Voordrachten 2012

Vrijdag 7 december 2012, 11.30 u. , lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: ELNES: a powerful tool to investigate local boron environment and distribution in boron-doped nanocrystalline diamond
Spreker: Yinggang Lu, EMAT, University of Antwerp

Abstract: Boron-doped nanocrystalline diamond films grown under different conditions have been investigated using a combination of high resolution annular dark-field scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy. Using these tools, the local boron environment, distribution and concentration have been determined. The boron energy loss near edge structures reveals a distinct difference in coordination of the B dopants in "pristine" diamond areas and in defective regions. Tetrahedral and trigonal coordination of boron were determined in "pristine" and defective regions respectively. Quantitative B concentration maps evidence no preferential embedding of boron in grain boundaries, but there is preferential embedding at twin boundaries and incoherent defective regions. The energy shift between "pristine" and "defective" areas of the carbon σ* peak demonstrates that there is a bond length variation when different amounts of boron are incorporated into the crystal lattice.

Vrijdag 30 november 2012, 11.30 u. , lokaal X.009 (Campus Groenenborger)         

Voordracht georganiseerd door EMAT
Onderwerp: EM study of precipitates in as-cast and annealed Ni-Ti-Nb shape memory alloys and their influence on the martensitic transformation
Spreker: Hui Shi, EMAT, University of Antwerp

Abstract: Nb-rich precipitates in the matrix of as-cast and annealed Ni45.5Ti45.5Nb9 alloys are investigated by scanning and scanning transmission electron microscopy, including slice-and-view and geometric phase analysis (GPA). The Nb-rich bcc nano-precipitates in the as-cast alloy have a 10% lattice parameter difference with the B2 matrix and reveal compensating interface dislocations. The 3D reconstruction of the configuration of small Nb-rich precipitates in the annealed alloy reveals a wall-like distribution of precipitates, which may increase the thermal hysteresis of the material.

Vrijdag 23 november 2012, 11.30 u. , lokaal X.009 (Campus Groenenborger)         

Voordracht georganiseerd door EMAT
Onderwerp : Silver degradation in historical photographs: a TEM case study
Spreker : Eva Grieten, EMAT, University of Antwerp

Abstract: The development and evaluation of a new non-destructive conservation treatment is often based upon an in-depth study of a conservation treatment in relation to the specific degradation. In this project atmospheric plasma as a non-destructive technique for silver degradation in historical photographs is evaluated. Since a photographic emulsion consists of gelatine (soft matrix) and silver (hard particles), the traditional sample preparation methods cannot be applied. The first part of evaluating the conservation treatment is to fully characterize the degradation. By using diffraction patterns, images and elemental mapping the degradation can be identified with TEM.

Vrijdag 16 november 2012, 11.30 u. , lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Quantitative Electron Diffraction
Spreker: Senne Van Rompaey, EMAT, University of Antwerp

Abstract: Electron diffraction (ED) is often used to determine the unit cell and symmetry of an unknown material. Unfortunately, due to the strong interaction between the sample and the incoming electrons, the intensities of the diffracted beams lose their direct relationship with the structural parameters of the sample. The development of the precession ED and ED tomography partially solved this problem. Intensities measured with these techniques are useable for structure solution and refinement. Processing of this recorded ED data however, is of the utmost importance. During this lecture, different aspects of the data processing will be illustrated and discussed.

Vrijdag 9 november 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Incommensurately modulated scheelite-based structures CAEUxGD2-x(BO4)4 (x=0 to 2, B=W, Mo)
Spreker: Anne Bertha, EMAT, University of Antwerp

Abstract: The new materials of the series CaEuxGd2-x □ (BO4)4 (x=0 to 2) have a scheelite-based structure (ABO4). Scheelite-based compounds with B=W or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emitting-diode) and solid-state lasers. The goal of the current project is to determine the link between the cation distribution and luminescent properties. The structures can be periodically described in four (B=W) and five (B=Mo) dimensions. A model in superspacegroup I2/b(αβ0)00 was built for the first cases already, based on the experimental ED patterns and HAADF-STEM.

Donderdag 8 november 2012, 16 u., lokaal U024 (Campus Groenenborger)

Voordracht georganiseerd door TGM
Onderwerp: Variational study of Fermi surface deformations in Hubbard models
Spreker: Dr. J. Bünemann, Institut für Physik, DTU Cottbus (Germany)

Abstract: The study of correlation-induced superconductivity is a notoriously difficult many-particle problem. Despite 20 years of research on superconductivity in the cuprates, there still exists no microscopic theory that is able to describe these systems comprehensively. Even for the simplest theoretical realisation of the cuprates, a Hubbard model in two dimensions, we have not yet obtained a satisfactory understanding of its ground states. There is some evidence, from renormalisation group methods, that two dimensional Hubbard models can have superconducting ground states. Quantitatively, however, little is known about these states. In a recent work, we have therefore introduced a variational method which allows us to study in detail the superconducting as well as other potential ground-states, e.g., the so-called 'Pomeranchuk' or 'nematic' phases with a broken rotational symmetry [1]. In my presentation, I will give a thorough introduction into this new method and its results for the ground states of two-dimensional Hubbard models.
[1] J. Bünemann, T. Schickling, and F. Gebhard, Europhys. Lett. 98, 27006 (2012)

Vrijdag 26 oktober 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Uncertainty quantification for Predictive Simulations of a Scramjet Combustor
Spreker : Catherine Gorle, EMAT, University of Antwerp

Abstract: The presentation will give an overview of the overarching goal of the Stanford Predictive Science Academic Alliance Program, which is the quantification of the margin to unstart of the Hyshot II scramjet combustor. The concept of Uncertainty Quantification (UQ) in Computational Fluid Dynamics (CFD) will be introduced, mainly focusing on a methodology to quantify uncertainty in turbulence and turbulent mixing models.
The methodologies presented are the main focus of the research proposed for my Pegasus fellowship. They could be applied to a wide range of computational models and simulations, hence the goal of this presentation is to introduce the methods as a starting point for exploring new ideas and common research interests.

Donderdag 25 oktober 2012, 16 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door TQC
Onderwerp: Theory and experiments with quantum fl uids of light
Spreker: Iacopo Carusotton, INO-CNR BEC Center and Dipartimento di Fisica, Universita' di Trento ( Italy)

Abstract: A few years after the first observation of Bose-Einstein condensation, quantum gases of dressed photons in semiconductor microcavities (the so-called exciton-polaritons) are a powerful workbench for the study of phase transitions and many-body effects in a novel non-equilibrium context.
In this talk, I will first briefly review remarkable experiments investigating superfluid hydrodynamics effects in photon fluids hitting localized defects: depending on the flow speed, a wide range of behaviors have been observed, from superfluid flow, to the super-sonic Mach cone, to the nucleation of topological excitations such as solitons and vortices.
I will then illustrate recent theoretical studies in the direction of generating strongly correlated photon gases, from Tonks-Girardeau gases of impenetrable photons in one-dimension, to quantum Hall liquids in the presence of artificial magnetic fields.
Advantages and disadvantages of the different material platforms in view of generating and detecting strongly correlated gases will be reviewed, in particular laterally patterned microcavity and micropillar devices in the optical range, and circuit-QED devices in the microwave domain.

