Voordrachten 2015

Vrijdag 18 december 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp: Are DTI reproducibility studies reproducible? A closer look.
Spreker: Pim Pullens, Department of Radiology, Antwerp University Hospital & University of Antwerp

There is more and more interest in testing reproducibility of DTI measures, which could lead to use of DTI measures as clinical biomarkers. Coefficient of variation (std/mean) is often used to assess reproducibility. However, it is not trivial to compare CVs from different studies, each with a different number of subjects. In this meta-analysis across DTI reproducibility studies, we test if CVs and a new method for testing agreement, Total Deviation Index, are equal among published FA reproducibility studies with an appropriate statistical test. Results show that although confidence intervals of FA show deviations because of analysis or scanner type, CVs are comparable. TDI shows that that 90% of the absolute differences in FA values in the splenium of the corpus callosum between all studies and subjects are smaller than 12.6%.

Vrijdag 11 december 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp: Subpixel mapping
Spreker: Akhter Muhammad Awais , Vision Lab, University of Antwerp

Subpixel mapping predicts the location of land cover classes within a pixel using the fraction images typically produced by the soft classification or the spectral unmixing algorithms. Prediction is based on spatial dependence theory, which assumes that land cover classes are spatially dependent, both between and within pixels. Under this assumption, SPM increases the spatial resolution of the resulting land cover maps by dividing each image pixel into multiple subpixels.

Vrijdag 11 december 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Investigation of plasticity mechanisms at interfaces in Ni using ex-situ and in-situ SEM and TEM nano-mechanical testing
Spreker: Vahid Samaeeaghmiyoni, EMAT, University of Antwerp

The goal of this work is to elucidate the fundamental plasticity mechanisms operating at interfaces such as grain boundaries (GBs) and twin boundaries (TBs) during fatigue tests in Ni. To reach this goal, in-situ SEM loading cycles have been performed on bi-crystal micropillars with a well-known orientation as revealed by EBSD. Careful characterizations of the nature and the distribution of deformation dislocations, the character and the local structure of the interface as well as the mechanisms controlling the interaction between these defects under cyclic loads were performed using ex-situ TEM techniques including Diffraction contrast imaging, HRTEM as well as nano-strain mapping in TEM. On the other hand, in-situ quantified TEM tensile tests were used in order to directly observe the plasticity mechanisms. In order to minimize the effect of FIB damage on the in-situ experiments, an original method combining twin jet electro-polishing and FIB was used to prepare the samples.

Vrijdag 4 december 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp: Fast inline X-ray inspection of fruit
Spreker: Eline Janssens, Vision Lab, University of Antwerp

Inline inspection of fruit allows differentiation in quality. Computed tomography is one of the possible inspection methods. To limit the cost and improve the speed of the inspection system, a design with a fixed source and flat panel detector is preferred . To overcome the resulting limited wedge artefacts, the fruit will rotate on the conveyor belt. For an inline inspection system, both the image quality and the throughput of the system are important. The throughput of a CT based inspection system depends on the speed of its image reconstruction algorithm. Due to the limited data, known fast reconstruction algorithms like filtered back projection (FBP) provide inadequate reconstructions, while iterative reconstructions yield adequate reconstructions but they are too slow. In this talk, improvement of these reconstructions by the use of the Neural Network hFBP is discussed. This method yields high quality images in a short reconstruction time.

Vrijdag 4 december 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Strain analysis in new generation FETs with the combination of precession electron diffraction and Raman spectroscopy
Spreker: Antonios Nanakoudis, EMAT, University of Antwerp

Strain is an important physical parameter which controls the mechanical and electrical properties of materials. Intel first introduced strain in order to enhance the carrier mobilities of its transistors back in 2003. Since then, strain engineering has been a preferred strategy by microelectronics industry for boosting the transport properties of transistors.
The ability to describe and monitor the induced strain and its distribution inside the device is of high importance and therefore many characterization techniques, like X-ray diffraction (XRD) and Raman scattering have been used for strain analysis. However, these techniques fail to follow the continuous shrink of transistor dimensions due to their limited spatial resolution. For this reason, transmission electron microscopy (TEM) is currently the only tool able to sufficiently map strain due to its high precision and resolution down to nanometer scale.
Many TEM techniques have been used for strain mapping with each of them exhibiting advantages and disadvantages. In this lecture, the combination of precession electron diffraction (PED) and the non-destructive oil-immersion Raman spectroscopy for strain analysis of sub-40nm fin-shaped field effect transistors (FinFETs) will be discussed.

Vrijdag 27 november 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp : Dataset Delusion
Spreker: Joachim Ganseman, Vision Lab, University of Antwerp

More is better, is often thought when it's about test data. Thus, every research community now and then sees an even bigger dataset appear, for experimental evaluation of solutions to the problems they study. When their size or nature inhibits thorough manual verification of their contents, those datasets are at risk of being adopted "as is", forming a shaky basis for future research. This talk will point out some of the pitfalls when dealing with large datasets of unclear origins, starting from an exemplar case from the domain of Music Genre Recognition. The repercussions still echoing today, this case has prompted other investigations into the effect of faulty test data on figures of merit reported in recently published research.

Vrijdag 20 november 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp: Morphometric data fusion for early detection of Alzheimer's disease
Spreker: Diana Lorena Giraldo Franco, Computer Imaging and Medical Applications Laboratory - CIM@LAB' in Universidad Nacional de Colombia

Morphometry based methods allow the detection of subtle anatomical differences in the Magnetic Resonance Images (MRI) between healthy subjects and Alzheimer's Disease (AD) patients. This work presents an automatic method to classify between groups by comparing regions of interest that were extracted from brain models which capture the morphological and neuropsychological information.

Vrijdag 20 november 2015, 11.30 u., Lokaal U.244 (Campus Groenenborger)

Voordracht georganiseerd door EMAT en Nano Center of Excellence

Onderwerp: Spectroscopy and imaging of electronic and structural reconstructions at oxide interfaces
Spreker: Nicolas Gauquelin, EMAT, University of Antwerp

The study of novel physical properties appearing when two oxide materials are interfaced has become one of the major fields of research in solid state physics over the last decade. For example, the discovery of the formation of a conductive layer right at the interface region between 2 insulators (for example LaAlO3 and SrTiO3); the so-called two-dimensional electron gas (2DEG). I will present recent results aiming at understanding how to visualize and understand the effect of structural distortions (in the system LSMO/(STO)/NGO, electronic reconstruction and band bending (in LAO/STO, LAO/BTO and LAO/CTO) at the atomic scale. Their influence on physical properties will be discussed as well. I will finish by presenting some results on how a superconductor can be fully engineered through layer by layer deposition (SCCO/BCO).

