complex three-dimensional structures. In particular, electron tomography provides means to extract local information about the concentration and positioning of dopants as well as about the material's microstructure.Using Focused Ion Beam (FIB) we extracted needle-shaped samples of femtosecond laser-doped silicon with a diameter of ~200nm. The use of needle-shaped samples keeps the sample thickness along the electron beam path low for all tilt angles and allows a maximization of the tilt range, reducing thereby artifacts in the reconstruction.We used High-Angle Annular Dark Field Scanning TEM (HAADF STEM) tomography to map the selenium dopant distribution in femtosecond laser-doped silicon before annealing and after a 950°C anneal for 30 minutes. For crystalline samples HAADF STEM is especially well suited since diffraction contrast becomes negligible. Therefore the projection requirement is fulfilled and 3D reconstruction from a set of images taken at a large number of tilt angles becomes possible. Furthermore HAADF STEM is sensitive to the atomic number. Due to the larger atomic number of selenium compared to silicon, contrast changes in the reconstructed volume can be directly attributed to variations of the local dopant concentration. We show that before annealing the selenium dopants are distributed homogeneously throughout certain regions of the sample, and that the concentration is strongly a function of depth. The annealing process causes segregation at grain boundaries and the formation of selenium-rich precipitates with a diameter of about 20nm. Our results showcase the ability of HAADF STEM tomography to provide valuable information on the distribution of supersaturated dopants and their evolution with annealing.
11:30 AM - **PP1.5
Direct Imaging of Individual Dopant Atoms in Buried Crystalline Interfaces.
Naoya Shibata 1 , Scott Findlay 1 , Teruyasu Mizoguchi 1 , Yuichi Ikuhara 1 Show Abstract
1 , The University of Tokyo, Tokyo Japan
High angle annular dark field (HAADF) imaging in scanning transmission electron microscopy (STEM) is well suited to identifying heavy elements in lighter surrounds. This has been used to explore the detailed configuration of impurity atoms segregated at grain boundaries and interfaces in many ceramic materials, where such dopant addition can significantly changes the physical properties of the material. At best, a single image only gives a clear indication of the projected structure along one direction, but the complexity of interface structure makes it desirable to seek further information, such as individual dopant atom distribution across the interface plane. In the present study, we will show our recent results on the dopant atom segregation in alumina grain boundaries from high-angle to low-angle grain boundaries using HAADF STEM combined with density functional theory calculations. We will experimentally demonstrate and discuss the prospects for atomic-scale 3D imaging of individual dopant atoms in a buried crystalline interface, viewing the buried interface from its normal direction by HAADF STEM.
12:00 PM - PP1.6
Statistical Comparison of Various Tomographic Reconstruction Algorithms with Respect to Missing Wedge Artifacts.
Sebastian Lueck 1 , Andreas Kupsch 2 , Axel Lange 2 , Manfred Hentschel 2 , Volker Schmidt 1 Show Abstract
1 Institute of Stochastics, Ulm University, Ulm Germany, 2 , BAM Federal Institute of Materials Research and Testing, Berlin Germany
The presence of elongation, streak and blurring artifacts in tomograms recorded under a missing wedge of rotation angles represents a major challenge for the quantitative analysis of tomographic reconstruction data, which is especially relevant in electron tomography. Simple strategies to compensate for the elongation prior to image analysis are problematic, since the relative position of image objects of interest leads to local variations of blurring and streak intensity. We compare the missing wedge artifacts of standard reconstruction algorithms to the results obtained by the innovative reconstruction technique DIRECTT (Direct Iterative Reconstruction of Computed Tomography Trajectories) , which has been developed at the Federal Institute of Materials Research and Testing (BAM) in Berlin, and whose reconstruction principle will be explained. For the comparison of missing wedge artifacts we apply techniques from spatial statistics, which have been specifically designed to investigate the shape of phase boundaries in tomograms. More precisely, we statistically compare the rose of directions for the stochastic surface system formed by phase boundaries between phantom images and their tomographic reconstructions from simulated projections. In order to account for the stochastic effects of random object positioning on phase boundaries in complex material samples our study is based on randomized phantom data which is generated by models from stochastic geometry. We explore the capability of DIRECTT to reduce successfully missing wedge artifacts in comparison to standard algorithms under various degrees of imperfections in the virtual projections of the phantoms such as noise and the size of the missing wedge. Our results were obtained for DIRECTT reconstructions computed with the a priori information on the material composition to be approximately binary. In contrast to algorithms from discrete tomography, which have been previously shown to reduce missing wedge artifacts, this a priori knowledge was however only exploited during the first iteration steps. In the final iterations DIRECTT added details to the reconstructions without imposing restrictions on the choice of grayscales.
12:15 PM - PP1.7
Electron Tomography of Nanowires in the Scanning Electron Microscope.
Matteo Ferroni 1 2 , Andrea Migliori 3 , Vittorio Morandi 3 , Luca Ortolani 3 , Elisabetta Comini 1 2 , Giorgio Sberveglieri 1 2 Show Abstract
1 Department of Physics and Chemistry, University of Brescia, Brescia Italy, 2 IDASC, CNR, Brescia Italy, 3 IMM, CNR, Bologna Italy
This paper presents the capability of electron tomography in a Field-Emission SEM with STEM detector, and reports the application of this recently proposed 3-D imaging technique to nanosized specimens [1,2]. In the last years, electron tomography has been generally implemented in transmission electron microscopes, based on the signals from HAADF-STEM, Energy Filtered TEM, holography, and EDX mapping . More recently, the Scanning Transmission imaging mode has been implemented in scanning electron microscopes, taking advantage of some peculiar characteristics of the experimental set-up of the SEM . This low-energy counterpart of HAADF-STEM attains nanometric resolution and is free from aberrations caused by post-specimen imaging lenses .The significant improvement of the STEM detection system, through the optimization of detector design and performance together with the formulation of a tailored detection strategy, provides a direct-interpretable compositional image of the specimen . By varying the specimen-detector distance and the collection conditions of the STEM detector it is possible to collect transmitted electrons over as wide an angular range as 60°. In such a condition, the bright-field component of the transmitted electrons can be effectively separated from the dark-field one. This separation allows for a straightforward interpretation of the contrast in terms of local variations of composition or projected thickness.The capability of the SEM-STEM imaging mode to preserve the monotonical variation of the signal with specimen thickness meets the key requirement for tomographic reconstruction, and thus opens up the perspective for the 3-D reconstruction of nanosized samples. In addition, the large value for the maximum detection angle ensures a complete detection of the scattered electrons, even in case of relatively large specimen thickness. Thus, this detection strategy is capable to investigate specimen with large variation of projected thickness. In the case of tomography, these features are essential to maintain the proper image contrast when the specimen is rotated through the tilt series. The potential of the method has been demonstrated by implementing the system for specimen rotation in the SEM and acquiring a 120° tilt series of STEM images of ZnO nanowires. After reconstruction, the disposition of the wires, their uniform section and the tapered termination are properly retrieved by the tomographic reconstruction.REFERENCESM. Ferroni et al. 17th International Microscopy Congress - IMC17, September 19-24, 2010.P. Jornsanoh et al., Ulltramic. in press. P.A. Midgley et al. J. of Mic. 223 (2006) 185.S. Bals et al. Adv. Mat. 18 (2006) 292.P.G. Merli et al. Ultramicroscopy 88 (2001) 139.V. Morandi and P.G. Merli, J. Appl. Phys. 101 (2007) 114917.
12:30 PM - PP1.8
3D Visualisation of Crack Distributions in Oxidised Zirconium Alloys by FIB-Slicing.
Chris Grovenor 1 , Na Ni 2 , Sean Yardley 1 , Gareth Hughes 1 , Sergio Lozano-Perez 1 , John Sykes 1 Show Abstract
1 Department of Materials, Oxford University, Oxford United Kingdom, 2 Department of Materials, Imperial College, London United Kingdom
Zirconium alloys have been used as nuclear fuel cladding and structural fuel assembly components in nuclear reactors since the 1950s because of their low thermal neutron absorption cross-section, adequate corrosion resistance in high temperature water and reasonable mechanical properties. However, zirconium alloys show a characteristic periodic variation in oxidation rate and the development of a layered crack morphology during aqueous corrosion, and it is common to associate the first phenomenon with the appearance of the second.As part of a project to investigate the nano-scale chemistry and structure of the oxidation process, we have used 3D serial sectioning in a Zeiss NVision40 FIB to study the morphology and distribution of cracks in corroded ZIRLO samples at different stages of the oxidation process. Volumes of more than 1000 cubic microns can easily be analysed while maintaining spatial resolutions better than 40nm, and these volumes contain a large number of cracks and also much smaller second phase precipitates. We have shown that cracks are nucleated and grow at all stages of the oxidation process not just in sharp bursts at the kinetic transition as has been previously assumed. We have also been able to analyse the nucleation of cracks with reference to the local shape of the oxide/metal interface and the distribution of precipitates, will discuss these observations with reference to the mechanisms of oxide growth that control the useful lifetime of these materials in service.
Monday PM, November 28, 2011
Fairfax A (Sheraton)
2:30 PM - **PP2.1
Cryo Electron Microscopy of Biological Materials.
Wolfgang Baumeister 1 Show Abstract
1 Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried Germany
Today, essentially all electron microscopy of biological materials aiming for molecular resolution is cryo electron microscopy. Samples are examined in a frozen-hydrated state to avoid artifacts resulting from dehydration or from chemical fixation and staining. Three different imaging modalities are used: Electron crystallography, which can provide atomic resolution structures but requires that the molecules under study form well-ordered two-dimensional crystals. Single particle analysis which is the method of choice for large multi subunit protein complexes; in conjunction with other methods (‘hybrid methods’) it can provide structures with pseudo-atomic resolution. Electron tomography allows to study large (non-repetitive) structures, such as organelles or cells, and to analyze molecular structures in situ, i.e. in their unperturbed functional environments.The presentation will focus on single particle analysis and cryo electron tomography of supramolecular and cellular structures. Using the 26S proteasome, a molecular machine of 2.5 MDa, as an example it will be shown how a medium resolution structure of approx. 7 Å can be ‘upgraded’ by the integration of high-resolution structures of components and by the use of experimental restraints.In cryo electron tomography the main challenges are sample preparation and the molecular interpretation of tomograms with a poor signal-to-noise ratio. Denoising, automated segmentation, pattern recognition, and subtomogram averaging are the key strategies in tomogram interpretation. Focused ion beam technology is an emerging tool in the micromachining of frozen-hydrated samples. In conjunction with correlative fluorescence microscopy allowing the navigation of complex samples, thin lamellae suitable for tomography can be produced in a targeted manner.
3:00 PM - **PP2.2
Electron Tomography on Polymeric Self-Assembling Structures.