Vrijdag 19 oktober 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Magnetic nanoparticles and anticancer drug (Taxol) encapsulated in biodegradable and biocompatible polymers
Spreker : Maria Filippousi, EMAT, University of Antwerp

Abstract: Polymer-coated magnetic nanoparticles are materials with ample applications in biomedicine for the treatment of cancer and targeted drug delivery. An effective strategy towards a more site-specific drug delivery could be the entrapment of drug in polymeric carriers with magnetic properties. Thus, incorporation of magnetic nanoparticles (MNPs) in the core of drug-loaded polymeric micelles enables targeting to the desirable area by application of external magnetic field. In the present work multifunctional nanocarriers with multilayer core-shell architecture were prepared by coating superparamagnetic iron oxide nanoparticles encapsulated in the biodegradable and biocompatible triblock copolymers of poly(propylene succinate) (PPSu) and poly(ethylene glycol) (PEG). The drug loading efficiency and drug release properties were investigated using the hydrophobic anticancer drug Taxol. The anticancer hydrophobic drug was loaded into the mPEG–PPSu-mPEG embedded with magnetic nanoparticles. The structural and morphological characterization of the samples was performed by Powder X-Ray Diffraction (XRPD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques while the magnetic hysteresis loop was recorded at room temperature with Vibrating Sample Magnetometer (VSM). Moreover, HAADF-STEM images were acquired from the polymer embedded with MNPs and confirmed the encapsulation of the iron oxide nanoparticles in the polymer matrix. For quantitatively measurements of the nanoscale morphology of the soft materials embedded with magnetite we performed elemental mapping using EELS.

Vrijdag 12 oktober 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Recent developments on data mining the exit wave: residual aberrations, resolution and a new idea to determine the "weight" of the atom columns
Spreker : Amy Wang, EMAT, University of Antwerp

Abstract: As suggested by the title, the presentation consists of three parts. The first part is about determining the residual aberrations of the microscope in an experimentally reconstructed exit wave. In principle, the exit wave is reconstructed from a series of HRTEM images and is supposed to be free of microscope aberrations assuming the transfer function of the microscope is fully understood. However, due to instrumental instabilities, we cannot determine lens aberrations with sub-Å precision. Thus, there remain residual aberrations in the reconstructed exit wave which influences the quantification of structure parameters from the exit wave. In the second part, a method to determine the resolution in an object-independent way is introduced. In general, the resolution is determined related to the point spread function of the microscope where the atom is considered as a point object. However, as the resolution of the microscope enters the sub-Å regime which is of the same order as the width of an atom, the resolution is entangled with the information about the object. In the third part, a new method will be presented to determine the "weight" of the atom columns.

Vrijdag 5 oktober 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  EMAT
Onderwerp : Oxidation state mapping: from bulk to the atomic scale
Spreker: Haiyan Tan, EMAT, University of Antwerp

Abstract: Transition metals (TMs) in oxide materials are known to adopt many different oxidation states, leading to a wide range of chemical and physical properties. We present a thorough study of the link between EELS fine structure and oxidation state on a wide variety of bulk TM oxides. Combining this knowledge with the available atomic resolution in modern aberration corrected STEM instruments provides us with the possibility to extend oxidation state mapping to the atomic level. We demonstrated this exciting possibility on single crystals of Mn3O4 which are known for their ordered arrangement of Mn2+ and Mn3+ sites. This technique has also been applied to a super - lattice structure of SrVO3 and LaVO3 film to study the oxidation state of V at their interfaces. A fundamental asymmetry of V oxidation states was unambiguously revealed at atomic level between the LVO/SVO and SVO/LVO interfaces.

Vrijdag 28 september 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  EMAT
Onderwerp : Strain modified charge order at the oxide interface
Spreker : He Tian, EMAT, University of Antwerp

Abstract: Oxide materials show an amazing variety of electronic and ionic phenomena, exhibiting a wide range of phenomena such as magnetism, superconductivity, ionic conduction and ferroelectricity. In particular, oxide interfaces, offer the unique opportunity to control and enhance the effects by controlling the interaction between layers. One important goal is to tailor the amount of strain at the interface to tune the balance among the competing interactions and structural degrees of freedom available to oxides. Normally, strain is induced by an appropriately chosen substrate and is coherently maintained up to a critical thickness. Here, we use HAADF STEM in combination with mono EELS to investigate the chemical and magnetic properties of the Fe3O4/ZnO interface. A charge order of Fe 3+ and Fe 2+ are present at the monolayer of Fe3O4/ZnO interface, which are modified by strain due to lattice mismatch.

Vrijdag 28 september 2012, 17.15 u., lokaal U.203 (Campus Groenenborger)

Voordracht georganiseerd door  EDF
Onderwerp : the theory of Wilson lines and loops and properties of the loop space
Spreker : Tom Mertens, EDF, University of Antwerp

Donderdag 6 september 2012, 15 u., lokaal U.203 (Campus Groenenborger)

Voordracht georganiseerd door TGM
Onderwerp : Aspects of many-electron physics in graphene (I-III)
Spreker : Prof. Tapash Chakraborty, University of Manitoba, Canada and CMT, University of Antwerp

Abstract: In this lecture a brief background will be presented on the interacting electron gas in a magnetic field, the Laughlin state, and other materials relevant for graphene, and also the magnetic field effects on monolayer graphene.

Woensdag 5 september 2012, 16 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door  EGM
Onderwerp: Synthesis of Carbon Materials by Plasma Enhanced Chemical Super Critical Fluid Deposition / Highly Efficient Long-Lifetime Room Temperature Phosphorescence in Metal-free and Halogen-free Materials under Ambient Conditions
Spreker: Prof. Toshiyuki Watanabe, Tokyo University of Agriculture and Technology

Abstract:
Synthesis of Carbon Materials by Plasma Enhanced Chemical Super Critical Fluid Deposition
We will demonstrate a novel material synthesis process by plasma enhanced chemical supercritical fluid deposition (PE-CSCFD). Nano carbon materials and metal oxides were synthesized from carbon dioxide as a raw material by radio frequency plasma discharge under supercritical condition. This approach is not only unique method for carbon materials synthesis, but also promising candidate for new carbon dioxide fixation. The products were characterized by several techniques such as scanning electron microscopy, Raman spectroscopy, energy dispersive X-ray analyzer, X-ray photoelectron spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. These analyses reveal that only nano diamonds were synthesized with high growth rate from carbon dioxide.
Highly Efficient Long-Lifetime Room Temperature Phosphorescence in Metal-free and Halogen-free Materials under Ambient Conditions
Phosphorescence with a long lifetime (>1 s) can only be observed at low temperature from pure (metal-free and halogen-free) organic materials, because of the significant nonradiative deactivation pathway that occurs at room-temperature (RT). If pure organic materials with long-lifetime RT phosphorescence (LL-RTP) in air could be developed, they could be potentially utilized for a variety of applications. Here, we present pure organic host-guest materials with LL-RTP by minimizing the nonradiative deactivation pathway. The nonradiative deactivation pathway depended on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of steroidal compounds used as the host suppressed the quenching, and aromatic hydrocarbons used as the guest were highly deuterated to minimize the nonradiative deactivation of the guest. In the pure organic materials, red-green-blue phosphorescence were realized with a quantum yield >10 % and a lifetime >1 s at RT in air.