Vrijdag 13 november 2015, 11.30 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Carbon based composites and hybrid nanostructures investigated by advanced transmission electron microscopy
Spreker: Mert Kurttepeli, EMAT, University of Antwerp

This talk will focus on the structural characterization of carbon based composites and hybrid nanostructures performed by transmission electron microscopy. The talk is divided into two main parts. The first part is devoted to the systematic investigation of structures obtained using a method based on a templated approach which aims to produce large areas of highly ordered, isolated, well-aligned and long carbon nanotube bundles. The second part focuses on the structural characterization of carbon nanosheets and carbon nanotubes which are used as templates for the synthesis of various metal/metal oxides for different materials applications. Combining conventional and advanced transmission electron microscopy techniques, the structural transitions and the interaction between coatings/templates and carbonaceous species will be revealed.

Vrijdag 6 november 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Three-dimensional characterization of atomic clusters, nanoparticles and their assemblies by advanced Transmission Electron Microscopy
Spreker: Thomas Altantzis, EMAT, University of Antwerp

Atomic clusters, nanoparticles and their assemblies have attracted enormous attention from the scientific community during the last years, thanks to their unique properties and numerous applications in a plethora of scientific fields. It has been proven experimentally that the structure of such nanomaterials is inseparably connected to their characteristic properties. Therefore, in order to deeply understand the structure-to-property relationship, a detailed structural characterization by Transmission Electron Microscopy (TEM) is of utmost importance. However, one should never forget that TEM images correspond to 2D projections of a 3D object and very often such images cannot be used for a detailed structural and morphological characterization. In order to obtain more reliable information, a 3D characterization should be performed by the use of electron tomography. Since the turn of the century, the technique has been used to investigate the 3D structure of materials at the nanometer scale and below. In our work, different electron microscopy techniques in combination with tomography were used to characterize different nanostructures such as, silver atomic clusters confined in zeolites, monometallic, core-shell and asymmetric nanoparticles as well as assemblies of spherical and non-spherical nanoparticles.

Vrijdag 30 oktober 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Human body modeling
Spreker: Femke Danckaers, Vision Lab, University of Antwerp

The human body appears in many shapes and sizes. It is important for ergonomic products to have an accurate fit to ensure an optimal comfort. By building a statistical 3D shape model of the body, representing average shape and the variability inside the population, there is much more information available for the product developer. We want to build a statistical shape model based on the exterior of the body. Both pose and shape will be fully adjustable in this virtual mannequin. Therefore, it will be useful for product developers to deliver better, more comfortable, semi-personalized designs.

Vrijdag 30 oktober 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Electron diffraction tomography for structure solution and refinement of polyanion cathode materials for Li-ion batteries
Spreker: Olesia Karakulina, EMAT, University of Antwerp

The crystal structure study of cathode materials for rechargeable Li-ion batteries is challenging and more common diffraction methods such as powder x-ray and neutron diffraction often cannot provide complete structure data, especially for charged an discharged samples, due to the necessary mixture with other battery components for charging and the inability of XRD to decently detect the light element Li.  We will show in this lecture that electron diffraction tomography (EDT), based on taking electron diffraction patterns of crystals over a large tilting range, allows to perform ab initio structure solution of a single nm-sized crystal of such materials and can detect the position and occupancy of even the light elements as Li. Due to the low electron dose this technique is appropriate for the study of those Li- or Na-based battery materials that are inaccessible with other electron microscopy techniques.
As an example, the solution and refinement will be demonstrated of the crystal structures of pristine, half charged and fully charged Mn-substituted LiFePO4, known as one of the most used cathode materials in modern Li-ion rechargeable batteries. 

Maandag 26 oktober 2015, 16.00 u., auditorium N0.08 (Campus Drie Eiken)

Voordracht georganiseerd door TQC

Onderwerp: Attractive Bose gases: from quantum reflection to quantum-enhanced interferometry
Spreker: Prof.dr. Christoph Weiss, Joint Quantum Center, Durham University, UK

In a recent experiment at Durham University with attractively interacting bosons, we observed quantum reflection off an attractive barrier. The talk will start with modelling these results numerically. Attractively interacting Bosons in quasi-one-dimensional waveguides form weakly bound molecules, bright solitons. Bright solitons were discovered more than 160 years ago in a water channel: a water wave did not change its shape for many kilometres. Ultracold atoms with pairwise attractive interactions allow the creation of micro-versions of these bright solitons. These quantum bright solitons provide an ideal system to study quantum effects in the realm between macroscopic world our physical intuition is based on and the microscopic world of single atoms. The talk will show how many-particle quantum superpositions (Schodinger-cat states) generated from quantum bright solitons can be used for quantum-enhanced interferometry. While decoherence would destroy such quantum superpositions, it can also lead to new physics.

Vrijdag 23 oktober 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger

Voordracht georganiseerd door EMAT

Onderwerp: Tailored electron probes for selective detection of plasmonic excitations
Spreker / Speaker: Giulio Guzzinati, EMAT, University of Antwerp

Spectroscopical techniques in the TEM, while being highly relevant due to their unparalleled spatial resolution, do not yet allow to measure all the properties that are probed with the corresponding optical and X-ray based techniques.
We believe that the gap can be closed by manipulating the phase of the electron beam to produce special probes that selectively couple to desired properties of the sample.
In the study of plasmonic nanoparticles for instance, electron energy loss spectroscopic imaging (EELS-SI) allows to map the intensity of the electrical fields that characterise its optical response, but is completely blind to their direction, while light spectroscopy allows to probe the particles directionally by using linearly polarised light.
We will briefly introduce the general principles of inelastic electron scattering, and use them to show how so called "pi-beams" allow the selective probing of dipolar excitations in plasmonic nanostructures, similar to what is possible with polarised light. We conclude with an experimental proof of concept.

Vrijdag 16 oktober 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIE

Onderwerp: Dynamic intensity normalization in X-ray imaging
Spreker: Vincent Van Nieuwenhove, Vision Lab, University of Antwerp

In X-ray imaging, it is common practice to normalize the acquired projections using averaged flat fields. While conventional normalization, also known as flat field correction, is able to correct for spatial inhomogeneities, it fails to do so for time dependent variations. Unfortunately, these dynamic variations are often encountered in synchrotron facilities and complicate further data processing.   This talk will cover the basics of flat field correction and introduce a dynamic flat field correction algorithm which is able to deal with time dependent variations.