Hiroshi Jinnai 1 2 Show Abstract
1 , Institute for Materials Chemistry and Engineering (IMCE), Kyushu University, Fukuoka Japan, 2 , Japan Science and Technology Agency, ERATO, Takahara Soft Interfaces Project, Fukuoka Japan
Block copolymers, consisting of multiple, chemically dissimilar sequences covalently linked together, exhibit highly periodic nano-scale structures. The block copolymer self-assembly often shears common physical background with the self-assembling structures in microemulsions. In addition to the well-known block copolymer structures, e.g., lamellar, cylindrical, spherical and bicontinuous structures, much more complicated structures such as a double-helical structure of an amorphous, achiral ABC-type triblock terpolymer have been recently found. It is, however, still an open question how those block copolymers can self-assemble such complex three-dimensional (3D) morphology, especially from the molecular point of view. The luck of such fundamental knowledge is mainly due to the uncertainty in determining morphologies; Most of the structural studies and interpretations of the self-assembled structures, so far, have been based on two-dimensional (2D) electron micrographs.We will present a structural study of double helical morphology of poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) as an example in order to demonstrate how the 3D nano-scale imaging technique, transmission electron microtomography (TEMT), can be effectively used in the soft matter physics. The self-assembled structures in confined spaces and morphological transitions between structures upon changing temperature/pressure, often called an “order-order transition (OOT)”, are another interesting topics in the polymer physics field. In the former, the interplay between the imposed curvatures (by the confinement) and the intrinsic interfacial curvature due to the block copolymers determines the final morphology. The resulting morphologies are often very complicated and thus are quite difficult to ascertain. TEMT plays a crucial role to resolve such problems. In the OOT, the dynamical processes of structural transformation from one morphology to the other can be evaluated by closely examining the 3D “frozen” boundary structures between the pre-existing and evolving morphologies during the transition.
3:30 PM - **PP2.3
Low Temperature STEM Tomography of Catalytic Materials.
Nobuo Tanaka 1 , Kenta Yoshida 1 2 Show Abstract
1 Nanomaterials Division, EcoTopia Science Institute, Nagoya University, Nagoya, Aichi-prefecture, Japan, 2 Nanostructure laboratory, Japan Fine Ceramics Center, Nagoya, Aichi-prefecture, Japan
Three-dimensional structure analysis of heterogeneous particles is one of the next targets of electron microscopy, because it is closely related to the innovative research of batteries, fuel cells and solar cells as well as high-performance photo-catalysts. There are various kinds of methods developed for 3D observation in electron microscopy, which shall be discussed in the present session such as conventional tomography(CT), STEM observation along multiple zone axes and “z-slice method” using the finite intensity distribution of STEM probe along the optical axis. Although the principles are almost established, but the actual data acquisition and handling are not still straightforward to obtain the final 3D reconstruction and quantitative data particularly on small particles. We need to acquire more than 100 images with less electron irradiation damage. Automated data processing is also essentially important for connecting the data with the actual innovation. We have been using STEM tomography in a He-cooled 300 kV STEM(Tecnai: Polara) and self-developing the software for the quantitative analysis on surface areas, distribution of diameter of catalyst substrates such as TiO2 and CeO2 and area-distribution of gold or platinum clusters. In the present talk, the details of actual 3D electron microscopy and data analysis are presented enough that people interested in the field could catch up the present state of art.J. Yamasaki, N. Baba, H. Kakibayashi, O. Terasaki and N. Tanaka, Philo. Mag. 84(2004), 2819.S. Sueda, K. Yoshida and N. Tanaka: Ultramicroscopy, 110(2010), 1120
4:30 PM - PP2.4
Cryo-Electron Tomography: Three-Dimensional Imaging of Soft Matter.
Nico Sommerdijk 1 , Heiner Friedrich 1 , Beulah McKenzie 1 2 , Paul Bomans 1 , Fabio Nudelman 1 , Bert De With 1 , Simon Holder 2 Show Abstract
1 Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven Netherlands, 2 School of Physical Sciences, University of Kent, Canterbury United Kingdom
For the analysis of solution-born nanostructures and in particular self-organizing systems the use of cryo-TEM is a growing field. Where cryo-electron tomography (cryo –ET) is currently developing as a major technique in life sciences, its application in the study of non-biologic materials is still virtually unexplored. Nevertheless, this technique has been proven instrumental in understanding issues such as macromolecular self-assembly, the organization of molecules at interfaces and template-directed mineralization[5-7]. Following initial reports on internally-structured micelles from amphiphilic block copolymers, we recently reported the formation of micelles with thermally-tunable bicontinuous internal structure from semi-crystalline amphiphilic block copolymers. Here, the use of cryo electron tomography (cryo-ET) was essential for the characterization of the internal structure of the assemblies in particular with regard to compartment size, morphology, connectivity and accessibility. We show that these aggregates possess a high internal order similar and that their internal structure totally reorganizes above the melting point of the crystalline block.Cryo-ET acquisition using the TU/e cryoTITAN microscope was optimized by limiting the accumulated dose to less than 70 e-/A2 and adjusting the exposure time with tilt (I/I0=1.6). Datasets were alignment and reconstructed in Inspect3D and IMOD and optimized exploring different reconstruction algorithms (WB, SIRT, ART). The challenge ahead lies in segmenting and quantifying the reconstructions to develop a comprehensive understanding of the self assembly process.  H. Friedrich, et al, Angew. Chem. Int. Ed. 49, 7850 (2010). F. Nudelman, et al., Soft Matter 7, 17 (2011) A.L. Parry, et al. Angew. Chem. Int. Ed. 47, 8859 (2008). M.R.J. Vos, et al. J. Am. Chem. Soc. 129, 11894 (2007). E.M. Pouget, et al, Science, 323, 1455 (2009). F. Nudelman, et al, Nature Mater, 9, 1004 (2010) A. Dey, et al, Nature Mater, 9, 1010 (2010). B.E. McKenzie, et al, J. Am. Chem. Soc. 132, 10256 (2010).
4:45 PM - PP2.5
Three-Dimensional Characterization of Chemical Intermixing in Nano-Layered Radiation Shielding Metallic Thin Films.
Arun Devaraj 1 , Rama Shesha Vemuri 1 2 , Tamas Varga 1 , Shutthanandan Vaithiyalingam 1 , Satyanarayana V Kuchibhatla 1 , Mark Engelhard 1 , Ponnusamy Nachimuthu 1 , Charles Henager 1 , Chongmin Wang 1 , Suntharampillai Thevuthasan 1 Show Abstract
1 Environmental Molecular Science laboratory, Pacific Northwest National lab, Richland, Washington, United States, 2 Department of Materials Science and Engineering, University of Texas at El Paso, El Paso, Texas, United States
The design of radiation damage tolerant materials relies on the high density of interfaces that can act as effective traps and recombination centers for the radiation-induced vacancies and interstitials. The work presented is an integrated experimental and computational modeling effort to understand the atomic structure of the interfaces in layered metallic thin films before and after the ion beam irradiation using the state of the art characterization and computational modeling tools available in Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory. Nanoscale Al/Ti multilayer thin films were fabricated on Si (100) and epi polished MgO (100) substrates by DC magnetron sputtering at room temperature. The fabricated metallic multilayer samples were irradiated using 1 MeV Au+ ions. The results obtained by three dimensional atom probe tomography (APT) of the pure and irradiated nanolayered Al/Ti thin films were compared with the results from high resolution TEM/ HAADF STEM, Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy (XPS). The unique benefits of APT in characterizing the chemical intermixing in multilayer thin films with rough interfaces will be highlighted. Detailed characterization was carried out to develop an in-depth understanding of the interface damage, crystal lattice damage, amorphization and defect density in the post and pre ion irradiation samples of Al/Ti multilayer thin films. These insights were used to investigate whether the internal interfaces in metallic multilayers can be manipulated at the nanoscale to enhance dynamic recombination of radiation-produced defects, or self-healing, so as to reduce radiation damage without compromising other properties.
5:00 PM - PP2.6
Tomography of Multilayered Materials for Optoelectronic Applications.
Lluis Yedra 1 , Sonia Estrade 1 2 , Jose Manuel Rebled 1 , Zarco Gacevic 3 , Sergio Fernandez-Garrido 3 , Enrique Calleja 3 , Hamed Heidari 4 , Bart Goris 4 , Sara Bals 4 , Francesca Peiro 1 Show Abstract
1 Electronics Department, University of Barcelona, Barcelona Spain, 2 Scientific and Technical Center, University of Barcelona, Barcelona Spain, 3 ISOM, Universidad Politécnica de Madrid, Madrid Spain, 4 EMAT, University of Antwerp, Antwerp Belgium
Nanostructured semiconductor multilayer materials have gained interest in recent years due to their potential applications in optoelectronics, microelectronics and photonics. The configuration and regularity of these heterostructures can greatly affect the functional properties of the final device. Nevertheless, layers which appear smooth in conventional TEM cross sections might be irregular in some unknown direction. Electron Tomography using needle-shaped samples and high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) makes it possible to analyze the structure and chemistry of the layers in every direction. This approach is therefore a very appropriate tool to characterize the regularity of these multilayer stacks.In this work, electron tomography has been applied to evaluate the quality of a multilayer system for photonic and optoelectronic applications. Ten periods InAlN/GaN distributed Bragg reflectors (DBRs), optimised to center light reflection at a wavelength of 400 nm, were analyzed. The presence of an intermediate In-rich InAlN layer at each InAl-GaN interface has been assessed by STEM-HAADF Tomography. Tomographic reconstruction was carried out on a needle shaped sample out of a tilt series covering a range of 70 to -70 degrees at 2 degrees tilt step. The 3D reconstruction showed the regular thickness and smoothness of all layers.
5:15 PM - PP2.7
S/TEM Tomography of γ-Al203 Morphology and Pt Anchoring.
Libor Kovarik 1 , Ja Hun Kwak 2 , Arda Genc 3 , Janos Szanyi 2 , Chongmin Wang 1 , Charles Peden 2 Show Abstract
1 Environmental Molecular Science Laboratory, Pacific Northwest National Lab, Richland, Washington, United States, 2 Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington, United States, 3 , FEI company, Hillsboro, Oregon, United States
High surface-area γ-Al203 is extensively used as a catalyst and catalytic support material. Therefore the nature of γ-Al203 surfaces and how the catalytically active metals/oxides/sulfides anchor to γ-Al203 have a significant influence on the overall catalytic performance. In this work we analyze the morphology, the nature of surfaces and Pt anchoring on γ-Al203, which was synthesized in the shape of rhombohedra platelets. Single-tilt tomography in conventional Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) with High Angle Annular Dark Field Detector (HAADF) is the primary experimental technique employed. The electron microscopy observations are performed on FEI Titan 80-300 equipped with CEOS Cs –probe corrector operated at 300kV. Conventional TEM tomography was essential in establishing the differences between internal (porosity) and the external surfaces. It can be shown that these surfaces are not crystallographically equivalent: the external surfaces are crystallographically defined in terms of (110)Al2O3 and (111) Al2O3, whereas the internal surfaces have an additional (100)Al2O3. Complimentary STEM tomography enabled a detailed quantification of Pt anchoring to the external surfaces. The importance of these findings will be discussed in the context of catalytic performance and the phase transformation in transition aluminas.