Donderdag 12 juli 2012, 16 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door TQC
Onderwerp: Itinerant magnetism in 2D ultracold Fermi atoms with Spin-Orbit coupling: variational approach
Spreker : G. Lombardi, Univ. Padova (Italy)

Abstract: The exploration of Rashba spin-orbit (SO) interaction is stimulated by its increasing interest for spintronic applications.
The first experimental evidences of SO interactions have been found in semiconductor devices. We investigate the behaviour of a 2D ultracold Fermi gas in presence of a Rashba-like spin-orbit coupling.
At ultralow temperatures the fermions interact via contact (repulsive) interactions. We determine the ground state of the system perturbatively up to second order terms in the coupling constant. First we employ the functional integral method that enables us to highlight clearly the similarities with the well known (3D) Stoner model. Then, to overcome some difficulties related to the dimensionality, we analyse the behaviour of the 2D system with a variational approach, both without and with the SO coupling. We focus in particular on the aspects related to the magnetization, and as main result we show how the presence of the Rashba coupling frustrates the emergence of a magnetized phase.

Donderdag 28 juni 2012, 11 u., lokaal U024 (Campus Groenenborger)

Voordracht georganiseerd door TGM
Onderwerp: Phonon Heat Transport in One-Dimensional Quantum-Dot Superlattices and Cross-Section Modulated Nanowires
Spreker: Prof. dr. V.M. Fomin, Institute for Integrative Nanosciences, IFW Dresden, Germany

Abstract: Theory of phonon heat transport is developed for Si-based acoustically mismatched one-dimensional (1D) quantum-dot superlattices [1] and cross-section modulated nanowires [2]. The phonon spectra are calculated in the framework of Face-centered cubic cell and Born – von Karman models of lattice dynamics. The phonon transport is analyzed using the Boltzmann transport equation.
In acoustically-mismatched Si-based 1D quantum-dot superlattices the phonon thermal conductivity can be suppressed by a factor of 5 to 30. The effect is explained by the removal of the high-energy and highvelocity  phonon modes from the heat flux due to their localization in quantum-dot superlattice segments and  the phonon scattering on the interfaces. For instance, in Si/Ge 1D quantum-dot superlattices a strong  reduction of the lattice thermal conductivity down to 0.5 W m-1 K-1 can be achieved depending on quantumdot  sizes and interface quality. These findings are in line with the recently measured values of the thermal conductivity in multilayered quantum-dot arrays [3].
Suppression of the thermal fluxes in the cross-section modulated nanowires as compared to the  homogeneous Si nanowire increases with temperature and reaches the values 1.5 to 5. Increase of the wide cross-section enhances the suppression of the thermal flux due to a rise in the number of the trapped highenergy  phonon modes, which do not carry heat in the cross-section modulated nanowires, and, correspondingly, to a drop in the phonon group velocities in cross-section modulated nanowires compared  with those of a homogeneous nanowire. The obtained results indicate that segmented and cross-section modulated nanowires are promising candidates for thermoelectric and thermoisolation applications.
References
1. D. L. Nika, E. P. Pokatilov, A. A. Balandin, V. M. Fomin, A. Rastelli, O. G. Schmidt, Physical Review B84, 165415 (2011).
2. D. L. Nika, A. I. Cocemasov, C. I. Isacova, A. A. Balandin, V. M. Fomin, O. G. Schmidt, Physical Review B, 85, 205439 (2012).
3. G. Pernot, M. Stoffel, I. Savic, F. Pezzoli, P. Chen, G. Savelli, A. Jacquot, J. Schumann, U. Denker, I. Monch, C. Deneke, O. G. Schmidt, J. M. Rampnoux, S. Wang, M. Plissonnier, A. Rastelli, S. Dilhaire, and N. Mingo, Nature Materials 9, 491 (2010).

Vrijdag 22 juni 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Computer simulations used for a search for Sb-Te, Bi-Te and Bi-Se groundstate structures
Spreker: Kirsten Govaerts, EMAT, University of Antwerp

Abstract: It is common now to consider computation as a third branch of science, besides theory and experiment. The purpose of doing modeling and simulation is to gain understanding and insight, and the benefits are that modeling and simulation can be cheaper, quicker, and easier than experimentation alone.  The aim of our work was to find the Sb-Te, Bi-Te and Bi-Se groundstate structures, with ab initio techniques, and to investigate their energetics and electronic properties. These materials have different important applications in thermoelectrics, phase change materials, and as topological insulators. Using an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations, groundstates of Sb-Te, Bi-Te and Bi-Se can be found without making the dataset of ab initio calculated structures unreasonably large. In order to get a fast convergence we used a (pseudo)ternary cluster expansion, which takes into account the formation of Sb or Bi bilayers after relaxation due to a Peierls distortion of the lattice. The first-principles electronic structure calculations are done within the Density Functional Theory (DFT)-formalism and we explicitly took into account the van der Waals forces, known to be important in these structures.