Vrijdag 16 oktober 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Quantitative electron tomography: measuring properties in 3D
Spreker: Bart Goris, EMAT, University of Antwerp

In the first part of this presentation, we investigate lattice strain in Au nanodecahedra using electron tomography. Although different electron tomography techniques enabled 3D characterizations of nanostructures at the atomic level, a reliable determination of lattice strain is not straightforward. We therefore propose a novel model-based approach from which atomic coordinates are measured.  This technique is then applied for the 3D reconstruction and characterization of so called ‘nanodechaedra’. Such particles consist of five segments bound by {111} twin boundaries, yielding a crystallographically forbidden morphology. In order to fill this gap, the atomic arrangement in each segment must contain significant displacements, resulting in large intrinsic strain fields that can now be visualized in 3D.
In the second part of this lecture, we have combined electron tomography with spatially resolved electron energy-loss spectroscopy. Using these methods, we are able to map the valency of the Ce ions in CeO2-x nanocrystals. Our three-dimensional results show a clear facet-dependent reduction shell at the surface of ceria nanoparticles. The novelty of this generic tomographic technique is that it allows a full three dimensional datacube to be reconstructed, containing a full electron energy-loss spectrum in each voxel.

Vrijdag 9 oktober 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Studying the micromechanics of martensitic phase transformations using high energy diffraction microscopy
Spreker: Aaron P. Stebner, Mechanical Engineering & Materials Science, Colorado School of Mines, USA

Modern theories of the micromechanics of martensitic phase transformations are nearly 80 years mature. Experiments to verify these theories at the micro-scale, however, are a relatively new success, as definitive ex-situ observations of these mechanisms are difficult. New non-destructive in-situ High-Energy Diffraction Microscopy (HEDM) techniques are being developed to address this gap. Nickel-Titanium and Iron-Palladium shape memory alloys, and also 301L Stainless Steel, have been used as model materials in the first experiments. In this presentation, we will review the new micromechanical insights arising from these experiments. We will conclude with a generalization of the capabilities created by these new experiments as they may be applied to other solid materials where the kinematics of microstructural interfaces play critical roles in defining material performances, such as functional ceramics and soft magnets.    

Dinsdag 29 september 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Tomographic Image Reconstruction Using Training Images
Sprekers: Per Christian Hansen, Technical University of Denmark, Lyngby, Denmark

Priors are essential for computing stable solutions to ill-posed problems, and they take many different forms.  Here we consider priors in the form of cross-section images of the object, and this information must be used in a fast, reliable, and computationally efficient manner. We describe an algorithmic framework for this: From a set of training images we use techniques from machine learning to form a dictionary that captures the de­sired features, and we then compute a recon­struction with a sparse representation in this dic­tionary. We describe how to stably compute the dictionary through a regularized non-nega­tive matrix factorization, and we study how this dictionary affects the reconstruction quality. Simulations show that for textural images our approach is superior to other methods used for limited-data problems.

Vrijdag 25 september 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Shape models in product development: design methods and case study
Spreker: Daniël Lacko, Vision Lab, University of Antwerp

Statistical shape models are frequently discussed in the field of computer-aided design. However, it is still unclear how these models should be incorporated in the design process. This talk will therefore provide an overview of a number of ways in which shape models can be employed for ergonomic product design. A case study of the design of a brain-computer interface headset will be presented, in which the headset is designed using two different methods: one-size-fits-all and by sizing system. Results show  that shape models have a significant impact on product design, and that it's not only feasible but even advisable to use 3D anthropometry for the design of devices that need to fit closely to the human head.

Dinsdag 22 september 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Effect of Demyelination on Diffusion Tensor Indices: a Monte Carlo Simulation Study” &  “Voxel-wise analysis of higher-order diffusion MRI data
Sprekers: Maximilian Pietsch & Jacques-Donald Tournier, Department of Biomedical Engineering, King's College London

Both Donald Tournier and Maximilian Pietsch are part of the Department of Biomedical Engineering at King's College London and working within the Department of Perinatal Imaging and Health, located within St Thomas's Hospital, London. They are developing exciting new methods to characterise tissue microstructure using diffusion MRI and will present their latest findings. Following their talks, there is a short visit planned to the Radiology dept. of the University of Antwerp. They currently have dismantled their MRI scanner for the purpose of a hardware upgrade and this is a nice opportunity to see what the scanner looks like from the inside.

Vrijdag  18 september 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: The quest for priors in Magnetic Image Reconstruction: introductory review with novel contribution
Spreker: Gabriel Ramos-Llordén, Vision Lab, University of Antwerp

Many attempts have been done so as to speed up MRI by acquired an under sampled dataset of measurements. Achieving a high quality reconstructed image in this under sampled scenarios has motivated the quest for suitable priors to ease this ill-posed reconstruction problem. In this talk, we will explain the main problems to confront in MRI reconstruction, remarking the important differences with other image processing modalities and reviewing the most successful prior applied until date, with special emphasis on sparsity-based methods. Finally, we will present a novel type of prior knowledge rooted on Bayesian theory which resembles sparse priors adding new advantages.

Vrijdag 3 juli 2015, 15.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Fast, whole brain Radial Diffusion Spectrum Imaging (RDSI) via Simultaneous Multi Slice Excitation
Spreker: Steven Baete, Center for Advanced Imaging Innovation and Research & Center for Biomedical Imaging, New York University School of Medicine, New York

Diffusion Spectrum Imaging (DSI) has become a powerful tool for non-invasive imaging of white matter brain architecture. Unfortunately, widespread clinical implementation has been hampered by long acquisition times. DSI approaches sampling q-space in a radial fashion have been shown to be more efficient and accurate. When combined with a multi-echo train, RDSI provides significant throughput improvements over conventional DSI. We demonstrate these new developments and introduce a further acceleration of multi-echo RDSI by extending this technique with Simultaneous Multi-Slice excitation. The combined acceleration allows for whole brain fully sampled RDSI in under 6 min.

Vrijdag 3 juli 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Small-scale plasticity mechanisms in crystalline and amorphous materials revealed by in-situ TEM nanomechanical testing
Spreker: Hosni Idrissi, EMAT, University of Antwerp

Recently, the development of a new generation of advanced instruments for in-situ TEM nanomechanical testing has allowed establishing a one-to-one relationship between load-displacement characteristics and stress-induced microstructure evolution in the transmission electron microscope. In the present work, it will be demonstrated that a step forward in the investigation of the small-scale plasticity mechanisms in crystalline and amorphous materials can be made by combining commercial [1] and in-house developed lab-on-chip [2] micro/nanomechanical testing techniques with advanced TEM techniques including high resolution aberration corrected TEM, Angstrom-beam-electron-diffraction as well as automated crystallographic orientation and phase mapping in TEM. These techniques have been used to reveal the fundamental plasticity mechanisms activated in nanocrystalline metallic thin films, metallic glass thin films and, more recently, the minerals of the Earth’s mantle.
[1] H. Idrissi, A. Kobler, B. Amin-Ahmadi, M. Coulombier, M. Galceran, J-P Raskin, S.Godet, C. Kübel, T. Pardoen, D. Schryvers. Appl. Phys. Lett. 104 (2014) 101903
[2] H. Idrissi, B. Wang, M.S. Colla, J.P. Raskin, D. Schryvers, T. Pardoen. Adv. Mater. 23 (2011) 2119

Vrijdag 12 juni 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Algorithms for parameter estimation in quantitative MRI
Spreker: Marcus Björk, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Uppsala University, Sweden

Through advanced signal processing, MRI can provide quantitative measures of tissue-specific physical properties.  The optimization problems solved in quantitative MRI are typically nonlinear, and require intelligent and application-specific algorithms to avoid suboptimal local minima. In this presentation, several methods for efficiently solving different parameter estimation problems in MRI, such as multi-component T2 relaxometry, and minimizing banding artifacts in bSSFP MRI due to field inhomogeneity, are presented. Finally, I will present some interesting problems for the future.