5:30 PM - **PP2.8
3-Dimensional Imaging of Dislocation Microstructures by Electron Beams.
Jonathan Barnard 1 Show Abstract
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
This presentation will review the development of dislocation tomography in the transmission electron microscope over the past five years since its inception in 2006. This technique uses diffraction contrast caused by dislocation strain fields that, surprisingly, can be reconstructed tomographically despite the non-monotonicity of diffraction contrast generally. I will examine the merits of using both the conventional dark-field imaging in the conventional TEM (CTEM-DF) and the annular dark-field imaging mode in the scanning TEM (STEM-ADF). Further, the question of dislocation fidelity in the reconstructed volume will be addressed, including the effects of material anisotropy and reconstruction artefacts associated with poor tilt-axis/diffracted beam alignment. Examples of dislocation tomography will be presented, showing how dislocation microstructures can be fully recovered in both semiconducting and metallic systems, including mechanically deformed materials. The current limitations of dislocation tomography with conventional sample geometries and specimen holders will also be explored, with several avenues of development outlined.
PP3: Poster Session
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
9:00 PM - PP3.1
STEM Tomography of Highly Ordered Mesoporous Cobalt Oxide, Nickel Oxide, Cobalt and Nickel.
Amy Grano 1 , Johnny Goodwin 2 , Franchessa Sayler 1 , Jan-Henrik Smatt 3 , Martin Bakker 1 Show Abstract
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Central Analytical Facility, The University of Alabama, Tuscaloosa, Alabama, United States, 3 Physical Chemistry, Abo Akademi University, Turku Finland
Sol-gel synthesis utilizing block co-polymer templates is an effective method of producing highly ordered mesoporous materials, particularly ordered mesoporous silica. Such materials can then be used as hard templates for nanocasting, in which a variety of replication processes are utilized to produce mesoporous carbons and metal oxides. These processes are not limited to particles or thin films, but can also be used to produce samples with volumes exceeding 1 cubic centimeter. We have recently demonstrated that nanocasting can also be used to generate mesoporous metals including silver, cobalt, nickel and copper, in macroscopic samples. Removal of the silica template yields free-standing materials if the nanostructure is 3-dimensional in nature.We report here on a STEM/TEM tomography study of ordered mesoporous cobalt and nickel metals and their oxides formed by replication of SBA-15 mesoporous silica templates. SBA-15 silica consists of ordered arrays of 5-7 nm diameter pores. TEM tomography of platinium nanocast into particles of this material has previously established the presence of small (ca. 1 nm diameter) micropores in the walls of the silica that can generate free-standing, 3-dimensional replicas.
9:00 PM - PP3.10
Atom Probe Tomography Study of Grain Boundary Segregation in Super Duplex Stainless Steels Processed by High-Pressure Torsion.
Saritha Samudrala 1 , Yang Cao 2 , Michael Moody 1 , Megumi Kawasaki 3 , Xiaozhou Liao 2 , Terence Langdon 3 , Julie Cairney 1 Show Abstract
1 Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales, Australia, 2 School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales, Australia, 3 Departments of Aerospace and Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, California, United States
High-pressure torsion (HPT) is an effective method to produce bulk ultrafine-grained (<1 μm) and nanocrystalline (<100 nm) metallic materials. Processing super duplex stainless steels (SDSS) by HPT dramatically improves the strength, enhancing their already attractive combination of mechanical and corrosion properties for marine and petrochemical applications. In these multiple component alloys, the segregation of certain atomic species to the grain boundaries is likely to play a major role in determining the final grain size and the grain size stability, both of which play a vital role in the applicability of these new alloys.In this paper we investigate the grain boundary segregation in commercial DP3W super duplex stainless steel samples processed in the lab by HPT by using atom probe tomography (APT) and compare those to the cold rolled SDSS samples. Detailed compositional analysis is carried out (using peak deconvolution methods), showing significant segregation of Mo, P, C and B at the grain boundaries. Quantitative interfacial excess values are calculated from compositional profiles for these species. Small precipitates are also observed that are not easily discerned using transmission electron microscopy (TEM). This segregation appears to play an important role in stabilizing the microstructure of these samples due to the presence of a very high density of shear strains. Furthermore an understanding of the solute segregation at the grain boundaries provides valuable information on the solute balance within the grain and the significance of any precipitation behavior, which may be useful in future alloy design.
9:00 PM - PP3.12
Three-Dimensional Confocal Imaging of the Structure and Mobility of Grain Boundaries in Colloidal Crystals.
Eric Maire 1 3 , Maria Persson-Gulda 1 , David Weitz 2 , Frans Spaepen 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 CNRS-INSA, Universite-Lyon, Villeurbanne France, 2 Department of physics, Harvard University, Cambridge, Massachusetts, United States
Understanding and controlling the structure and evolution of grain boundaries is one of the central tasks of materials science. Studying the dynamics of grain boundaries at the atomic level is not easy, as atoms are difficult to visualize individually. To aid in this, we used crystalline colloidal suspensions as model systems. The particles used in this study interact as hard spheres and can be imaged in three dimensions (3D) using confocal microscopy. When these particles sediment onto a flat, featureless surface, they form columnar poly-crystals with close-packed planes parallel to the surface. When they sediment onto a glass slide in which a hole pattern has been created by micro-lithography, they can be made to form designed bi-crystals. The purpose of the paper is to show how these controlled crystals can be grown and imaged in 3D using confocal microscopy. Using 3D image processing of the data, we finally perform measurements such as the mobility of the boundaries and the shape of boundary grooves at the surface.
9:00 PM - PP3.2
Quantitative STEM Tomography of Layer-by-Layer Polymer-Au Nanocomposite Structures to Measure Plasmonic Coupling Behavior.
Nabil Bassim 1 , Andrew Herzing 2 , Joshue Caldwell 1 , Walter Dressick 1 , Kathryn Wahl 1 , Dmitri Petrovykh 3 , Kenan Fears 1 , Rhonda Stroud 1 Show Abstract
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 , National Institute of Standards & Technology, Gaithersburg, Maryland, United States, 3 , International Iberian Nanotechnology Laboratory, Braga Portugal
Nanocomposite multilayered thin film architectures comprising polyelectrolytes and Au nanoparticles are an attractive platform for designing customized coatings for plasmonic sensing applications. We studied coatings prepared via layer-by-layer (LbL) assembly of the oppositely-charged polyelectrolytes, polyallylamine hydrochloride (PAH) and sodium polystyrene sulfonate (PSS), deposited from various salt solutions to control film morphology, with the addition of regularly interspaced layers of ~15-nm Au-citrate nanoparticles. Changing the salt counterion in the polyelectrolyte solutions from singly (Cl-) to doubly charged (SO42-) species during film deposition altered not only the nanocomposite thickness and morphology, but also film uniformity and the Au nanoparticle packing and clustering. The internal structure of the films, in particular the distribution of Au particles and regularity of interparticle spacing within each layer, can have strong effects on plasmonic coupling within the film. Conventional cross-sectional transmission electron microscopy (TEM) allows inspection of the multilayer layer uniformity but not interparticle spacing within the Au layers. We have performed scanning transmission electron microscopy (STEM)-based tomography in an aberration-corrected STEM to evaluate the interparticle spacing and distribution within the Au layers. Slices extracted from the resulting electron tomogram were used to inspect the in-plane particle distributions, which were found to be highly dependent on the valency of the anions in solution during the deposition step. In general, the layer roughness, layer spacing and in-plane Au particle packing increased for samples deposited from polyelectrolyte solutions with the divalent anion SO42-, relative to solutions with monovalent Cl- anions. The ordering present in the PAH/PSS/Au films differed markedly between films deposited from solutions with Cl- and SO42- anions: the former were evenly dispersed and well-defined, while the latter exhibited irregular particle spacing and in many cases particles appear to have agglomerated into larger structures. The tomogram was used to estimate the area fraction of Au particles in each layer and to provide statistics about particle-particle spacing in both types of layers. These were then correlated to UV-Vis spectroscopy and revealed plasmonic shifts to ≈600 nm in films deposited from solutions containing sulfate anions and little plasmonic shift or coupling (resonance at ≈530 nm) in films deposited from solutions with chloride anions. Tomographic data provides useful guidelines towards designing tunable chemical sensors based on plasmonic coupling.
9:00 PM - PP3.5
HAADF STEM Tomography of Ferrimagnetic FexCo(2-x)O4 Nanostructures Embedded in Highly Ordered Antiferromagnetic Co3O4 Mesoporous Templates.
Lluis Yedra 1 , Sonia Estrade 1 2 , Eva Pellicer 3 , Moises Cabo 3 , Alberto Lopez-Ortega 4 , Marta Estrader 4 , Josep Nogues 5 , Dolors Baro 3 , Zineb Saghi 6 , Paul Midgley 6 , Francesca Peiro 1 Show Abstract
1 Electronics Department, University of Barcelona, Barcelona Spain, 2 Scientific and Technical Center, University of Barcelona, Barcelona Spain, 3 Departament de Fisica, Universitat Autonoma de Barcelona, Bellaterra Spain, 4 , CIN2(CIN-CSIC) and Universitat Autonoma de Barcelona, Catalan Institute of Nanotechnology, Bellaterra Spain, 5 , Institucio Catalana de Recerca i Estudis Avançats (ICREA) and Centre d'Investigacio en Nanociencia i Nanotecnologia (ICN-CSIC), Bellaterra Spain, 6 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Highly ordered mesoporous materials are gaining interest due to their high surface to volume ratio ant hence their potential applications in a broad range of fields. In this work we present the structural characterization of a series of antiferromagnetic (AFM) Co3O4 templates, nanocast replicas of mesoporous KIT-6 silica, filled with ferrimagnetic (FiM) (FexCo(2-x)O4). This novel concept allows increased versatility because of the AFM-FiM exchange interactions as well as the synergic combination of properties of both constituents. High-angle annular dark field (HAADF) tomography in the transmission electron microscope in scanning mode (STEM) was here used in order to assess the ability of different amounts of iron precursor to impregnate the structure of the Co3O4 templates.3D reconstruction of the tilted series, acquired for the host Co3O4 structure and for two different infiltration loadings, provided understanding of the interlaced structure of the mesoporous KIT-6 replicas and allowed to assess their high structural regularity. The pore size decreased as the amount of Fe-precursor increased, which suggests the growth of nanotubes within the Co3O4 channels, and it was observed that the iron precursor infiltration ability reaches a plateau as the Fe incorporation saturates before completely filling the pores. At higher charges, the iron oxide grew outside of the original framework.
9:00 PM - PP3.7
Atom-Scale Characterization of the Chemistry and Structure of Material Transfer onto AFM Tips Resulting from Nanoscale Contact and Sliding Experiments.