Donderdag 21 juni 2012, 14 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door TGM
Onderwerp: The gamma-alpha phase transition in cerium as a hidden structural phase transformation
Spreker: Prof. Dr. A.V. Nikolaev, Institute of Physical Chemistry of RAS, 117915, Moscow, Russia

Abstract: Usually different crystallographic forms of a same element are distinguished by their crystal space symmetry. In some cases, for example in metallic cerium, there are two well defined thermodynamic phases: gamma and alpha, which apparently have the same face centered cubic lattice. The existence of such twin phases in cerium has become a challenge to the theory and prompted search of a main factor responsible for the difference. In the talk on the basis of theoretical and experimental studies it is advocated that the well known gamma-to-alpha phase transition in cerium is not really isostructural. This finding makes cerium the first element where the symmetry change is driven exclusively by the valence electron degrees of freedom while the atomic centers of mass (cerium nuclei) occupy the face centered cubic positions.
References:
[1] G. Elisashberg and H. Capellmann, JETP 67, 125 (1998).
[2] A.V. Nikolaev and K.H. Michel, Eur. Phys. J. B 9, 619-634 (1999).
[3] A.V. Nikolaev and K.H. Michel, Phys. Rev. B 66, 054103 (2002).
[4] A.V. Tsvyashenko et al., JETP 111, 627 (2010).
[5] A.V. Tsvyashenko et al., Phys. Rev. B 82, 092102 (2010).
[6] M. Krisch et al., PNAS 108, 9342 (2011)

Vrijdag 15 juni 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Advanced TEM investigation of the plasticity mechanisms in Aluminum nanocrystalline thin films
Spreker: Hosni Idrissi, EMAT, University of Antwerp

Abstract: Nanocrystalline (nc) thin metallic films receive actually special attention from the scientific community because of their use in a variety of technologies ranging from flexible electronics, MEMS, microelectronics, and thin functional coatings. However, the use of these films is still limited by their mechanical properties (the weak ductility and the related strain hardening capacity). Understanding the origin of such feature constitutes a real challenge because: i) The plastic deformation of nc metallic films is very complex and usually involve the simultaneous activation of different elementary mechanisms (dislocation activity, grain boundaries mediated processes, shear band, twinning, etc). ii) Due to the small grain size (below 100 nm) as well as the resolution limit that long persisted in standard transmission electron microscopy (TEM) , the characterisation of the fundamental mechanisms controlling the plastic deformation of nc films at the atomic scale is very difficult.
The aim of the present work is to use panoply of conventional and advanced TEM techniques (HRTEM and HRSTEM including aberration corrected microscopy, ACOM-TEM, in-situ TEM nano-mechanical testing, diffraction contrast electron tomography, etc)  to uncover the fundamental properties of structural defects involved in the plastic deformation of nc Al thin films. This constitutes the key for the improvement of the mechanical behavior and the reliability of these films. 

Donderdag 14 juni 2012, 11 u., lokaal U.244 (Campus Groenenborger)

Voordracht georganiseerd door TGM
Onderwerp: Functional  Oxides: From Multiferroic to Fluxonic Concepts
Spreker: Prof. dr. Roger Wördenweber, Peter Grünberg Institut (PGI-8), Forschungszentrum Jülich (FZJ), Germany

Vrijdag 8 juni 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : The influence of coating of silicon nanoparticles on the electrolyte decomposition in Li-ion batteries
Spreker : Kristof Van Havenbergh, EMAT, University of Antwerp

Abstract: Largely based on its much higher rechargeable capacity compared to graphite, silicon nanopowder appears as an ideal candidate for the next generation of negative electrodes for Li-ion batteries. However, a crucial problem with silicon is the large volume expansion undergone upon alloying with lithium, which results in stability problems. Means to avoid such problems are mostly linked to the understanding of the interfacial chemistry during charging/discharging. In this work, the influence of a coating on the surface of silicon particles on the electrolyte decomposition is examined. Silicon nanopowders with different coating are systematically characterised using transmission electron microscopy, before and after battery usage. Simultaneously, the materials are examined using electrochemical impedance spectroscopy. The aim is to couple both techniques into one powerful screening tool for future battery materials.
In this talk, a brief introduction to battery chemistry will be presented. Then, the first results and encountered obstacles will be discussed. Finally, the future objectives will be shown.

Woensdag 6 juni 2012, 16 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door WN en TQC
Onderwerp: Propagation of single-excitation quantum states through spin chains and James-Cummings-Hubbard arrays
Spreker : Prof. Dr. Ranabir Chakrabarti, Department of Theoretical Physics, University of Madras

Abstract:  It is intended to discuss the time-dependent correlation function describing the evolution of a single excitation state on a linear spin chain with isotropic nearest-neighbor XY coupling, where the Hamiltonian is related to the Jacobi matrix of a set of orthogonal polynomials. For instance, in the case of Krawtchouk polynomial, an arbitrary element of the correlation function can be calculated in closed form showing exact transmission of the state at pre-prescribed time. A similar problem is studied in the context of an one-dimensional array of the James-Cummings-Hubbard system of arbitrary number of coupled cavities, each containing a two-level atom that interacts with a field mode.
References:
1) R. Chakrabarti and J. Van der Jeugt, J. Phys. A 43, 085302 (2010)
2) R. Chakrabarti and G. Sreekumari, J. Phys. B 44, 115505 (2011)

Vrijdag 1 juni 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Molecular imaging meets imaging molecules
Spreker: Dimitri Roose, EMAT, University of Antwerp

Abstract: Contrast particles are used for contrast enhancement in magnetic resonance imaging, especially for in vivo cellular imaging where cells are loaded with these particles. For applications such as the follow-up of stem cell migration, these contrast particles have to reside for long times in the cell. Therefore, the interaction between the cell and the particles becomes important. Toxicity studies have been performed to investigate the cellular response on the presence of these particles, but this interaction has not yet been studied at the electron microscopic level.
In this lecture, an overview of molecular imaging will be presented with a focus on in vivo cellular imaging and the particle studied so far. Afterwards the developed protocol to prepare the samples will be shown, to end with the results achieved this far.

Vrijdag 25 mei 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Determination of 3D growth facets of nanoparticle catalyst for the growth of carbon nanotube
Spreker: Zhanbing He, EMAT, University of Antwerp

Abstract: The physical/chemical properties, especially catalytic properties of nanoparticles are closely related with their enclosed facets, and therefore inspecting facet indexes of nanoparticles has attracted great interest. However, the experimental determination of the growth facets of nanoparticle catalysts in three dimentional (3D) space is very limited. Herein we developed a versatile method to determine the 3D growth facets of a Fe nanoparticle catalyst for the growth of carbon nanotubes. By combining electron diffraction patterns, images, and electron tomography from the same nanoparticle, the indexes of the leading edges of the faceted Fe nanoparticle are well determined as ‹110› type. This method can also be used to determine the facets in a 3D space of any faceted materials, even those with twin defects.