Dinsdag 9 juni 2015, 16.00 u., Lokaal N0.08 (Campus Drie Eiken)

Voordracht georganiseerd door EGM

Onderwerp : Dopant-Induced Exciton Trapping in Semiconducting Carbon Nanotubes:Spectroscopy and Dynamics
Spreker : Stephen K. Doorn, Center for Integrated Nanotechnologies, Los Alamos National Laboratory

The carbon nanotube surface presents a unique 1-dimensional world in which to probe the interplay between chemistry and exciton photophysics.
Understanding and control of nanotube surface chemistry is vital to tuning their photophysical properties, enabling separations, developing functional optical materials, and introducing new optical states.  This talk will present a broad range of photoluminescence (PL) imaging and spectroscopic studies at the single tube level that probe behaviors including how the nanotube surface defines exciton migration and interaction of excitons with adsorbed and covalently bound surface species.  Of particular interest is the introduction of new photoluminescent states generated via low-level covalent doping of carbon nanotubes.  Such states are red-shifted from the normal exciton emissive state and are gaining in interest due to their chemical stability and potential for significantly enhancing the nanotube PL quantum yields through conversion of dark excitons.  The nature of these optical states, however, is not yet well-understood.  PL imaging and spectroscopic studies of oxygen- and aryl diazonium-doped tubes at the single-tube and single-dopant site levels will be presented.  Dynamic and static emission behaviors will be discussed as the interaction of 1-D exciton behaviors and 0-D trap states introduced at the dopant sites.  PL spectroscopy of single doped tubes at cryogenic temperatures and dramatic increases in PL lifetimes indicate exciton localization at dopant sites.  Fine structure in emission spectra may also be used to identify the chemical functionality of the dopant sites.  Relevant to interest in these new emitting states as single photon emitters for quantum information processing, we also demonstrate an approach to stabilizing emission output while also introducing solitary dopant sites.  Finally, lifetime and photon correlation studies enabled by superconducting nanowire single-photon detectors will be presented.  Evolution of behaviors as a function of temperature will be discussed in the context of realizing room-temperature photon antibunching.

Vrijdag 29 mei 2015 , 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Well-aligned carbon nanotube bundles directly grown through a porous membrane
Spreker: Mert Kurttepeli, EMAT, University of Antwerp

Carbon nanotubes (CNTs) can be spun into fibers of very high length. However, the resulting materials exhibit significantly reduced strength when compared to individual CNTs. By developing a new procedure of CNTs growth, it is hereby aimed to overcome this problem by allowing the bundling of CNTs already during the synthesis. In this respect, well aligned CNT bundles were directly grown through a porous membrane by means of the catalytic chemical vapor deposition (CVD) technique. We carried out detailed transmission electron microscopy (TEM) characterization on the as-grown CNTs and their bundle formation. The results indicate the proof of principle of this new idea. Especially, electron tomography combined with energy dispersive X-ray (EDX) chemical analysis gives detailed information about the CNTs growth at the nanoscale. This newly developed CNT growth method has high potential to produce CNT bundles in one process that can also be scaled up for industrial applications.

Vrijdag  22 mei 2015,  16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Projection-based polygon estimation in X-ray computed tomography
Spreker: Andrei Dabravolski, Vision Lab, University of Antwerp

In X-ray computed tomography, the 3D structure of a scanned object can be reconstructed from a number of projection images of the object acquired from different directions. Conventional tomographic reconstruction algorithms represent the reconstructed volume on a voxel grid. Such representation is, however, not well suited for polyhedral objects arising in many industrial applications, since such objects are first voxelized during the reconstruction and then processed in order to obtain a polygon mesh representing the surface of the object. These transformations lead to loss of details and may induce artefacts that hinder posterior image processing.
In this talk, a new approach is presented in which a contour polygon of the object is directly estimated from the projection data. The approach is based on simulated projections of the polygon model and optimization of the vertex positions in the model with respect to the distance between the simulated and the original projection data (projection distance). The obtained results demonstrate the ability of the proposed algorithm to accurately represent the contour of the object even in case of noisy projection data.

Woensdag 13 mei 2015, 11.00 u., Lokaal U.241 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Multiple scattering assisted electron crystallography
Spreker: Christophe Koch, Carl-Zeiss Professor für Elektronen- und Ionenmikroskopie, University of Ulm

Multiple scattering of fast electrons on their way through matter is generally considered a nuisance in transmission electron microscopy, since it often prevents the resulting images from being directly interpretable, and also diffraction intensities are often not ammenable to  processing via the phasing techniques we know from X-ray crystallography.  While the quantitative simulation of multiple scattering has been known for a long time, the numerical inversion of this process has been an obstacle in the quantitative interpretation of most TEM data.  In this talk I will present our recent solution to the inversion of multiple scattering from series of HRTEM or diffraction patterns recorded at different beam tilts.

Vrijdag 8 mei 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: TEM on MOFs – Characterizing complex systems via chosen TEM techniques
Spreker: Christian Wiktor, EMAT, University of Antwerp & Ruhr-University of Bochum

Metal-organic frameworks (MOFs) consist of inorganic nodes, metal ions or metal ion oxo-clusters, connected by organic multitopic ligands, the so called linkers. Building blocks with a similar geometry yield isostructures and can be easily mixed in single crystal like structures while building blocks with a different geometry can yield new framework topologies. Due to the wide variety of available building blocks in terms of their geometry and chemical properties and their miscibility, there are almost limitless potential MOF structures. A variety of nanoparticles (NPs) can be embedded in their pore space can be used to embed. The resulting system is depending on the chosen loading process the NP precursor and the MOF itself. The tailorability of MOFs and their porosity renders them very interesting for applications like catalysis, gas storage and separation, sensors, and drug delivery. TEM is an ideal tool to investigate such complex systems on a local scale. However, since MOFs contain covalent bonds, light elements like carbon, and are porous they are usually very sensitive to the electron beam.
In this presentation two very different NP@MOF systems will be shown as two instructive extreme cases: In one, phosphotungstic acid NPs (and cetyltrimethylammoniumbromid) template the growth of the MOF resulting in a new structure. In the other NP@MOF sample the particles were predominantly arranged in 2D layers coinciding with 2D building faults in the MOF host. Both systems were investigated by electron diffraction to unveil the structural relations of the yielded NP@MOF structures to the parent MOF structures.
Finally it will be shown that quantitative elemental maps acquired in scanning transmission electron microscopy energy dispersive x-ray spectroscopy (STEM-EDX) can be acquired of beam sensitive MOFs. They were used to investigate the distribution of labeled and unlabeled linkers in mixed linker MOFs.