Christopher Tourek 1 , Sriram Sundararajan 1 Show Abstract
1 Mechanical Engineering, Iowa State University, Ames, Iowa, United States
While atomic force microscopy (AFM) based techniques have provedvery useful in investigating nanoscale phenomena, a detailed assessment of the material structure and chemistry of the near apex region of the AFM tip can provide further insights. Specific areas that would directly benefit from this information include fabrication and friction/wear studies using AFM tips where material transfer and tip chemistry are of importance. Few techniques exist that can provide this critical information. We present our investigations utilizing atom probe tomography to successfully study the near apex regions of an AFM tip at the atomic scale. Further we report our initial observations on the formation of transferred material during dry sliding experiments involving a commercially available Si AFM tip on Cu. The effects of sliding distance and normal load on the formation of transferred material are also reported. The reported technique opens up a new avenue of investigation for AFM-related materials research.
9:00 PM - PP3.8
Advances in Instrumentation and Applications for Atom Probe Tomography.
David Larson 1 , Peter Clifton 1 , Dan Lawrence 1 , David Olson 1 , Ty Prosa 1 , Rob Ulfig 1 , Joe Bunton 1 , Dan Lenz 1 , David Reinhard 1 , Jesse Olson 1 , Thomas Kelly 1 Show Abstract
1 , Cameca Instruments Inc., Madison, Wisconsin, United States
Hardware and software innovations have been incorporated into the Cameca LEAP 4000X enabling substantially improved performance for a wide variety of real-world materials including metals, semiconductors, and dielectrics. By utilizing laser mediated thermal pulsing with a diffraction-limited laser spot, the time-of-departure spread for field-evaporated ions is minimized resulting in high mass resolving power. The small spot also means that a minimal amount of heat is required to achieve the desired temperature pulse at the specimen apex leading to rapid cooling of the sample, higher spatial resolution, compositional accuracy, and enhanced analysis yield.The materials science fields of ceramics and oxides are currently being opened up to APT. A partial list of insulating materials that have recently been evaluated using laser-pulsed APT includes Al2O3 [1, 2], SiO2 [2,3], ZnO , CeO2 , MgO , InO , and FeO . The LEAP 4000X holds promise for improving both data quality and analysis yield for semiconductor applications and structures containing dielectric layers and/or complex 3D structures. Improved quantification of dopant ions and other dilute species is realized because of a combination of higher mass resolving power, smaller background contributions, and removal of overlap of neighboring mass peaks and tails. Real-time data quality metrics and features that detect and automatically respond to ion-evaporation excursions have been shown to reduce specimen fracture. This is especially important when attempting to analyze through dielectric interfaces. When coupled with advances in sample preparation, the LEAP’s wide field-of-view and improved yield on fragile samples, analysis of complex structures like single-bit modern transistors is possible .  E.A. Marquis, N.A. Yahya, D.J. Larson, M.K. Miller, R.I. Todd, Materials Today 13(10), 42 (2010). D.J. Larson, et al., Microscopy and Microanalysis 14, 1254 (2008). E. Talbot, R. Larde, F. Gourbilleau, C. Dufour, P. Pareige, European Physical Letters 87, 26004 (2009). Y.M. Chen, T. Ohkubo, K. Hono, Ultramicroscopy 111, 562 (2011). F. Li, T. Ohkubo, Y.M. Chen, M. Kodzuka, K. Hono, Ultramicroscopy 111, 589 (2011). D.J. Payne, E.A. Marquis, Chemistry of Materials 23, 1085 (2011). M. Bachhav, R. Danoix, F. Danoix, B. Hannoyer, S. Ogale, F. Vurpillot, Ultramicroscopy 111, 584 (2011). D.J. Larson, et al., Microscopy and Microanalysis in press (2011).
9:00 PM - PP3.9
Atomistic Simulations of Atom Probe Tomography Tip Evolution.
Stefan Parviainen 1 2 , Steve Fitzgerald 3 , Flyura Djurabekova 1 2 , Kai Nordlund 1 2 Show Abstract
1 Department of Physics, University of Helsinki, Helsinki Finland, 2 , Helsinki Institute of Physics, Helsinki Finland, 3 , Culham Centre for Fusion Energy, Oxford United Kingdom
Atom Probe Tomography (APT) is one of the most accurate methods available today for determining the chemical composition of a specimen in three dimensions. Using current techniques it is in many cases possible to obtain a reconstructed image of a specimen with nanometer resolution. Recent advances such as pulsed laser heating and new specimen manufacturing techniques have enabled the study of many new materials using APT, making the technique increasingly popular.APT relies on the controlled field evaporation of ions from a sample specimen. However, to be able to create an accurate reconstruction of the sample the shape and strength of the local electric field above the specimen must be known with high accuracy. As this information is generally not known current reconstruction algorithms instead rely on several approximations, such as assuming a specific sample geometry and linear flight paths of evaporated ions, which can limit the reconstruction resolution and result in aberrations. In reality the sample geometry and the local electric field are constantly evolving as individual atoms are evaporated. Additionally, the presence of precipitates can significantly affect the surface evolution. To be able to overcome the limitations of the assumptions an increased understanding of the evolution of the sample is needed.We propose a new model for simulating the field evaporation occurring in APT on an atomistic level. The model includes dynamic changes to the sample geometry and local electric field and is based on previous work where we extended a code for classical Molecular Dynamics by including the effects of an applied external electric field. The resulting local field is obtained by solving Laplace's equation. We have further extended the code by including a Monte Carlo step to account for the probability of charged surface atoms to evaporate. This enables simulation of field evaporation at cryogenic temperatures. Because the value of the local electric field is known at every point in the simulation it is possible to calculate the flight trajectories of evaporated atoms with high precision.Comparison between trajectories obtained in simulations and those given by commonly used approximations show that local changes in the electric field can cause significant distortions in the reconstructed images. We also show that precipitates and the initial sample geometry significantly affect the quality of reconstructed images.
Frank Muecklich Saarland University
David Seidman Northwestern University
Yuich Ikuhara The University of Tokyo
Institute of Engineering Innovation
Paul Midgley University of Cambridge
Manfred Ruehle Max Planck Institute for Metals Research
PP6: Poster Session
Tuesday PM, November 29, 2011
Exhibition Hall C (Hynes)
Tuesday PM, November 29, 2011
Fairfax A (Sheraton)
9:30 AM - **PP4.1
Steve Pennycook 1 , A. Lupini 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
In scanning transmission electron microscopy (STEM), aberration correction allows a larger convergence angle to be used, which in turn allows an improvement in the 2-dimensional (2-D) resolution to be achieved. The larger angle also results in a reduced depth of field, which allows a 3-D image stack to be obtained by changing focus between frames and effectively recording a series of slices. The benefit of this imaging mode is that it can allow high lateral resolution and even sensitivity to single heavy atoms. Applications have included locating single Hf atoms in a gate dielectric, identifying single heavy metal catalyst atoms on an oxide support material, and locating nanopaticle labels inside cells. The main drawback of this technique is that the vertical resolution is significantly worse than the lateral resolution. For extended objects, the depth resolution is limited by the lateral extent of the object and is therefore usually worse than might be expected from the depth of field alone. Variants of this technique using an annular or an oversized aperture can allow an improvement in the vertical resolution for extended objects. One practical advantage of this technique relative to tilt-series tomography is that there is no need to tilt the sample, however, because the convergence angle, even in an aberration-corrected STEM is much lower than typical tilt-series ranges, this results in a significant missing cone of information in 3-D Fourier space. Obtaining tilt-series STEM at different tilt angles may provide one route to filling in this missing cone. Work supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy, at Oak Ridge National Laboratory.
10:00 AM - **PP4.2
Quantitative Scanning Transmission Electron Microscope (STEM) Tomography in an Aberration Corrected Environment.
Matthew Weyland 1 , J. Shih 2 3 , C. Dwyer 1 2 3 , B. Muddle 2 3 Show Abstract
1 Monash Centre for Electron Microscopy, Monash University, Melbourne, Victoria, Australia, 2 Department of Materials Engineering, Monash University, Melbourne, Victoria, Australia, 3 ARC Centre of Excellence in the Design of Light Metals, Monash University, Melbourne, Victoria, Australia
Electron tomography (ET) is now a well-established technique for the determination of 3D structure in materials at resolutions on the order of a few nanometres. In addition there are increasing numbers of examples applying quantitative analysis of volumetric ET data for correlation with materials properties. However, as soon as quantification becomes the goal additional challenges are faced in terms of experimental design, volumetric analysis and factoring errors. It is also the case that aberration corrected STEM instruments are being increasingly employed to carry out ET experiments. While these instruments offer many advantages, in terms of imaging resolution and stability, they also offer significant pitfalls for electron tomography. Results will be presented that investigate these two closely linked issues. An exploration will be made of the practical experimental design behind the application of ET in an aberration corrected environment. Considerations regarding sampling, as well systematic and random errors on quantification will be explored. Another factor that is changing is the specimens studied; in order to maximise acquired ET data the “needle” geometry specimen, which allows 360° rotation is currently regarded as optimal for sampling. Results will be presented on the optimal approach to the preparation of metal alloys into “needle” specimens, and several examples of what can be achieved will be presented.The results presented will concentrate on the application of these techniques to nano-sized precipitates in aluminium alloys. In particular the 2xxx series Al-Cu-x and Al-Cu-Li-x systems. The physical properties of these alloys have been directly related to the type, habit plane, size, morphology and distribution of these precipitates. Unfortunately the measurement of these inherently 3D properties is limited by their small size; leading to many 2D methods requiring assumptions regarding their shape factors. In addition there are many cases where properties are cannot be correlated with simple, 1st order characters (such as size, number density or volume fraction) but more difficult 2nd order characters (such as inter-planar spacing, end to end distances or interconnectedness). Clearly a truly 3D characterisation technique, such as quantitative electron tomography, will be key to unravelling such correlations.
10:30 AM - **PP4.3
The Present and Future of Atom-Scale Tomography.