Woensdag 16 mei 2012, 15 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  TGM
Onderwerp: Pseudogap in ultracold Fermi gases:comparison with experiments and Quantum Monte Carlo results and insights for the pseudogap phase of cuprates.
Spreker: Andrea Perali, Physics Unit of the School of Pharmacy, University of Camerino, Italy

Abstract: The origin of the pseudogap is widely debated for cuprate superconductors. The main controversy concerns whether superconductivity and the pseudogap phase are competing with each other or are manifestations of the same phenomenon. In the latter case, pairing fluctuations would extend above Tc the effects of the pairing gap present below Tc [1].
A contribution to settle this controversy can be obtained by ultracold trapped Fermi gases, which are free of the structural complications of cuprates and where only pairing fluctuations are present. In these systems, the attractive interaction can be varied by Fano-Feshbach resonances as to amplify pairing fluctuations.
In this context, wave-vector resolved radio frequency spectroscopy data for an ultracold trapped Fermi gas are reported for several couplings at Tc, and analyzed in terms of a pairing-fluctuation theory. This combined analysis shows that the strongly non-Fermi-liquid behavior associated with the pseudogap coexists with a remnant Fermi surface over a wide coupling range, which in turn sets the boundary of the pseudogap phase [2,3,4].
Moreover, the properties of the pseudogap phase obtained within the t-matrix approach are compared with the outcomes of recent Quantum Monte Carlo ab initio simulations [5].
Once the pseudogap physics has been established and characterized in ultracold fermions, we compare the temperature evolution of the spectral intensity obtained within our theory with the one  measured in cuprates by ARPES [6].
References
[1] A. Perali, P. Pieri, G.C. Strinati, and C. Castellani, Phys. Rev. B 66, 024510 (2002).
[2] J.P. Gaebler, J.T. Stewart, T.E. Drake, D.S. Jin, A. Perali, P. Pieri, and G.C. Strinati, Nature Physics 6, 569 (2010).
[3] A. Perali, F. Palestini, P. Pieri, G.C. Strinati, J. T. Stewart, J. P. Gaebler, T. E. Drake, and D. S. Jin, Phys. Rev. Lett. 106, 060402 (2011).
[4] F. Palestini, A. Perali, P. Pieri, and G.C. Strinati, Phys. Rev. B 85, 024517 (2012).
[5] P. Magierski, G. Wlazlowski and A. Bulgac, Phys. Rev. Lett. 107, 145304 (2011).
[6] T. Kondo et al., Nature Physics 7, 21 (2011).

Woensdag 16 mei 2012, 13 u., lokaal N.108 (Campus Drie Eiken)

Voordracht georganiseerd door  TQC
Onderwerp : Spectroscopic study on quantum phonon dynamics in correlated systems
Spreker : Kai Ji, Institute of Theoretical Physics, University of Heidelberg

Abstract: The nano-scaled ferroelectric clusters come into being in paraelectric BaTiO3 when the temperature decreases close to Curie temperature (Tc).  These ultrafast dipole fluctuations have been discerned in the soft x-ray pump-probe speckle spectroscopy recently. In this talk, I will present a theoretical study on the ultrafast relaxation dynamics of polarization clusters by the path integral Monte Carlo approach. It is shown that the time evolution of speckle pattern is related to the relaxation of ferroelectric clusters. The relaxation rate slows down on decreasing temperature towards Tc as a result of the enhanced critical fluctuations. Application of this theoretical approach to some other phonon related spectroscopic issues will also be briefly discussed.

Vrijdag 11 mei 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Describing matter through theory: e--e- interaction, symmetry and chirality from the low to the high loss response
Spreker : Fabiana Da Pieve, EMAT, University of Antwerp

Abstract: In this seminar I will talk about what theory can do for 1) the interpretation of spectra 2) the interpretation of structural properties 3) for providing  experimentalists reference spectra and new ideas coming from prediction. I will first do a short introduction about how the description of electronic, structural and excited state properties properties is tackled by theory. Then I will focus on the high loss and low loss response in absorption, making connections between the use of light and the use of electrons to probe matter. I will talk about the mercury chalcogenide alpha-HgS, a system which constitutes the red pigment in paintings, plays a role in some photochemical cells and is at the basis of some fundamental reactions on earth. I will show how hidden symmetries in the probe-matter interaction (multipoles) and in the material itself (chirality) can be unravelled both at the core edges and the valence region. Possible future investigations in connection with new forms of dichroism and optical activity are discussed from a mixed theoretical-experimental perspective. 

Vrijdag 4 mei 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Density functional theory: Why it matters to *you*, what you *don't* know about its history, and some striking applications
Spreker: R.O. Jones, Forschungszentrum Julich, Germany

Abstract: The density functional (DF) formalism is the basis of most calculations in condensed matter physics and materials science that avoid using adjustable parameters and experimental input. Applications in chemistry have grown dramatically in the past 15 years, and related theories are important in plasma and nuclear physics. Almost all presentations of DF theory assume that the world was created in 1964, but the real story begins long before this. I shall trace the developments (and the reactions to them!) over the last 80 years, and I shall conclude with some recent applications, including studies of the alloys that make DVD-RW and the Blu-Ray Disc optical memories possible.

Vrijdag 27 april 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Microstructure study of the precipitation behaviour in Co38Ni33Al29 ferromagnetic shape memory alloys
Spreker : Jiangbo Lu, EMAT, University of Antwerp

Abstract: Ferromagnetic shape memory alloys have attracted considerable attentions because of their potential applications in industry as sensors and actuators. In this talk, transmission electron microscopy was performed to investigate the microstructures of g ’ L12 precipitates and their surrounding matrix in two kinds of Co38Ni33Al29 ferromagnetic shape memory alloys. The fastest grown sample with the shortest annealing time reveals eutectic lamellar and dendritic shaped phase in a martensite matrix, with a precipitate-austenite-martensite sandwich morphology at the precipitate-matrix interface. The formation of the sandwich morphology can be explained by the strong martensitic start temperature dependency on element composition. The slower grown sample annealed for a longer time, shows extra facetted sheet-like precipitates with a central ‹111›p twin plane in the austenite matrix apart from the eutectic dendritic phase. These facetted precipitates have a specific orientation distribution due to the existence of the twin planes inside the precipitates plus the Kurdjumov-Sachs orientation relationship between precipitates and matrix. Lorentz microscopy was also applied to study the magnetic domain structures of precipitate and matrix.

Dinsdag 24 april 2012, 16 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door  Dirk Van Dyck
Onderwerp: A History of Max Born and Robert Oppenheimer Approximations in Molecular Physics, Solid State Physics and Mathematics
Spreker: Lucas Lathouwers, Prof. Emeritus University of Antwerp, Visiting Prof. FORTH University of Crete and Visiting scholar Harvard University

Abstract: The 1926 paper by Julius Robert Oppenheimer and Max Born is by far the most cited publication in theoretical, molecular and solid state physics. It is remarkable in its physical, chemical and mathematical contents.
The Born-Oppenheimer and adiabatic approximations break down when electronic states are nearly degenerate. The generator coordinate approximation, introduced by Lathouwers and Van Leuven, on the other hand is capable, in spite of the fact that it is based on a single electronic state, to produce good results when potential energy surfaces closely approach each other. This will be illustrated for so-called curve crossing problems and Jahn-Teller situations. Finally, an extension of the aforementioned coupled oscillator system to a linear chain of alternating masses (to simulate lattice dynamics) will be outlined.