Vrijdag 24 april 2015, 16.00 u., Lokaal N1.08 (Campus Drize Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Atomic-resolution tomography of Au nanoparticles
Spreker : Jan De Beenhouwer, Vision Lab, University of Antwerp

Before a reconstruction algorithm can be applied to compute a 3D image from a set of 2D projections in electron tomography, alignment must first be carried out to correct for geometrical changes that may have occurred during the acquisition. However, in many cases, even a perfectly aligned set of projections will not allow to fully resolve the atomic structure in 3D due to both noise and the limited amount of projection data that is available. In this talk, a new reconstruction method will be presented that compensates for the lack of information, by using an 3D atomic model as prior knowledge within the reconstruction.

Vrijdag  24 april 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT 

Onderwerp: An introduction to MULTEM multislice program: A tool for TEM simulations
Spreker : Ivan Lobato, EMAT, University of Antwerp

Modern high-resolution transmission electron microscopy has significantly evolved into a powerful tool which is capable of reaching sub-Angstrom resolution making possible the precise and quantitative analysis of the collected experimental data. In this regard, the quantum mechanical nature of the electron-specimen interaction requires that the experimental data must be compared and complemented by numerical simulations. Therefore, the development of high precision simulation techniques implemented as friendly user software is a crucial step forward in this field.

In this lecture I will shortly introduce to you the newly developed EMAT user interface software for quantitative image simulation in electron microscopy so-called MULTEM. I will start by (1) describing the main available options, (2) how to set up the input parameters (Atomic positions, acceleration voltage, etc.) to perform simulation for multiple techniques like Conventional Transmission Electron Microscopy (CTEM), Electron Diffraction (ED), Annular Dark Field (ADF) TEM, Annular Bright Field Hollow Cone (ABF-HC), Precession Electron Diffraction (PED), Convergent Beam Electron Diffraction (CBED), Scanning Transmission Electron Microscopy (STEM) and imaging (I)STEM and (3) I will provide few examples in order to get yourself familiar with the current user interface. Finally I will talk about the new features in the forthcoming release.

Donderdag 23 april 2015, 11.00 u., Lokaal U.025 (Campus Groenenborger) 

Voordracht georganiseerd door EMAT 

Onderwerp: Growth, Assembly and Sensing Applications of Gold Nanoparticles
Spreker: Luis M. Liz-Marzán, BioNanoPlasmonics Laboratory, CIC biomaGUNE, Donostia-San Sebastián, Spain and Ikerbasque, Basque Foundation for Science, Bilbao, Spain

Abstract :
Nanoplasmonics can be defined as the science studying the manipulation of light using materials of size much smaller than the radiation wavelength. This is typically achieved using nanostructured metals, since they can very efficiently absorb and scatter light because of their ability to support coherent oscillations of free (conduction) electrons. Although the remarkable optical response of “finely divided” metals is well known since more than 150 years ago, the recent development of sophisticated characterization techniques and modeling methods has dramatically reactivated the field. Another extremely important pillar on which the development of nanoplasmonics has been based was the great advance in fabrication methods, which provide us with an exquisite control over the composition and morphology of nanostructured metals. Both lithography and solution chemistry have seen a tremendous increase in the control that can be achieved, to a degree that seemed impossible only a decade ago. In particular, Colloid Chemistry has the advantage of simplicity and larger scale production, while offering a number of parameters that can be used as a handle to direct not only nanoparticle morphology but also surface properties, assembly and subsequent processing. This talk will focus on recent advances in “colloidal nanoplasmonics”, highlighting promising directions in the various aspects involved, from synthesis to applications.
[1] Grzelczak, M.; Liz-Marzán, L. M. Langmuir 2013, 29, 4652−4663.

Vrijdag 17 april 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Controlling the radiation and lifetime of relativistic particles by shaping their wavepackets
Spreker : Dr. Ido Kaminer, Department of Physics, Massachusetts Institute of Technology, U.S.A.

We show that shaping the wavepackets of Dirac particles can alter their fundamental relativistic properties such as length contraction and time dilation, or even change the spectrum of the radiation they emit. In one work, we shape quantum particles as self-accelerating Dirac wavepackets and show how it extends their lifetime. This effect can be explained as a new kind of Aharonov-Bohm Effect that arises due to an effective potential induced by the interference of the self-accelerating wavepacket. In another work, we show that the quantum nature of a charged particle creates new phenomena in the Čerenkov radiation (which is the radiation emitted from a charged particle when it travels faster than the phase velocity of light in a medium). Specifically, with proper design of the particle wavepacket, we predict the traditional Čerenkov radiation angle splits into two distinctive cones of photonic shockwaves. More importantly, the spectral response reveals an upper frequency cutoff at which the photon emission rate is diverging – manifesting a new resonant light-matter interaction. Importantly, our findings are observable for electron beams with realistic parameters, suggesting applications such as monochromatic x-ray sources and new kinds of Čerenkov detectors.

Donderdag 9 april 2015, 16.00 u., Lokaal N0.08 (Campus Drie Eiken)

Voordracht georganiseerd door TQC

Onderwerp: Equation of state of composite bosons in the BCS-BEC crossover
Spreker: Prof. Luca Salasnich, Univ. Padua

I discuss very recent theoretical results [1,2] on the divergent zero-point energy of the D-dimensional superfluid Fermi gas in the BCS-BEC crossover. The divergent zero-point energy of the system is due to both fermionic single-particle excitations and bosonic collective excitations [1,2]. The regularization of the zero-point energy gives remarkable analytical results for composite bosons in two dimensions [1] and in three dimensions [2].
[1] L. Salasnich and F. Toigo, Phys. Rev. A 91, 011604(R) (2015).
[2] L. Salasnich and G. Bighin, Phys. Rev. A 91, 033610 (2015).