Thomas Kelly 1 , Michael Miller 2 , Krishna Rajan 3 , Simon Ringer 4 , Albina Borisevich 2 Show Abstract
1 , Cameca Instruments, Inc., Madison, Wisconsin, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Dept. Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 4 Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, Australia
T.F. Kelly1, M.K. Miller2, K. Rajan3, S.P. Ringer4, A.Y. Borisevich21Cameca Instruments Inc., 5500 Nobel Drive, Madison, WI 53711 USA 2Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6136 USA3Iowa State University, 2240K Hoover Hall, Iowa State University, Ames, IA 50011-2300 USA4The University of Sydney, Sydney, NSW 2006, AustraliaThe logical conclusion of a march toward finer resolution for structural and compositional microscopies is an technique that reveals the precise three-dimensional position and identity of every atom in a “large” structure. Such a technique may be called atomic-scale tomography (AST). Major breakthroughs in microscopy, condensed matter physics, and materials science will occur when this information becomes readily available. In the ultimate expression of AST, vacancies and interstitial atoms would be resolved. If point defect content can be observed or inferred, then a host of dynamic materials processes may be studied with much greater success. At present, the primary techniques for atomic imaging are aberration-corrected (scanning) transmission electron microscopy ((S)TEM) and atom probe tomography (APT). Neither is able to achieve the necessary 3D atom-scale imaging. (S)TEM cannot determine the atomic species in 3D except is special cases and is limited in detection of light elements in many systems. Atom probe tomography (APT) does not achieve atom-scale resolution in all parts of an image and detects about 50% of the atoms.It is instructive to consider how AST might be achieved. By combining APT and (S)TEM, the limitations of each technique may be overcome and a robust synergy results. The Atom TOMography (ATOM) project [Miller and Kelly, 2010] has been proposed to achieve this true atom-scale imaging and quantitative analysis of materials in 3D. The ATOM concept is based on an integration of the materials characterization abilities of STEM/EELS and APT in a single instrument. The 3D data recorded could then be used to generate many other types of knowledge, such as the origins of mechanical, magnetic and electrical properties, through the use of appropriate computational modelling and simulation techniques. This presentation will provide an overview of the current state of APT and (S)TEM with attention paid to their strengths and limitations with regard to achieving AST. The requirements of AST will be reviewed and a plan for how to achieve this goal will be described. M.K. Miller and T.F. Kelly, “The Atom Tomography (ATOM) Concept,” Micro. Microanal. (2010) 16(S2) 1856. Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
11:30 AM - PP4.4
Atom Probe Study of Interfacial Abruptness on an N-Face GaN High Electron Mobility Transistor Structure.
Baishakhi Mazumder 1 , Man Hoi Wong 2 , Umesh Mishra 2 , James Speck 1 Show Abstract
1 Materials, UCSB, Santa Barbara, California, United States, 2 Electrical and Computer Engineering, UCSB, Santa Barbara, California, United States
N-face GaN-based high electron mobility transistors (HEMTs) have been proposed for future millimeter-wave GaN electronics. A simple N-face HEMT consists of GaN(channel)/AlN(back-barrier)/GaN(buffer) , where the 2-D electron gas with mobility of 1350 cm2/Vs is induced at the top GaN/AlN interface. The roughness and abruptness of GaN/AlN interfaces are therefore of interest, motivated in part by the large strain in AlN (2.4%), as these determine the performance of devices. Two advanced structural/chemical characterization techniques for detailed analyses at scales <100 nm are 3-D transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) are limited by a spatial resolution of 1.5 nm3 . However, atom probe tomography (APT) provides 3D maps of the chemical distribution with sub nanometer spatial resolution (<0.1nm) which is much higher than any existing technique . In this work, we apply APT technique to analyse a GaN/AlN HEMT structure. The samples were grown by plasma-assisted molecular beam epitaxy on free-standing N-face GaN substrates from Lumilog. The growth was carried out at 710 °C under Ga-rich conditions slightly above the boundary for droplet formation. The growth began with 140 nm of GaN to provide a smooth step-flow surface, followed by 2-nm of AlN and 200 nm of GaN. These samples were then subjected to the FIB tip processing and analysed in LEAP 3000X HR. The tip was cooled at 30K and kept under high vacuum (10-10 mbar). To achieve controlled field evaporation of the atoms from the tip surface, a picosecond laser having wavelength of 532 nm with a pulsing frequency 200 kHz is employed with laser energy of 0.02 nJ and evaporation rate of 2%. The 3D tomography image shows the nature of interfacial abruptness between AlN and GaN for the MBE conditions employed. The bottom interface is found to be more diffused than the top one. The 10-90% distances at the top and bottom interfaces are found to be 0.64 nm and 1.02 nm respectively. Thorough compositional analysis is done using isosurface concentration. The average concentration for Al and N is found to be 46.5± 1.01% and 51.3± 0.92% within the AlN layer. The diffuse interfaces are likely due to roughness or the Ga wetting layer during AlN growth. These results will therefore enable the optimization of growth conditions. This input is used to understand the nature of interfaces and the roughness measurement, thereby enabling optimization of growth conditions. TEM and APT are used in a complementary fashion. By changing the experimental condition the field evaporation behavior of this material is understood. M. H. Wong et al., IEEE Electron Device Lett. 29, 1101 (2008) O. Erson et al., Solid State Sciences. 9, 1088 (2007)  Kelly TF, Miller MK. Rev. Sci. Instrum.78,031101(2007)
11:45 AM - PP4.5
Atom-Probe Tomography with Green or Ultraviolet Lasers: A Comparative Study.
Yaron Amouyal 2 1 , David Seidman 1 Show Abstract
2 Materials Engineering, Technion-Israel Institute of Technology, Haifa Israel, 1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Recent developments in the technology of laser-pulsed local-electrode atom-probe (LEAP) tomography include a picosecond ultraviolet (UV) laser system having a 355 nm wavelength and both external and in-vacuum optics. This approach ensures focusing of the laser beam to a smaller spot diameter than has heretofore been obtained using a green (532 nm wavelength) picosecond laser. We compare the mass spectra acquired, using either green or UV laser-pulsing, from nickel-based superalloy specimens that were prepared either electrochemically or by lifting-out from bulk material using gallium ion-beam milling in a dual-beam focused-ion beam microscope. The utilization of picosecond UV laser pulsing yields improved mass spectra, which manifests itself in higher signal-to-noise ratios (SNRs) and mass-resolving power (m/Delta-m) in comparison to green laser-pulsing. We employ LEAP tomography to investigate the formation of disoriented defects in nickel-based superalloys, and demonstrate that UV laser-pulsing is the only way to obtain an adequate accuracy in compositional quantification, which was not obtained using green laser-pulsing. Furthermore, we show that using a green laser the quality of mass spectra collected from specimens that were lifted-out using Ga+ ion-milling is usually poorer than for electrochemically-sharpened specimens. Employing UV laser pulsing yields, however, improved mass spectra in comparison to green laser-pulsing even for ion-milled microtips.
12:00 PM - PP4.6
Dynamic Projection Functions in Atom Probe Tomography.
Daniel Haley 1 , George Smith 1 Show Abstract
1 Materials, Oxford University, Oxford United Kingdom
Atom probe tomography is one of the key techniques for atomic scale volume imaging, with near-atomic resolution in homogeneous materials. This technique is pivotal in the characterisation of a wide variety of advanced materials, such as semiconductor devices or high temperature and complex precipitate reinforced alloys. As a technique, atom probe plays a significant role in modern materials design. This is due to its capacity for characterisation of atomic processes, which are critical in determining structural changes in bulk media. Phenomena such as defect migration, clustering and fine-scale phase separation can be difficult to study simultaneously using beam imaging methods. In such multicomponent materials, atom probe tomography excels in both chemical and depth resolution metrics, but has significant problems with lateral resolution in inhomogeneous materials due to ion path distortions [1-3].The limitations in lateral resolution stem from the unknown projection function being followed by the ion flight path. This projection function is the result of evaporative processes constructing a dynamically changing shape for the emitter which undermines the assumptions built into modern reconstruction approaches. Inhomogeneous media will not obtain a steady-state shape, and thus will have a dynamically changing interface.Level set methods have been extensively studied for the solution of moving front problems and have been widely applied to various boundary problems, including multiphase flow, image segmentation and even snow avalanche computations . We discuss the use of the level-set method for the solution of the tip shape through time and the subsequent projection function in inhomogeneous media.Several simple cases are examined in two and three dimensions, such as spherical/disk precipitates and rod geometries, as well as such as multilayer materials. We further discuss the relationships between signed distance field evolution, the image-hump model and the boundary solution to the Poisson equation in the context of simulated geometrical evolution of atom probe tips.Such a coupled solution to the geometric evolution of tips will be pivotal in constructing quantitatively combined TEM and APT datasets, whereby both TEM tomographic and atom probe datasets can be simultaneously exploited to maintain dataset integrity. De Geuser, F.; Lefebvre, W. et al Surf. Interface Anal. 2007; 39: 268–272 Oberdorfer, C. & Schmitz, G. Micros. and Microan., 2010, In press Vurpillot, F.; Bostel, A. & Blavette, D., Ultramicr., 2001, 89, 137-144 Bove, E. Ciaia, B & Preziosi, L.,Meccanica, 2010, 45, 753–765
12:15 PM - PP4.7
Atom Probe Tomography Investigation of Modified Carbide Precipitation in a Martensitic Steels.
Frederic Danoix 1 , Raphaele Danoix 1 , Andre Grellier 2 , Denis Delagnes 3 Show Abstract
1 Groupe de Physique des Matériaux, Université de Rouen - CNRS, Saint Etienne du Rouvray France, 2 Groupe Recherche et Développement , Aubert & Duval, Les Ancizes France, 3 Ecole des Mines d’Albi, Université de Toulouse, INSA, UPS, Mines Albi, ISAE; Institut Clément Ader; , Albi France
Atom probe tomography and 3D field ion microscopy allow true 3D investigation of materials at the subnanometer scale, in some case allowing atomic resolution. It is particularly adapted to investigate the early stages of precipitation of nanoprecipitates, in particular nucleation mechanisms.In the particular case of a newly developed dual precipitation medium carbon martensitic steels, atom probe tomography reveals the heterogeneous nucleation of secondary hardening carbides on dislocations, as well as the homogeneous nucleation of intermetallic NiAl particles. When both types of precipitates are present simultaneously, the presence of the intermetallic phase affects the nucleation mechanism and the spatial distribution of the secondary hardening carbides, which is changed from heterogeneous on dislocations to heterogeneous on the intermetallic particles. The consequences of this modification are a significant improvement of ultimate tensile strength up to 2 GPa, as well as the UTS – impact toughness compromise.
12:30 PM - **PP4.8
Chemical Nanotomography of Biomineral Nanocomposites.
Derk Joester 1 Show Abstract
1 Materials Science, Northwestern University, Evanston, Illinois, United States
Biological organisms possess an unparalleled ability to control the structure and properties of mineralized tissues. They, for instance, guide formation of smoothly curving single crystals or self-sharpening teeth. In many biominerals, the mineral interacts with an organic matrix during formation. This matrix controls mineral morphology and polymorph, and is frequently occluded during mineralization. The outstanding fracture toughness, wear resistance, and other outstanding materials properties can be attributed to buried organic–inorganic interfaces in the resulting nano-composite. Analyzing and controlling such interfaces at the nanometer length scale is critical also in emerging organic electronic and photovoltaic hybrid materials. However, the structural and chemical complexity of buried organic–inorganic interfaces presents a challenge to state-of-the-art imaging techniques.
Herein, we show that pulsed-laser atom-probe tomography reveals chemical levels of hierarchy at unprecedented length scale in the ultrahard tooth biomineral of a marine mollusc, the chiton Chaetopleura apiculata. We further report on new insights into the chemical nanostructure of mammalian tooth enamel, in particular the existence of interphases and pathways of fluoride diffusion. We anticipate that the quantitative analysis and visualization of nanometer-scale interfaces by laser-pulsed atom-probe tomography will contribute greatly to our understanding not only of biominerals (such as bone, dentine and enamel), but also of synthetic organic–inorganic composites.