Vrijdag 20 april 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT 
Onderwerp: Spectroscopic Imaging of (Solvated) Soft Materials in the Cryo-STEM
Spreker: Matthew Libera, Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey, USA

Abstract: Traditional methods for studying the morphology of soft materials – both synthetic polymers and biological structures - in the transmission electron microscope (TEM) principally rely on differential heavy-element staining (e.g. Os/Ru tetroxide among others) to induce amplitude contrast based on elastic electron scattering.  This imaging approach has had substantial impact on the electron-optical imaging of soft-materials morphology over many decades of practice, but it is increasingly unsuited for the quantitative mapping of composition with the necessary near-nanometer spatial resolution demanded by a broad range of technologically forward-looking applications.  Our work concentrates on an alternate method based on quantitative maps of composition in unstained soft materials using electron energy-loss spectroscopy to study the inelastically scattered electrons.  Soft materials offer rich electronic structure with which to spectroscopically differentiate between specimen components.  Here we use two examples – synthetic polymer nanoparticles and frozen-hydrated tissue – to illustrate some of the problem-solving possibilities afforded by this imaging approach. More generally, we have achieved 1 nm resolution studying interfaces in poly(styrene)-poly(2 vinyl pyridine) homopolymer blends, 5 nm resolution studying epoxy-alumina composite interphases, and 8-15 nm resolution studying hydrated polymers and tissue where cryo-TEM/STEM techniques are needed.  In contrast to traditional imaging of radiation resistant hard materials where the resolution is ultimately limited by the quality of the electron optics, the achievable spatial resolution associated with imaging of unstained soft materials is instead determined by the radiation sensitivity of the specimen.  Improving the so-called dose-constrained resolution thus concentrates on enhanced data acquisition and spectral-analysis techniques rather than on minimizing the spherical aberration of the objective lens needed to image atomic structure in radiation-resistant hard materials.

Vrijdag 13 april 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: The Biomaterial–Bone Interface: Understanding it in 3D with Electron Tomography
Spreker : Kathryn Grandfield, EMAT, University of Antwerp

Abstract: Interfacial relationships between biomaterials and tissues strongly influence the success of implant materials and their long-term functionality. Due to the inhomogeneity of biological tissues at an interface, in particular bone tissue, two-dimensional images often lack detail on the interfacial complexity. Furthermore, the increasing use of nanotechnology in the design and production of biomaterials demands characterization techniques on a similar length scale. Electron tomography can meet these challenges by enabling three-dimensional imaging of biomaterial interfaces.
This talk will present a background on biomaterials designed for bone interfacing applications, and how electron tomography has been used to reveal details at the biomaterial-bone interface.

Donderdag 12 april 2012, 16 u., lokaal N.008 (Campus Drie Eiken) - AFGELAST WEGENS ZIEKTE SPREKER

Voordracht georganiseerd door TQC
Onderwerp:    Condensate fraction in the BCS-BEC crossover: dimensionality, spin-orbit and multi-components
Spreker : Prof.dr. Luca Salasnic (Universita di Padova, Italy)

Abstract: We analyze the condensate fraction of fermionic pairs for a uniform two-component atomic Fermi gas in the crossover from the Bardeen-Cooper-Schrieffer (BCS) state of weakly-interacting Cooper pairs to the Bose-Einstein Condensate (BEC) of molecular dimers. We derive explicit formulas for condensate density and condensate fraction as a function of the chemical potential and the energy gap both in three [1] and two dimensions [2]. We extend these results taking into account the effect of a laser-induced Rashba-like spin-orbit coupling [3]. Finally, we consider the case of three-component atomic Fermi superfluid with U(3) invariant attractive interaction.
[1] L. Salasnich, N. Manini, A. Parola, Phys. Rev. A 72, 023621 (2005).
[2] L. Salasnich, Phys. Rev. A 76, 015601 (2007).
[3] L. Dell'Anna, G. Mazzarella, L. Salasnich, Phys. Rev. A 84, 033633 (2011).
[4] L. Salasnich, Phys. Rev. A 83, 033630 (2011).

Vrijdag 30 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Strain-Driven Oxygen Deficiency in Nanostructured Superconductors
Spreker: Leopoldo Molina, EMAT, University of Antwerp

Abstract: Precipitates in YBCO thin films yield a significant improvement of the magnetic flux pinning properties and a reduced anisotropy of the critical current density in coated conductors. Therefore, controlling precipitates in size and density, but also understanding their associated strain fields is of crucial importance for applications. YBa2Cu3O7-δ; (YBCO) superconducting films containing nanosized BaHfO3 precipitates were prepared by Metal Organic Deposition (MOD). Strain-fields of crystal defects associated with these precipitates were measured quantitatively by High-Angle Annular Dark-Field (HAADF) aberration-corrected Scanning Transmission Electron Microscopy (STEM). Experimental images were evaluated with respect to the strain tensor components by a geometrical phase analysis and a model-based parameter estimation method. EELS spectra provide fingerprints of the oxygen sublattices of YBCO. Changes in the O K-edge electron energy loss near-edge fine structure (ELNES), in particular of the first peak (which originates from the interaction of the O 2p and the partially occupied Cu d orbital), allowed to distinguish superconducting from non-superconducting areas with a sub-nm spatial resolution. The possibilities of the applied techniques for a structure-property correlation will be discussed.

Donderdag 29 maart 2012, 16 u., lokaal U.203 (Campus Groenenborger)

Voordracht georganiseerd door  EDF
Onderwerp: Asymmetries associated with higher twists: Gauge invariance of polarized Drell-Yan, gluonic poles and twist three
Spreker: Dr. I. V. Anikin, Univ. Regensburg, Germany

Abstract: We explore the electromagnetic gauge invariance of the hadron tensor of the Drell-Yan process with one transversely polarized hadron. The special role is played by the contour gauge for gluon fields. The prescription for the gluonic pole in the twist 3 correlator is related to causality property and compared with the prescriptions for exclusive  hard processes. As a result we get the extra contributions, which naively do not have an imaginary phase. The single spin asymmetry for the Drell-Yan process is accordingly enhanced by a factor of two.