Vrijdag 3 april 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Perovskite Electrocatalysts for Energy Storage and Conversion
Spreker: Prof. Keith J. Stevenson, Skolkovo Institute of Science and Technology, Russia

Since the initial discovery of La0.8Sr0.2CoO3 as an active oxygen reduction (ORR) catalyst in 1970, numerous studies focused on the development of perovskite oxides as replacements for precious metals and their oxides as catalysts for both the ORR and the oxygen evolution reaction (OER) throughout the 1970’s and 80’s. The resurgence of research on perovskites over the past few years has been focused on reinterpreting many of these earlier studies in the hopes of identifying a unifying activity descriptor for the ORR and OER on the surface of perovskites. Recently, the idea that the eg filling of the transition metal in the AMO3 perovskite (where A is a lanthanide or alkali earth, and M is the transition metal) controls the electrocatalytic activity has gained significance credence. However, we have shown recently that amongst a series of perovskites with a nominal eg filling of   ̴1 (LaMO3, where M=Mn, Co, Ni, or Ni0.75Fe0.25), there exists significant differences in their activities for both the ORR and the OER, indicating that while eg filling may be an important initial guiding principle in the selection of perovskite catalysts, the mechanisms of the ORR and OER on perovskites with different transition metals is not universal and thus there are likely other more meaningful activity descriptors. A previously overlooked descriptor may be the role of mobile crystalline oxygen at the surface of perovskites, as this governs much of the activity of the same perovskite oxides at higher temperatures in solid oxide fuel cells (SOFCs). Recently, we demonstrated that by nanostructuring perovskites, we can significantly increase the diffusion rates of these oxygen ions through the crystal, leading to materials that can exploited for charge storage or for enhancing the reaction rates of the OER through vacancy mediated mechanisms. In this presentation, we will take a more direct look at the role of oxygen vacancies in the room temperature electrocatalysis of oxygen through chemical substitution of Sr2+ for La3+ in La1-xSrxCoO3-δ. Through the use of rotating disk electrochemistry, cyclic voltammetry, electron microscopy, nitrogen sorption, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis, we elucidate the differing reaction mechanisms of the ORR and OER on cobalt containing perovskites. Further, through precise control of oxygen vacancies, we demonstrate bifunctional catalysts with the lowest combined overpotential for the ORR and OER of any reported material.

Vrijdag 27 maart 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Cryo-EM techologies for studying macromolecular complexes
Spreker: Prof. Peter Peeters, Maastricht University

We generate lamellae of infected cells using cryo-FIB/SEM technology. The workflow starts on the CorrSight with live cell imaging of cell cultures on an EM carrier that can be used throughout the complete workflow in order to prevent loss of orientation and sample contamination or destruction. The instrument is a unique and dedicated light microscope for correlative microscopy including a fully integrated spinning disk system. Once a specific event or location has been identified by means of light microscopy and preserved by means of cryo-fixation, the vitrified sample can be re-examined on the CorrSight in a dedicated cryo-stage in order to precisely determine in 3D the position of interest. After transferring the sample to the Scios DualBeam, the identified region will thinned down to the appropriate thickness of about 200 nm without artifacts using the focused ion beam. The correlative software allows the transfer of all data from the CorrSight such as positions of interest and recorded images to the Scios DualBeam in order to know exactly where to prepare the lamella for subsequent high resolution cryo-TEM imaging. After thinning the grids will be loaded in the autoloader on the Arctica for high resolution cryo-tomography. The instrument is equipped with phase plate and high sensitive Falcon III direct electron detector for low-dose imaging, tomography software for automated low-dose tomography. The cryo-SPA, X-ray, and NMR data of the secretion system can then be docked into the images from vitreous sections or lamellae to construct a macromolecular map of the tubercle bacillus within the host cell. The broader objective is to gain insight into the structure and function of the mechanism for type VII secretion system-mediated translocation. This should lay the groundwork for the development of novel antibiotics and better vaccines.

Vrijdag20 maart   2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Iterative model-based reconstruction in computed tomography (CT) for fast fluid flow imaging
Spreker : Geert Van Eyndhoven, Vision Lab, University of Antwerp

Abstract: This talks starts with a basic introduction to computed tomography and iterative reconstruction methods. Next, a new iterative CT reconstruction algorithm for improved temporal/spatial resolution in the imaging of fluid flowing through solid matter is introduced. The study of fluid flow through solid matter by computed tomography (CT) imaging has a broad range of applications, ranging from petroleum extraction to scientific research on fluid dynamics. Current techniques are often limited by a low temporal/spatial resolution. The proposed algorithm exploits prior knowledge in two ways. Firstly, the time-varying object is assumed to consist of stationary (the solid matter) and dynamic regions (the fluid flow). Secondly, the attenuation of a particular voxel in the dynamic region is modeled by a piecewise constant function over time (i.e., the voxel consists of fluid or air). Experiments on simulation data and on a real neutron tomography dataset prove that the proposed approach can significantly increase the temporal resolution in comparison to conventional algorithms.

Vrijdag  20 maart 2015 , 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp : Local orbital angular momentum decomposition of electron waves in transmission electron microscopy
Spreker : Roeland Juchtmans, EMAT, University of Antwerp

Abstract: Analogously to the two dimensional Fourier expansion, any two dimensional function (e.g. the exit wave of an electron scattered on a sample) can be written as a sum of vortex Bessel beams. The corresponding coefficients, called OAM-coefficients, are heavily dependent on both the intensity and the phase distribution of the wave. Detecting these experimentally would tell us a great deal about a scattered electron's wave function and the scattering object.
In this lecture we will start by looking at some simple examples in order to get familiar with this way of looking at two dimensional (wave-)functions.  This is followed by a description of an experimental setup to measure these coefficients. Finally we will discuss possible applications ranging from detection of the chirality of crystals to the magnetic arrangement of atoms to visualizing weak phase objects.

Vrijdag 13 maart 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: The curse of dimensionality
Spreker: Rob Heylen, Vision Lab, University of Antwerp

The number of applications that require or generate high-dimensional data has grown exponentially in current years, and with the advent of big data, the internet of things, ultra-high resolution imagers, spectroscopers and cheap data storage and transfer, this trend will continue for some time. Unfortunately, not all data processing techniques can be trivially extended to any number of dimensions, as several exotic effects manifest themselves when the number of dimensions becomes very large. In this talk, we present several examples of this "curse of dimensionality", such as concentration of measure, sparseness, and hubness, and their consequences for several data processing algorithms. Furthermore, we show how one can exploit several of these observations to construct new applications in the field of hyperspectral image processing.