(1) L. Gordon, D. Joester, Nature 2011, 469, 194-197.
Tuesday PM, November 29, 2011
Fairfax A (Sheraton)
2:30 PM - PP5.1
The Ageing Behaviour of Nb-V Bearing Castrip® Steels at Higher Temperature.
Chen Zhu 1 , Lan Yao 1 , Kelvin Xie 1 , Julie Cairney 1 , Simon Ringer 1 Show Abstract
1 Australian Centre of Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales, Australia
Recently, the research interest of Castrip® steels eventually progressed from plain low-carbon-manganese steels to more complicated microalloyed steel, particularly with the use of niobium and vanadium. Ageing treatment at different temperatures can generally improve the strength and ductility of Castrip steels. This paper applied varies advanced characterization techniques, including High Resolution Transmission Electron Microscopy (HRTEM) and Atom Probe Tomography (APT) to reveal the niobium-vanadium containing clustering process during ageing at 750°C and 800°C for varies of period of time, the effect of which is believed to be the major contribution to the mechanical property improvement after ageing.The results demonstrated that peak hardness could be reached by ageing at higher temperature for significant shorter ageing time at the same temperature, the density and distribution of (Nb,V)C type precipitates determine the mechanical property improvement dominantly. At the same ageing temperature, as the ageing time increases, the size of precipitates/clusters doesn’t grow obviously, instead the density of Nb/V atoms in the precipitates/clusters increases.
2:45 PM - PP5.2
3D Atom-by-Atom Imaging of Semiconductor Nanomaterials and Interfaces.
Oussama Moutanabbir 1 , Dieter Isheim 2 , David Seidman 2 Show Abstract
1 , Max Planck Institute of Microstructure Physics, Halle Germany, 2 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Long before transmission-electron microscopy, scanning-tunneling microscopy, and atomic-force microscopy became popular atomic-resolution methods for analyzing materials, field-ion microscopy and atom-probe field-ion microscopy were utilized to image and chemically analyze the arrangements of atoms in metals [1-5]. This research focuses on pulsed laser-assisted field-evaporation, which expands the avenues of applications of atom-probe tomography (APT) from highly conductive materials to poor conductors or insulators, including semiconductors and biological materials [3-5]. More specifically, we will show that the use of an ultraviolet laser (355 nm wavelength) to assist the evaporation improves the spatial resolution, mass resolving-power, and signal-to-noise ratio in local-electrode atom-probe tomography . Several examples of 3-D atom-by-atom mapping of semiconductor nanomaterials and interfaces will be presented and methods for preparing APT specimens using dual-beam focused ion-beam (FIB) microscopy will be presented. Additionally, we will discuss a variety of atomic transport and interfacial phenomena in isotopically engineered nanostructures  and metal-catalyzed semiconductor nanowires  based on laser-assisted 3-D APT imaging and analysis. References: E. W. Müller, Journal of Applied Physics 27, 474 (1956).  E. W. Müller et al., Review of Scientific Instruments 39, 83 (1968). D. N. Seidman, Annual Review of Materials Research 37, 127 (2007). T. Kelly et al., Annual Review of Materials Research 37, 681 (2007).  T. Kelly and M.K. Miller, Review of Scientific Instruments 78, 031101 (2007). O. Moutanabbir et al., Applied Physics Letters 98, 013111(2011). O. Moutanabbir et al., Nano Today 4, 393 (2009). O. Moutanabbir et al., ACS Nano 5, 1313 (2011).
3:00 PM - PP5.3
An Atom-Probe Tomographic Study of Core-Shell and Core-Shell-Shell Nanoscale Precipitates in Al-Li-Sc and Al-Li-Sc-Yb Alloys.
Matthew Krug 1 2 , David Dunand 1 , David Seidman 1 Show Abstract
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 , General Electric Aviation, Airfoil Materials, Cincinnati, Ohio, United States
Two alloys, Al-2.9 Li-0.11 Sc atomic percent (Al-Li-Sc) and Al-6.3Li-0.07Sc-0.02Yb atomic percent (Al-Li-Sc-Yb), are aged for different durations at 325°C to produce strengthening, nanometer-radius precipitates that were analyzed using local-electrode atom probe (LEAP) tomography. Whereas Al-Li-Sc peak-aged at 325°C contains alpha-prime–Al3(Li,Sc) precipitates, due to the faster diffusion of Yb compared to Sc at this temperature, Al-Li-Sc-Yb peak-aged at 325°C contains core/shell alpha-prime-Al3(Li,Sc,Yb) precipitates with a Yb- and Li-rich core, and a Sc- and Li-rich shell. Peak-aged Al-Li-Sc-Yb was subsequently heat treated at 170°C to produce an additional hardening increment due to the precipitation of alpha-prime-Al3Li shells on some of the alpha-prime–Al3(Li,Sc,Yb) cores, resulting in precipitates with a complex core/shell/shell structure. Precipitate radii and spatial arrangements were measured employing LEAP tomography. This information was used as a direct input to dislocation dynamics simulations resulting in predictions of the alloys strengths, which were compared with experimentally-measured Vickers microhardness measurements. Thus, we evaluate the accuracy of macroscopic mechanical property predictions made from nanometer-scale measurements of precipitate size and spatial distributions. An empirical law for the superposition of Vickers microhardness contributions from Li in solid-solution and from alpha-prime–Al3(Li,Sc,Yb) was experimentally-determined. An empirical law from simulated data was similarly determined for the superposition of critical resolved shear stresses due to alpha-prime–Al3(Li,Sc,Yb) precipitates and δ′–Al3Li shells in doubly-aged Al-Li-Sc-Yb. Simulations of aged Al-Li-Sc over-predict the strength if a single dislocation is used, and under-predict the strength if instead a pair of dislocations (a super-dislocation) is considered. For super-dislocation simulations of Al-Li-Sc, between the peak-aged state, 8 h, and the strongly over aged state, 1536 h, the precipitate bypass mechanism is in transition from one of mainly shearing, to mainly Orowan looping, while the distance between the leading and trailing dislocations increases. Also for Al-Li-Sc, the over aged state simulations predict a near convergence of strengths for single dislocations and super-dislocations. For dislocation pairs in doubly-aged Al-Li-Sc-Yb, the measured and simulated strength values agree to within their uncertainties.
3:15 PM - PP5.4
Quantitative Composition 3D Profiling of Conjugated Quantum Dots by TOF-MEIS.
DaeWon Moon 1 , YoungJoon Cho 1 , HyunWoong Yoo 1 , Mauricio Sortica 2 , Pedro Grande 2 Show Abstract
1 Center for NanoBio Convergence, Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 Department of Physics, UFRGS, Porto Alegre Brazil
Quantum Dots are intensively studied for potential applications in variety of areas such as biomedical imaging, display materials, and thin film solar cells. However, it is still difficult to get quantitative composition 3D profiles of quantum dots regarding to the cores and shells. Furthermore, quantitative analysis of conjugated layers of quantum dots is still to be developed. Reliable quantitative composition 3D profiling techniques of conjugated quantum dots are essential for practical applications of quantum dots for various areas.We have developed a time-of-flight medium energy ion scattering spectroscopy (TOF-MEIS) and a software PowerMeis that can determine quantitative composition 3D profiling of quantum dots with sub-nm depth resolution for detailed characterization of cores, shells, and its conjugate layers. 4 mL of CdSe/ZnS QD dispersed in toluene (emitting at 528nm with 30 nm FWHM, 2.5 mg/mL) was mixed with perfluorodecalin liquid (PFD, 4 mL) containing 50 L of 1H,1H,2H,2H-perfluorodecanethiol (PFDT)for ligand-exchange. After mixing of the two-phase solution at nitrogen atmosphere for 5 days at 40°C, the CdSe/ZnS QDs were partitioned into the PFD phase. The CdSe/ZnS QD in PFD solution was then washed three times with methanol. Next, QD solution was dried and measured on top of ATR window with a FT-IR spectrometer to confirm ligand exchange. TOF-MEIS spectra for ~ 3 nm CdSe/ZnS with a conjugated layer of PFDT was obtained with 70 keV He+ ions at 90o scattering angle. Simulations by PowerMEIS could determine that the CdSe core and ZnS shell composition is 0.73:0.27 and 0.55:0.45, respectively and the core radius is 1.4 nm and the thickness of shell is 0.6 nm. Regarding to the conjugated layer, the amount of F atoms per QD can be absolutely determined so that the number of PFDT molecules per QD was estimated to be ~950.
3:30 PM - PP5.5
Three-Dimensional Confocal Imaging of the Stick/Slip Mechanisms of Sliding of Model Rough Surfaces.
Demet Tatar 1 , Michael Aziz 1 , Frans Spaepen 1 Show Abstract
1 Applied Phsics, Harvard University, Cambridge, Massachusetts, United States
When two rough surfaces slide, the contact between their surfaces occurs by the touching of their asperities. In order to understand the friction, wear and contact fatigue properties, it is necessary to determine the evolution of this contact area during shear. It is useful to divide the real contact area into slip and stick regions. This paper introduces a new experimental technique for imaging the contact area and its variation directly in real time by confocal microscopy. The surfaces are PDMS replicas of various sand papers. The concentration, size and lifetime of the slip/stick regions are classified as a function of the normal load and relative velocity of the surfaces.
3:45 PM - PP5.6
Mechanical Properties and Structure in Precipitated Colloidal Silica.
Miao Wang 1 , Marcel Roth 1 , Guenter K. Auernhammer 1 Show Abstract
1 , MPI for polymer research, Mainz Germany
In colloidal systems, changes in structure and interaction potential between the colloids alter their mechanical properties. The correlation between structure and mechanics is investigated. Combined measurements using confocal microscopy and (piezo-) rheometry are applied for the simultaneous test of interior 3D-structure and rheology of the inorganic precipitated silica-gel. The amorphous silica-particle after the fragmentation of the gel is widely applied as nontoxic filler in paints, cosmetics and polymers. The gelation is in-situ observed by confocal microscopy, so that the growth of silica-particle and formation of gel can be directly investigated. Additionally, this process is also studied by a piezo-rheometer. The later allows determining the dynamic mechanical properties for samples of less than 100 µm thickness. The applied deformation lies typically below 1.0e-3 (absolute deformation smaller than 100 nm). By comparing with results from classical rheometer measurements (on thick samples and with higher deformation amplitude), the influence of measurement method on the gelation is discussed.
4:30 PM - **PP5.7
Segmentation and Tomography: Steps towards Combining Both into a Single Algorithm.