Vrijdag 23 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  TGM
Onderwerp: Oxides in Electronics
Spreker: Chris G. Van de Walle, Materials Department, University of California, Santa Barbara

Abstract: Oxides have many applications, ranging from gas sensors to varistors.  They are increasingly being used in electronics and optoelectronics.  Transparent conducting oxides (TCOs) such as ZnO, SnO2, and In2O3, provide metallic conductivity while absorbing little or no visible light; they are essential for devices such as solar cells, light-emitting diodes, and flat-panel displays.  TiO2 has applications in solar cells and (photo)catalysis, and also, along with Al2O3, Ga2O3, SiO2 and MgO, as a dielectric. Controllable p-type doping would in principle allow for optoelectronic devices such as light emitting diodes and detectors. … (klik hier voor de volledige abstract)

Vrijdag 23 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Big-Bang tomography : a new route to atomic resolution tomography
Spreker: D. Van Dyck, EMAT, University of Antwerp

Abstract: Classical tomographic schemes make use of a large series of projections of an object taken at small angular increments. However for atomic resolution tomography this can pose many problems. First it is not straightforward to perform mechanical tilting in an EM with sub-Angstrom precision over a very large angular range. Secondly many real-life objects such as e.g. an amorphous dielectric layer in a microelectronic device have a geometry that does not give this degree of freedom. And thirdly many objects such as proteins are sensitive to radiation damage so that they do not allow sufficient experimental time and dose for a full tomographic reconstruction at high resolution.
Hence there is need for a new tomographic scheme that can is able to deduce 3D information from only one projection, or from 2 projections using stereoscopy.
In this lecture I will present a totally new tomographic scheme that in principle allows to determine not only the position of individual atoms within the plane of observation but also the vertical position with sub Angstrom precision. For reasons of analogy and intuitive understanding we have called it “big-bang tomography”. We have applied it successfully to the study of a two-layer graphene object.

Donderdag 22 maart 2012, 16 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door TQC
Onderwerp: Dynamics and collective behavior in ultracold neutral matter and plasmas
Spreker: Hugo Terças, Instituto Superior Técnico, Lisboa

Abstract: In this talk, I will summarize some of the aspects of three different aspects of cold and ultracold matter: cold atomic traps, Bose-Einstein condensates and ultracold plasmas. I will firstly explain why the long-range forces mediated by light have put the physics of magneto-optical traps (MOTs) again into the stage. Multiple scattering of photons in the trap is responsible for the emergence of a Coulomb-like interaction between the atoms, which is the root for different collective features, namely the emergence of a cut-off frequency  and a roton minimum in the excitation spectrum, dynamical instabilities and normal modes. Secondly, I will discuss the effects of advection in rotating Bose-Einstein condensates, and how it may open the door for a new collective mode, analogous to the Rossby wave, which is a drift acoustic mode ubiquitous in geophysics. The effects of this drift term is added to the dispersion relation of the usual Tkachenko modes. Finally, I will consider the dynamics of expansion of ultracold neutral (Rydberg) plasmas, by deriving a Thomas-Fermi potential for the electrons. I will conclude the presentation by suggesting the theoretical possibility of observing slow-light in ultracold plasmas, an effect resulting from the combined dielectric response of electrons and two-level Rydberg atoms.

Vrijdag 16 maart 2012, 16 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door  Dirk Van Dyck
Onderwerp: About some oddities in applying standard error propagation laws to climatological measurement. - Is an extreme narrow uncertainty band in time series of global temperature trends feasible?
Spreker: Michael Limburg

Abstract: The lecture is about some fundamentals in error treatment theory and its application to historical climatological temperature data which are used to calculate mean global temperature anomaly time series. By using simple practical examples it will be demonstrated that the total achievable uncertainty can not be lower than that what the proved rules of error detection, attribution and propagation allow. This means that it must be at least as great as total mean global temperature anomaly variation of the last 150 years, but very likely much greater, which would make any attribution an illusory task.

Vrijdag 16 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Transmission electron microscopy and inorganic chemistry needs
Spreker: O.I. Lebedev, Laboratoire CRISMAT, CNRS ENSICAEN, Universite Caen Basse Normandie

Abstract: It is impossible to overestimate the role of XRD and neutron powder diffraction (NPD) as reliable and extremely precise techniques for solving complex structures in inorganic chemistry. However, there are more and more examples of complex structures for which XRD and NPD are unable to find an unambiguous structure solution and explain physical properties, and more input from the nanoscale level of the materials structure (possible superstructure, short range order- disorder effects and possible chemical and structural inhomogeneities) are needed. Indeed, TEM is one of the most powerful and reliable techniques to provide this type of information at an atomic level. Moreover, recent advances in aberration-corrected microscopy allow the acquisition of chemical, structural and even electronic information from single atomic columns. Combining conventional, analytical and advance TEM with XRD and NPD is therefore highly effective in completely solving new structures. The use of different methods of electron microscopy for the needs of inorganic chemistry will be discussed for several examples of new complex materials.

Vrijdag 9 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: 3D structure determination of amorphous  objects using electron wave tomography
Spreker: C. Tang, EMAT, University of Antwerp

Abstract: At present it is possible to retrieve the electron wave in a plane of projection of an object. The basic idea of wave tomography is to backpropagate this electron wave through the object. By repeating this over several projection angles the usual “filtered backprojection algorithm” can be replaced by a “filtered backpropagation algorithm”.
It is the ultimate goal of the project to apply these ideas to reconstruct the 3D structure of an amorphous object. In the first phase of this project we analysed the possibility to use a single graphene sheet as support of a small object such as a nanoparticle. Therefore we started from simulations in which a single atom was positioned on top of a graphene sheet and we tried to reconstruct the position of the atom from the knowledge of the exit wave. In a sense the graphene support was “peeled off”. Next, we could study the precision of this reconstruction as a function of the weight of the atom, the resolution and the noise.

Vrijdag 2 maart 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Perovskite-based anion deficient homologous series AnBnO3n-2
Spreker : M. Batuk, EMAT, University of Antwerp.

Abstract: In this presentation, results of our ongoing work on the perovskite-based AnBnO3n-2 homologous series will be demonstrated. We investigate how the structure of the members with n=4-6 depends on the size of the A and B cations by studying the crystal structure of compounds with different chemical composition (A=Pb/Ba/Bi/Sr, B=Fe/Ti/Sn/Sc).
The crystal structure is built from perovskite blocks with a thickness of (n-2) octahedra connected to each other by chains of edge-sharing tetragonal pyramids. From TEM data combined with synchrotron X-ray powder diffraction data we have established that all compounds are orthorhombic at high temperatures and undergo a phase transition upon cooling, forming a complex monoclinic twinned structure. The model implementing the defect structure into the Rietveld refinement is suggested, allowing a next step towards understanding the structure of these compounds.

Vrijdag 24 februari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp : Towards a Probabilistic Model for STEM Bright-Field Image Simulation : Application to Defocus Measurement and Control
Spreker : A. Tejada, Delft Center for Systems and Control, Delft University of Technology.

Abstract: This presentation summarizes our ongoing work towards formalizing a probabilistic model for STEM bright-field image simulation of amorphous materials. The model includes both the "random" behavior of the specimen and the statistics of the electron counting process, and it is currently used to assess the benefits of a new, alternative technique for estimating defocus from STEM bright-field image data called POEM. This technique, also covered in this presentation, requires potentially fewer image data to estimate the defocus than conventional methods and could lead to faster defocus estimation.