Vrijdag 13 maart 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Gaining dynamic control over electron vortices
Spreker / Speaker: Armand Béché, EMAT, University of Antwerp

The magnetic field created at the tip of a long ferromagnetic rod, approximating a magnetic monopole field, can create high purity and high intensity electron vortex beams with sub-ångström resolution. After carefully tuning the cross section of the rod by focused ion beam (FIB) milling, OAM values very close to one can be obtained. This is revealed by the measurement of the phase shift caused by the magnetic field close to the tip of the rod using holography in field-free conditions. The presence of an electron vortex was verified through a focal series experiment and by cutting the defocused probe with a sharp edge.
By applying a strong enough magnetic field along the needle length, it is possible to reverse its magnetic state, inversing the sense of the electron vortex. The interaction of such a tuneable electron beam with magnetic samples will be discussed in detail. Special attention is paid to the atomic resolution magnetic dependence of the EELS, linked to electron magnetic chiral dichroism (EMCD).

Vrijdag 6 maart 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Modeling blurring effects due to continuous gantry rotation: application to region of interest tomography
Spreker : Jeroen Cant, Vision Lab, University of Antwerp

Computed tomography (CT) is increasingly used to study dynamic processes, often referred to as 4D CT. The time resolution with which such processes can be studied strongly depends on the rotation speed of the gantry. Pushing the rotation speed to its limits, however, may result in blurred X-ray projections depending on the type of acquisition, which in turn leads to blurring in the reconstructed images. In this presentation, a technique is presented in which this angular blurring is modeled in the reconstruction algorithm to improve image quality and allow for faster gantry rotations.

Vrijdag 6 maart 2015 , 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp : Characterization of loaded mesoporous silica material by TEM
Spreker : Maria Meledina, EMAT, University of Antwerp

The discovery of a new family of mesoporous molecular sieves in the early 90s opened new horizons in the field of multifunctional materials. Ordered mesoporous silica with uniform pores organized into hexagonal, cubic or lamellar structures displays a huge surface area and is the ideal host-material for nanosized particles. Depending on the loaded guest, the obtained nanocomposite can be used in various application areas such as catalysis, drug delivery, optics or electronics. Most applications however require a detailed characterization of both the host and the guest material.

Electron microscopy techniques are ideal for an accurate characterization of the loaded mesoporous silica microstructure. In this work, a combination of imaging and spectroscopy approaches were used to study Hg@PMO, FeOx@COK-12 and TiOx@COK-12 materials. In this manner, the structure and morphology of both the host material and the guest-nanoparticles located inside the mesochanels were revealed.

Vrijdag  27 februari 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Multi-tissue spherical deconvolution for improved analysis of multi-shell diffusion MRI data
Spreker : Ben Jeurissen, Vision Lab, University of Antwerp

Spherical deconvolution of diffusion-weighted MRI data is a popular analysis method that allows extraction of white matter fibre orientation information in the living human brain, completely noninvasively. It can be used to track the long-range connections of the brain or serve as a tract-specific biomarker for neuronal loss in the study of neurodegenerative diseases. Recently, we proposed a new spherical deconvolution approach that models the presence of non-white matter tissue in voxels, which was previously unaccounted for, enabling unprecedented tractography and quantification of white matter. This presentation will introduce diffusion MRI and spherical deconvolution and give an overview of our latest developments with respect to multi-tissue spherical deconvolution and tissue segmentation.

Vrijdag  27 februari 201, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp : Towards high-precision estimation of 3D atomic positions: Simulation study using statistical experimental design
Spreker : Marcos Alania, EMAT, University of Antwerp

Nanostructures play key roles in a wide range of materials because of their unique physical and chemical properties. These properties are determined by their specific three-dimensional (3D) atomic structure. Therefore, development of new theoretical methods to determine the 3D atomic structure would allow a better understanding and control of their properties. Aberration-corrected scanning transmission electron microscopy (STEM) is considered as one of the most promising techniques to achieve atomic resolution in three dimensions at a very local scale due to the strong interaction of electrons with small volumes of matter. The ultimate goal is no longer the visual interpretability, but quantitative structure determination instead. Therefore, a quantitative measure will be proposed to evaluate the statistical precision with which the positions of the individual atomic positions can be estimated. Use will be made of high resolution STEM image simulations in which the unavoidable statistical nature of the observations is taken into account. The available expression has been used to evaluate a tomographic series of simulated images of gold nan-clusters in terms of the attainable precision with which the atomic positions can be estimated in 3D. Furthermore, this expression has been used to evaluate the precision as a function of tunable experimental settings including the electron dose, the number of projection images and the detector settings. One of the main challenges in this study has been the time required to simulate the images, which can lead to impractical computation times due to the time required to generate data for each position of the probe and for each image of the tomographic tilt series. Therefore, I will also present an analysis of these limitations and discuss up to which extent approximate simulation approaches are valid.

Vrijdag 20 februari 2015, 11.30 h, Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Unscrambling mixed elements of compound nanoparticles using quantitative scanning transmission electron microscopy
Spreker: Karel Van den Bos, EMAT, University of Antwerp

In today’s world, the field of nanotechnology is evolving rapidly, leading to more sophisticated products with improved properties. In this field, advanced material’s characterisation techniques are required since the exact atomic structure of materials determines their physical and chemical properties.
The Z-contrast of High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) creates images which are sensitive to both chemical and structural information at the atomic level. By combining statistical parameter estimation theory with image simulations quantitative numbers for the atom types and number of projected atoms in each atomic column can be extracted. This method involves the use of the so-called atomic column scattering cross-sections corresponding to the total intensity of scattered electrons in each atomic column. Precise knowledge about the number of atoms has shown its use to visualise the 3D atomic structure of monotype crystalline nanostructures. Applications in hetero-nanostructures are currently limited because of the lack of methods to quantitatively unscramble mixed elements. In order to help solving this problem, a model has been derived for predicting scattering cross-sections of mixed columns.
Finally, the use of scattering cross sections when quantifying Energy Dispersive X-Ray Spectroscopy (EDX) data will be explored. It will be shown that the combination of HAADF STEM with the chemical sensitivity of Energy Dispersive X-Ray Spectroscopy (EDX) may be of great help in order to unscramble mixed elements.

Vrijdag 13 februari 2015, 11.30 h, Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Novel approaches for structural and chemical characterization by electron tomography
Spreker: Daniele Zanaga, EMAT, University of Antwerp

Electron tomography is nowadays a standard for the structural and morphological characterization of nanostructures and nanoassemblies, yielding three-dimensional information of the morphology and inner structure, which is required to optimize the synthesis and to understand the connection between the structure and properties.
Despite of the advantages, the technique still suffers from a series of physical restrictions which limit the accuracy because of artifacts in the final reconstruction. Reduction of these artifacts and optimization of the reconstruction process can be carried out if valuable prior knowledge about the sample is available (DART, TVM). A new approach in the characterization of nanoparticles assemblies is adopted by exploiting the prior knowledge on the spherical shape of the particles constituting them. The reconstruction method developed enables a quantitative description of the nanoassemblies by directly providing coordinates and number of particles and demonstrates unprecedented results in the removal of missing wedge artifacts.
Combination of advanced reconstruction algorithms with chemical information obtainable from Energy Dispersive X-Ray Spectroscopy (EDX) is one of the most interesting new applications of electron tomography thanks to the recent introduction of the Super-X system. Quantification of EDX data is a crucial step in this combination and is nowadays carried out with the Cliff-Lorimer method. The ζ-factor method is a relatively new alternative to this method and offers different advantages. We will give an introduction of this new method and show how it is possible to use electron tomography to experimentally determine the ζ-factors for different elements in order to establish an accurate quantification method for EDX data.