Marc De Graef 1 Show Abstract
1 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Segmentation, the separation of a data set into disjoint regions, is a fundamental problem in many areas of science. Traditionally, segmentation is carried out on 2-D images, and involves grouping together similar pixels based on an appropriate similarity criterion. Many techniques are currently available, usually separated into two categories, depending on their output: region growing, statistical segmentation, and watershed techniques produce a label field, in which each region of the image receives a different label, whereas graph cuts, active contours, and anisotropic diffusion algorithms produce the boundaries between those regions. Over the years it has become clear that there is probably no "one-size-fits-all" solution to the general segmentation problem. All of the aforementioned approaches can, in principle, be applied to 3-D "images" as well, so their usefulness in the segmentation of tomographic data sets needs to be evaluated. In this contribution, we will first define the tomographic segmentation problem, both for x-ray and electron tomography, and then we will introduce the concept of "prior knowledge," i.e., any kind of information that can be used to improve either the tomographic reconstruction, the segmentation, or both. We will give examples of the use of statistical segmentation algorithms for the segmentation of x-ray tomograms, and explain how one can introduce prior knowledge into the reconstruction process, leading to "discrete tomography." Then we will introduce vector field electron tomography, a recent technique to determine, in 3-D, either the magnetic induction or the magnetic vector potential field inside and surrounding a magnetized nano-scale particle. We will show that vector field electron tomography will benefit from the direct inclusion of prior knowledge into thereconstruction algorithm, to the point where reconstruction and segmentation are carried out simultaneously. Then we will return to x-ray tomography, and explore how prior knowledge and segmentation may be included during the reconstruction process. We will conclude this presentation with a brief review of medical tomography, a field that has produced many advanced algorithms that may benefit the materials community as well. In particular, we will attempt to clarify the mathematical formalism for tomography as used in the signal processing community, and adapt it to the needs of our materials community.
5:00 PM - **PP5.8
Simulation and In Situ Measurement of Boundary Migration in Polycrystals in 3-D.
Chris Hefferan 2 , Frankie Li 2 , Anthony Rollett 1 , Jonathan Lind 2 , Ulrich Lienert 3 , Robert Suter 2 Show Abstract
2 Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 1 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Advanced Photon Source, Argonne National Laboratory, Chicago, Illinois, United States
Advances in three-dimensional materials science are reviewed with an emphasis on progress in characterization and evolution of microstructure during grain growth. Non-destructive analysis of the microstructure of a Ni specimen was characterized by high-energy x-ray diffraction microscopy (HEDM) that enabled boundary motion to be observed. Measurements were carried out at the Advanced Photon Source at Argonne National Laboratory at beamline 1-ID using a near-field high resolution imaging detector that senses the diffraction signal arising from an entire layer or cross-section of material as the sample is rotated in a planar, micro-focused 65keV x-ray beam. The reconstructions of the 3D images used a forward modeling technique that indexes the orientation of each point in the sample independently of all others. Five successive states were observed for anneals at 800°C in a Ni sample in the form of a wire approximately 1mm in diameter. A minority of grain boundaries exhibited motion whereas the majority remained stationary. The 5-parameter grain boundary character distribution is compared for the mobile versus stationary boundaries. Comparisons are made between the grain boundary motions and values for boundary energy obtained from either experiment or calculation, along with calculated values of mobility. The strongly non-uniform boundary motion points to the need for modification of the MacPherson-Srolovitz theory to account for anisotropy.
5:30 PM - PP5.9
Three-Dimensional Tomography of Dielectric Materials Using Electrostatic Force Microscopy.
Clement Riedel 1 , Richard Arinero 2 , Angel Alegria 1 , Juan Colmenero 1 , Juan Jose Saenz 3 Show Abstract
1 , Donostia International Physics Center, San Sebastian, Gipuzkoa, Spain, 2 , Institut d'Electronique du Sud, Montpellier France, 3 , Moving Light and Electron, Madrid Spain
Among existing fine-scale tomography techniques (3D atom-probe, electron, X-ray and optical tomography…), no one is able to provide electrical information of buried objects or trapped charges in dielectrics. Electrostatic Force Microscopy (EFM) may represent a solution to overcome this constraint. EFM allows characterizing electric and dielectric properties with tens nanometer spatial resolution. It has notably been used to observe single charge decay, measure dielectric constant of insulating thin layers and image polymer dynamics. Moreover, it has been recently predicted that EFM should be a good candidate for subsurface characterization[4,5]. The aim of this work is to present the opportunity to perform EFM tomography, i.e. to obtain quantitative dielectric 3D information or subsurface trapped charges imaging. Potential applications could include, for example, the understanding of degradation of MOS devices performance in the space environment. Indeed, on one hand ionizing effects may induce charge trapping and on the other hand heavy ions can introduce latent defect into gate oxide, of which it is important to know the distribution as a way to gain insight into the involved mechanisms. In this contribution, we will first give a brief and rigorous introduction about how to tune an AFM in order to measure electrostatic force and force gradient signals. We will then present a numerical study that demonstrates how to realize EFM tomography. Based on the Equivalent Charge Method, both force and force gradient between a buried object (or trapped charges) and the AFM tip are calculated. The main idea is then to scan the sample at different tip sample distances and obtain the position and charge value of the object using reconstruction algorithms. The quantitative analysis here presented is a first step toward tomography for samples presenting “dilute” point charges. Those results will be confirmed and validated by first experimental observations performed on reference samples. Lateral resolution, sensitivity (i.e. ability to detect an object), performance and limitations of EFM will be discussed and compared to other existing tomography techniques. 1 Schonenberger et al, Physical Review Letters 65, 3162 (1990).2 Riedel et al, Journal of Applied Physics 106, 024315 (2009).3 Riedel et al, Applied Physics Letters 96, 213110 (2010).4 Zhao et al, Nanotechnology 21, 225702 (2010).5 Riedel et al, Applied Physics Letters, Accepted for publication (2011).
5:45 PM - PP5.10
Neutron Tomography and Diffraction of Intact, Commercial Lithium-Ion Polymer Batteries.
Leslie Butler 1 , Kyungmin Ham 2 , Burkhard Schillinger 3 , Eberhard Lehmann 4 , Ping Liu 5 , John Vajo 5 Show Abstract
1 Chemistry, Louisiana State University, Baton Rouge, Louisiana, United States, 2 CAMD, Louisiana State University, Baton Rouge, Louisiana, United States, 3 Physik-Department E21, Technical Universität München, Garching Germany, 4 Neutron Imaging Group, Paul Scherrer Institut, Villigen Switzerland, 5 , HRL Laboratories, LLC, Malibu, California, United States
Imaging an intact, commercial battery at it cycles and wears is proved possible with neutron tomography. The wavelength range of imaging neutrons corresponds nicely with crystallographic dimensions of the electrochemically active species and the metal electrodes are relatively transparent. The time scale of charge/discharge cycling is well matched to dynamic tomography as performed with a golden ratio based projection angle ordering. The hydrogen content does create scatter which tends to blur internal structure. In this report, three neutron experiments will be described: 3D images of charged and discharged batteries were obtained with monochromatic neutrons at the FRM II reactor. 2D images (PSI) of fresh and worn batteries as a function of charge state may show a new wear pattern. In situ neutron diffraction (ORNL) of the intact battery provides more information about the concentrations of electrochemical species within the battery as a function of charge state and wear. The combination of 2D imaging, 3D imaging, and diffraction data yield show how neutron imaging can contribute to battery development and wear monitoring.
PP6: Poster Session
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - PP6.1
Three-Dimensional EBSD Analysis of YSZ, NiO-YSZ and Ni-Alloy.
Laxmikant Saraf 1 Show Abstract
1 EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States
Yttria-stabilized zirconia (YSZ), NiO-YSZ and Ni-alloy are frequently used in solid oxide fuel cells (SOFC) as electrolyte, anode, metal interconnects and seals. Two dimensional microstructure analyses of these materials can provide limited information regarding the pore space volume, triple phase boundary length, density and cracks formation. Surface microstructure analysis of these materials using electron backscatter diffraction (EBSD) has many advantages such as combining high resolution microstructure with imaging to provide site specific information for phase, chemistry and morphology. Successive sectioning of YSZ, NiO-YSZ and Ni-alloy at the intervals of 50-100 nm using a focused ion beam (FIB) followed by EBSD analysis on each slice provide an additional advantage to extend such a site specific microstructure analysis in the third dimension. Especially for SOFCs, the three dimensional EBSD reconstruction can provide a real-time pore-space volume connected with grain orientation data, a potentially crucial combination to interpret surface reactivity and fuel gas conversion ratios as oppose to available triple phase boundary length in SOFC. Here, the advantages of 3D EBSD are discussed in the context of its applications to SOFC community. Various 3D EBSD reconstructions from these materials will be presented in details to define structure property relationships in dynamic operating conditions.
9:00 PM - PP6.11
Tomography with a Lab-Based X-Ray Microscope at 50 nm.
Arno Merkle 1 , Jeff Gelb 1 , Luke Hunter 1 , Tiffany Fong 1 , Allen Gu 1 , Naomi Kotwal 1 , S. Lau 1 , Wenbing Yun 1 Show Abstract
1 , Xradia Inc., Pleasanton, California, United States
Complementary imaging and analysis techniques are most useful when the sample or region of interest remains intact and structurally preserved. In this regard, 3D x-ray microscopy (3D XRM) has emerged as a powerful method that provides the ability to obtain microstructural information over time from a range of materials under varying conditions and environments, without imposing impractical sample preparation restrictions.In addition to synchrotron and soft x-ray tomography, laboratory-based x-ray sources have recently been coupled with high resolution x-ray optics to acquire tomographic data sets with resolution down to 50 nm. This ability to non-destructively span the nanometer-to-micron length scales in three dimensions has opened up exciting avenues to explore relationships between material performance and microstructure, as a necessary step before a final, often destructive high-resolution analysis (atom-probe, FIB-SEM or TEM serial sectioning) in the materials laboratory.The evolution of three-dimensional microstructure on the same region of the same sample can rapidly benefit materials modeling and optimization, by avoiding having to extrapolate based on statistical sampling from a large number of like specimens. We present examples from such ‘4D’ studies in which external conditions were applied to interrogate and understand mechanisms that led to microstructural change.For correlation to high-resolution techniques, surveying samples via 3D XRM can be used to register locations for extraction in the FIB-SEM for either final TEM or atom-probe analysis, making each of these techniques more efficient as well as placing them in greater context of a multi-length scale material. Finally, phase contrast imaging in laboratory XRM has made it possible to interrogate unstained soft materials, for which many of the same advantages apply.Examples are presented from a range of sample types with complex multiscale microstructures, including lithium-ion battery materials, solid-oxide fuel cells, porous soft membrane materials, ceramics, and more.
9:00 PM - PP6.12
Combining X-Ray Diffraction Contrast Tomography and Vertex Dynamics Simulations: An Integrated Approach for the Investigation of Microstructure Evolution in Strontium Titanate.