Dinsdag 21 februari 2012, 17 u., lokaal N.008 (Campus Drie Eiken)

Voordracht georganiseerd door  TQC
Onderwerp: Immersing Single Atomic Impurities into Quantum Gases
Spreker: prof.dr. Artur Widera , TU Kaiserslautern

Abstract: Neutral atom based quantum systems have seen great advances in preparation, manipulation and detection in recent years. Two complimentary approaches are pursued to study and control quantum phenomena in these systems: Experiments usually either start from single, individually controllable atoms, or they start from large many-body systems such as Bose-Einstein condensates.
I will present our approach to merge the two worlds of single atoms on the one hand and many-body systems on the other hand in order to combine their advantages. We have developed tools to immerse a single or few Cesium atoms into an ultracold Rubidium gas and study their interaction. We have observed cooling of the single atom down to the temperature of the many-body system through ground-state collisions, paving the way for, e.g., impurity physics in quantum gases with controllable interactions.

Donderdag 16 februari 2012, 16 u., lokaal N.108 (Campus Drie Eiken)

Voordracht georganiseerd door TQC
Onderwerp: Quantum phase transition of a low-dimensional weakly interacting Bose gas
Spreker: Luca Fontanesi, Ecole Polytechnique Federale de Lausanne

Abstract: We study the 1D repulsive Bose gas at zero temperature in presence of spatially correlated disorder. In particular, we focus on the quasi-condensate to Bose glass quantum phase transition due to the interplay of interaction and disorder. The Bose gas is described via an extended density-phase Bogoliubov formalism suitable to treat low-dimensional degenerate systems in the regime of weak interaction. By studying the long-range behaviour of the one-body density matrix and the superfluid component of the gas, we draw the mean  field phase diagram on the interaction-disorder plane. We identify two different power-law relations of the phase boundary that can be explained by scaling arguments valid in the white-noise and Thomas-Fermi limits. In addition, we give a criterion to determine the onset of the phase transition by studying the probability distribution of the density in presence of disorder: this criterion links the fragmentation of the density profile to the loss of superfludity. The last part of this talk is a brief introduction about the physics of the 2D Bose gas in presence of disorder. As this is a very challenging problem both from the conceptual and  numerical point of view, this last part sketches the main open problems and some numerical techniques that we adopt to study thermodynamic properties in the two dimensional case.

Donderdag 16 februari 2012, 11 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Atomic and nanocrystal superlattices: the beauty and the science
Spreker: D. Vanmaekelbergh, Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, University of Utrecht.

Abstract: My two main ambitions in science are the control of the structure of an extended system up to the last atom, and a full mapping of the property-structure relationship. Control emerges on two scales: (i) the atomic scale, i.e. control of the atomic composition and structure, for instance in synthesis of 2-D graphene nanostructures or 3-D semiconductor nanocrystals, (ii) a more extended scale, e.g. the nanocrystal scale in a self-assembled superlattice structure. The relationship between the (electronic) properties and the (atomic) structure is measured with UHV cryogenic scanning probe techniques.
In this lecture, I will first present recent progress in the atomic imaging of graphene nanostructures and ribbons, and single colloidal semiconductor quantum dots. Relating this atomic information to the opto-electronic properties should give insight in the chemistry and physics of these systems.  Second, the self-organization of colloidal nanocrystals into (binary) superlattices will be discussed

Vrijdag 10 februari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Characterization of semiconductor devices through electron microscopy
Spreker: Tyché Perkisas, EMAT, University of Antwerp

Abstract: This lecture will be divided into two parts. The first part will give a brief overview of Scanning Confocal Electron Microscopy (SCEM) and its advantages and disadvantages. The second (and main) part of the presentation will consider semiconductor devices, namely the FinFET and parallel trench devices. In the FinFET device the continuity of the high-k HfO2/TiN layer is investigated through HAADF-STEM tomography, while in the parallel trench structure the presence of defects is studied through HAADF-STEM and simulation.

Vrijdag 3 februari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Formation of the crystallographic shear plains in the Pb-based perovskites
Spreker: Batuk Dmitry, EMAT, University of Antwerp

Abstract: In this talk the formation of crystallographic shear (CS) plains in the Pb-Fe-O and Pb-Fe-Ti-O will be considered. It will be demonstrated that not a simple perovskite, but a more complex partially disordered layered intergrowth structure with the composition Pb2Fe2O5 is first formed in the Pb-Fe-O system and then serves as a parent structure for nucleation and growth of the CS planes. Concerning the Pb-Fe-Ti-O system, it will be shown how the substitution of Ti4+ by Fe3+ in the PbTiO3 perovskite provokes the formation of the CS planes, and how those plains evolve upon the increase of the anion deficiency up to the composition “Pb2Fe2O5”

Vrijdag 27 januari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Hierarchically Structured Porous Materials and Low Dimensional Nanomaterials: from Synthesis to Applications
Spreker: Bao-Lian Su, Center for Nanomaterials Chemistry, Laboratory of Inorganic Materials Chemistry, University of Namur (FUNDP), Namur, Belgium

Abstract: This talk will be divided into two parts, one on the advanced hierarchically structured porous materials, their synthesis, structure characterization, formation mechanism and different outstanding properties. The second part concerns a series of new and unprecedented nanostructures. This part of the talk will illustrate the importance and the need of accurate and multitechnical characterization.

Vrijdag 20 januari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  EMAT
Onderwerp : EELS in the Study of Materials
Spreker : Alan Craven, Department of Physics and Astronomy, University of Glasgow, Glasgow, UK

Abstract: The combination of EELS and aberration corrected STEM is a key tool for the study of materials.   In this talk, the application of the NION UltraSTEM at the SuperSTEM Laboratory to two materials systems will be described.   One is an interface reaction in a metal inserted high-k gate stack for advanced MOSFETs.   The other is the structure of defects in bismuth ferrite doped with titanium and neodymium, a room temperature multiferroic.

Vrijdag 13 januari 2012, 11.30 u., lokaal X.009 (Campus Groenenborger)

Voordracht georganiseerd door  EMAT
Onderwerp: A Thorough Structural Study of 150nm CNT Cu Damascene Contacts
Spreker: Xiaoxing Ke, EMAT, University of Antwerp

Abstract: Carbon nanotubes as promising interconnects in integrated circuits have been studied for some years. Now the challenge comes as the process advances into the integration of structure with top and bottom contacts. Therefore subsequent structural and electrical characterization is required in order to realize a real technological breakthrough in this field. Here a simulated interconnect structure with CNTs integrated in contact holes of 150nm, with underlying TiN contact layer and a Cu single damascene top contact, is characterized by TEM. The special structure is prepared by FIB in order to obtain both cross-section sample and plan-view sample. A thorough investigation of the structure from bottom contact to top contact is performed by combination of cross-section sample and plan-view sample. The study of the structure not only confirms the presence and distributions of CNTs in the contact hole, but also reveals the interface of CNTs in contact with metal layers and substrate. Moreover, the presence of CNTs inside top contact layer by using plan-view sample is successfully demonstrated which shows significant learning obtained with electrical measurements of the structure.