Vrijdag 6 februari 2015, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Semi-supervised learning: an overview
Spreker: Jan-Pieter Jacobs, Vision Lab, University of Antwerp

Supervised machine learning algorithms are trained on pairs of inputs and outputs.
As such, they neglect a huge mount of data: all unlabelled data.
Semi-supervised learning algorithms incorporate unlabelled data together with supervised data to obtain more accurate results.
This lecture presents the problem setting, an overview of SSL approaches in the literature and remote sensing applications.

Vrijdag 6 februari 2015, 11.30 h, Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Utilizing electron microscopy for structural characterization of zeolites
Spreker: Tom Willhammar, EMAT, University of Antwerp

Zeolites are naturally occurring or synthetic crystalline porous aluminosilicates. They have applications in the chemical industry as catalysts, for separation of different molecules or removal of unwanted species from various systems.
The unique properties of zeolite materials are to a large extent determined by their pore structures both on atomic and mesoscopic lengthscales. In order to understand their properties, develop applications and design new synthesis routes it is hence of great importance to explore and determine their fine structures.
Electron microscopy provides powerful tools for these studies. Electrons interact much stronger with matter compared to X-rays. This makes it possible to collect single crystal diffraction data from very small crystals. This advantage in combination with the recently developed rotation electron diffraction (RED) for collection of 3D diffraction data is a great leap forward for studies of crystalline materials with small crystal size. The possibility of obtaining images with atomic resolution is a great tool for studies of materials containing disorder and defects. Electron tomography provides a perfect tool for studies of porosity in 3D and has developed into a crucial tool for studies of morphology and mesoporosity in zeolite crystals.
In this presentation several examples will be shown where the power of electron microscopy has been utilized in studies of novel zeolite materials.

Vrijdag 30 januari 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Monitoring of the SEI-Evolution of Uncoated and Carbon-Coated Si Nanoparticles by Transmission Electron Microscopy and Electrochemical Impedance Spectroscopy
Spreker: Kristof Van Havenbergh, EMAT, University of Antwerp

Silicon is probably the most promising anode material for Li-ion batteries because of its high specific capacity of 3572 mAh.g-1. Drawbacks are lithiation-induced volume changes and the continuous formation of a Solid Electrolyte Interphase (SEI) upon cycling of the electrode. Therefore, silicon-based anodes have not yet been able to convince on an industrial scale. A recent strategy is to focus on the influence of coatings and composite materials in order to control the volume changes and SEI-formation. To this end, the evolution of the SEI, as well as an applied carbon coating, on nanosilicon electrodes during the first electrochemical cycles is monitored. Two specific techniques are combined: Transmission Electron Microscopy (TEM) is used to study the surface evolution of the nanoparticles on a very local scale, whereas Electrochemical Impedance Spectroscopy (EIS) provides information on the electrode level. For the first time, a TEM-EELS fingerprint signal of carbonate structures from the SEI is discovered, which can be used to differentiate between SEI and a graphitic carbon matrix. Furthermore, the shielding effect of the carbon coating and the thickness evolution of the SEI is described. We conclude that EIS can be used as a fast tool to monitor SEI-formation.

Vrijdag 23 januari 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp : TEM study of disorder-order transformation in CoPt heat-treated in a magnetic field
Spreker : Hiroshi Akamine, EMAT, University of Antwerp

CoPt undergoes disorder-order transformation from a cubic disordered A1(FCC) phase to a tetragonal ordered L10 phase at 1045 K. The ordered L10 CoPt is expected as a promising material for magnetic devices due to its high uniaxial magnetocrystalline anisotropy. However, decrease in crystal symmetry in this transformation gives rise to three orientation variants, which largely decrease the total magnetocrystalline anisotropy. In order to obtain a single variant state, two-step heat-treatment in a magnetic field has been suggested, in which the first and second steps corresponds to nucleation and growth stages, respectively. However, detail microstructural evolution in this method has not been clarified.
In this study, pseudo-kinematical quantification of fraction of each variant in the magnetic field-induced preferential nucleation and statistical characterization of anti-phase boundaries (APBs) in HAADF-STEM images are performed in addition to conventional TEM observations. The former concluded that preferential nucleation is indeed introduced in a magnetic field, and the latter found that the width of APB in a stable ordered state is characterized by a few atomic columns.
As a separated work, characterization of twin boundaries in TiNi by HRTEM will be briefly given.

Vrijdag  16 januari 2015, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp : Characterization of Metal-Organic Framework materials by TEM: A Status Quo
Spreker : Stuart Turner, EMAT, University of Antwerp

Porous metal-organic framework materials have been studied intensively since their discovery in the late 1990s. Their high specific surface areas make them excellent candidates for applications in catalysis, sensing, hydrogen storage and gas separation. Many of these applications call for small nanoparticles or single atoms of foreign elements to be grafted or embedded into the MOF framework. However, accessing local information on the shape, size, and crystal structure of the MOF host together with information on the position, chemical nature and structure of the loaded materials by TEM remains challenging, due to the extremely sensitive nature of these materials.
In this contribution, an overview will be provided on recent TEM results obtained on empty and loaded MOF materials. These include nanosized MOFs, MOF thin films, metallic cluster-loaded MOFs and single-atom grafted material. The main techniques of use will be discussed, together with optimized experimental setups need to retrieve to the maximum amount of information from these delicate materials.

Dinsdag 6 januari 2015 , 16.00 u., Lokaal U.203, Campus Groenenborger

Voordracht georganiseerd door EDF

Onderwerp : What do we really know about Dark matter and Dark Energy?
Spreker : Dr. Charling Tao, CPPM/Marseille and THCA/Beijing

Cosmological observations are converging towards a Concordance Lambda Cold Dark matter (LCDM) model where the stuff we know and are made of, represents only around 5% of the density of energy in the Universe.  Most of Universe energy would be in the form of a cosmological constant (or Dark Energy?), and the rest is some mysterious Dark Matter.
I will review and question our present knowledge on Dark Matter and Dark Energy, and discuss  future projects that could shed some light on this  Dark Universe.