Melanie Syha 1 , Wolfgang Rheinheimer 1 , Michael Baeurer 1 , Erik Lauridsen 2 , Wolfgang Ludwig 3 , Daniel Weygand 1 , Peter Gumbsch 1 4 Show Abstract
1 Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe Germany, 2 , Risø National Laboratory, Roskilde Denmark, 3 , European Synchrotron Radiation Facility, Grenoble France, 4 ^, Fraunhofer IWM, Freiburg Germany
Strontium titanate was found to show a growth behavior deviating from the classical Arrhenius law. The presented approach aims at discriminating the origin for this phenomenon combining 3D x-ray diffraction contrast tomography (DCT) annealing experiments and mesoscale grain growth simulations. Strontium titanate specimen were alternately exposed to ex-situ annealing and high energy X-ray DCT measurements allowing to monitor the microstructure at multiple stages during grain growth. In order to investigated the previously suggested temperature dependency of the interface properties of strontium titanate, the experiment was carried out for all of the identified temperature regimes, showing different growth dynamics.The reconstructed microstructures and the crystallographic information gathered by DCT have been used to investigate the connection between grain morphology and orientation dependent interface properties. These microstructures served as realistic reference structures for the vertex dynamics model, rendering systematic parameter studies on the inclination dependent interface properties possible. 3D evolving microstructures obtained from reconstruction and simulation respectively are presented in combination with detailed topological and crystallographical characterizations.
9:00 PM - PP6.15
X-Ray-Induced Water Vaporization.
Byung Mook Weon 1 , Ji San Lee 1 , Jung Ho Je 1 , Kamel Fezzaa 2 Show Abstract
1 X-ray Imaging Center, Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, GyungBuk, Korea (the Republic of), 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Sample stability and safety from radiation should be ensured when using high-brilliance radiation sources. We present quantitative evidence of X-ray-induced water vaporization: water is vaporized at a rate of 5.5 pL/s with the 1-angstrom-wavelength X-ray irradiation of ~0.1 photons per square angstrom; moreover, water vapor is reversibly condensed during pauses in irradiation. This phenomenon is attributed to surface tension reduction by ionization and would be universally important in biological imaging using high-brilliance, ionizing radiation sources.X-ray imaging at the nano- and microscale is of great interest for applications in physical and life sciences, including X-ray physics, materials science, biological imaging, environmental analysis, archaeology, paleontology, and heritage restoration, because it facilitates the nondestructive, direct visualization of internal structures or elements. The large penetration depth of X-ray photons allows relatively thick samples to be visible. However, radiation damage from the energy deposited into the sample by the X-ray photons used for imaging is inevitable. Radiation damage to living tissues by radiation ionization is not yet fully understood. In previous works, we put forward a possibility of water vaporization by surface tension reduction [1-3] based on a linear relationship of the surface tension to the vaporization enthalpy, but quantitative evidence was lacking.Here, we provide quantitative evidence of X-ray-induced water vaporization using high-speed phase-contrast X-ray imaging. This effect can be fully recovered by a sufficient pause in the irradiation. This finding may explain why bubbles within biological samples are generated and/or expanded by high-brilliance X-ray photons, which has been a critical problem in X-ray biological imaging. Ionization-induced vaporization, which is attributed to a surface tension reduction, can be a significant source of vapor generation, which may be a possible cause of sample deterioration. High-brilliance X-rays can modify material properties, including surface tension and viscosity . The finding is important in supporting sample stability and safety from radiation damage with high-brilliance X-ray sources. This result is of significance in carrying out X-ray experiments for high-resolution analysis of small confined water or living tissues. Ionization-induced vaporization will be universally important in biological imaging when using high-brilliance, ionizing radiation sources besides X-ray sources.B. M. Weon et al., Phys. Rev. Lett. 100, 217403 (2008).B. M. Weon et al., Appl. Phys. Lett. 92, 104101 (2008).B. M. Weon and J. H. Je, Appl. Phys. Lett. 93, 244105 (2008).B. M. Weon et al., Phys. Rev. Lett. (2011), in press.
9:00 PM - PP6.16
Microstructural Characterization of Dry Snow Metamorphism Using X-Ray Computed Micro-Tomography and Scanning Electron Microscopy.
Ian Baker 1 , Si Chen 2 Show Abstract
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, 2 X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
The microstructural changes of dry snow, in which no free water is present, as it undergoes metamorphism, was studied using a combination of an X-ray computed microtomograph (micro-CT) and a scanning electron microscope (SEM). Fresh snow was collected during snowfalls, sealed, and stored in temperature-controlled cold rooms between periodic observations. Time series three-dimensional images were acquired using the micro-CT to examine the microstructural changes of snow aggregates and individual snowflakes. For new snow, which has a very high porosity, mass transport through vapor phase is the dominant mechanism of snow metamorphism. This is driven by differences in surface curvature, and is significantly accelerated by a temperature gradient. The evolution of structural parameters, including relative density, specific surface area (SSA), structure thickness (Sr.Th), structure model index (SMI), and degree of anisotropy (DA) was monitored using the micro CT throughout the experiments. The final microstructures were examined using the SEM. Research supported by U.S. Army Research Office Contracts 51065-EV and 53317-EV-CF.
9:00 PM - PP6.18
X-Ray and SEM Tomography of Extremely High Surface Area Nanostructured Hollow Fiber Membranes.
Amy Grano 1 , Franchessa Sayler 1 , Keana Graves 1 , Brian Patterson 3 , Jan-Henrik Smatt 2 , Martin Bakker 1 Show Abstract
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Physical Chemistry, Abo Akademi University, Turku Finland
Hierarchically porous materials are of interest in a wide range of applications. If the materials are electronic or ionic conductors such materials are of interest as electrodes for use in fuel cells. Using hierarchically porous silica as templates, we have demonstrated the formation of hierarchically porous metal oxides and metals. By control of the synthesis conditions we have produced partial replicas ca. 1 cubic centimeter in volume, in which two macroporous networks are separated by a nanoporous membrane. The macroporous network in the silica template is known to be bicontinuous, and our underlying model predicts that the second, induced, macroporous network should be similarly bi-continuous.X-ray tomography of the whole samples is consistent with the replication producing one bi-continuous macroporous network, and shows the existence of a second set of macropores. Unfortunately, the resolution is not sufficiently high to determine if this second set of macropores is bi-continuous. Accordingly we have been carrying out FIB/SEM serial tomography in which a FIB is used to remove successive layers of a sample, with SEM imaging carried out between each FIB pass. The sequence of SEM images is then processed to give a 3-D representation. The SEM resolution is sufficient to resolve the macropores and demonstrate the bi-continuous nature of the network within the volume being imaged. However, the limited volume accessible in a single SEM image has required that a statistically meaningful number of volumes be imaged to establish that the second macropore network is bi-continuous throughout the sample volume.
9:00 PM - PP6.3
Three-Dimensional Analyses and Microstructure Modeling of LSCF Cathodes.
Jochen Joos 1 , Moses Ender 1 , Thomas Carraro 2 , Andre Weber 1 , Ellen Ivers-Tiffee 1 3 Show Abstract
1 Institut für Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany, 2 Institut für Angewandte Mathematik (IAM), Universität Heidelberg, Heidelberg Germany, 3 DFG Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany
The performance and durability of a solid oxide fuel cell (SOFC) is strongly related to the electrode performance, which is related to composition and microstructure of the porous materials. Therefore it is essential to know the microstructure as accurate as possible in order to separate the influence of material composition and microstructure. In the last few years, many groups used focused ion beam (FIB) tomography for the detailed analyses and reconstruction of porous electrodes [1-2]. From such reconstructions, microstructure parameters as volume fractions, surface area and tortuosity can be calculated and used in 1D models (such as e.g. ) to predict the area specific resistance (ASR). Moreover, a 3D reconstruction obtained by FIB tomography can be used as a detailed model-geometry in 3D microstructure models .A 3D finite element method (FEM) model is presented, which allows the calculation of the ASR directly from reconstruction data. Such a model can help to understand and improve electrode performance. Therefore, appropriate image processing steps such as rendering were applied on the obtained reconstruction, resulting in a more realistic and highly detailed microstructure. All necessary steps from the image generation to the FEM mesh generation and simulation will be illustrated in this contribution. The use of such a detailed microstructure reconstruction as model geometry enables us to focus on the material parameters (and additionally on the processes occurring inside the electrode), considering the geometrical ones as accurate given data. J. R. Wilson, W. Kobsiriphat, R. Mendoza, H. Y. Chen, J. M. Hiller, D. J. Miller, K. Thornton, P. W. Voorhees, S. B. Adler, and S. A. Barnett, nature materials, 5 (7), p. 541 (2006). J. Joos, T. Carraro, A. Weber, and E. Ivers-Tiffée, J. Power Sources, 196, (17), p. 7302 (2010). S.B. Adler, J. A. Lane and B. C. H. Steele, J. Electrochem. Soc., 143 (11), p. 3554 (1996).
9:00 PM - PP6.5
Effect of Flash Annealing on the Microstructure of FeCuNbSiB Alloys.
Pradeep Konda Gokuldoss 1 , Pyuck-Pa Choi 1 , Dierk Raabe 1 , Giselher Herzer 2 Show Abstract
1 Microstructure Physics and Metal Forming, Max Planck Institute for Iron Research, Düsseldorf, North Rhein Westphalen, Germany, 2 Development Rapid Solidification Technology, Vacuumschmelze GmbH & Co. KG , Hanau Germany
Fe-Si-Nb-B-Cu model alloys have been studied for years because of their excellent soft magnetic properties. Such tailor made compositions synthesised by Rapid Solidification Processing (RSP) technique renders amorphous materials lacking in long range order. Upon annealing, Fe-Si nanocrystals nucleate from the amorphous matrix in a crystallization process controlled by solute concentrations and annealing conditions. The soft magnetic properties are determined by the subsequent growth of Fe-Si nanocrystals in the amorphous matrix. The process of Fe-Si nucleation is reported to be heterogeneous, where the nucleation sites are clusters of Cu atoms formed due to a positive enthalpy of mixing with other alloying elements. Thus annealing results in a complex microstructure of nanometre-sized Cu clusters surrounded by Fe-Si nanocrystallites decorating the amorphous matrix. To understand the corresponding soft magnetic properties of such a nanocomposite, high resolution tomographic techniques need to be applied for micro characterisation.In the present work an optimised composition of a Fe73.5Si15.5Nb3B7Cu1 melt spun alloy with near zero saturation magnetostriction in the nanocrystalline state was studied. The samples were annealed under a small tensile stress for a short duration of about 4s at temperatures between 500 – 700 °C by continuously transporting the ribbon through a furnace kept under nitrogen atmosphere. The samples were studied by atom probe tomography, transmission electron microscopy and X-ray Diffraction. Due to the short annealing time the annealing temperatures needed to achieve the nanocrystalline state are about 100 °C higher than for more conventional prolonged heat treatments in the order of an hour. Such a difference in heat treatment has an effect on the size and number density of Cu clusters, the expected nucleation sites for Fe-Si nanocrystals. Surprisingly, the crystallite sizes of the Fe-Si nanocrystals are well below 15 nm.
9:00 PM - PP6.6
FIB SEM Tomography for Nano-EHS Applications.