Research team

Electron microscopy for materials research (EMAT)

Expertise

Characterization of structural, electronic, optical and magnetic properties of materials by means of first-principles (i.e. quantum-mechanical) electronic structure calculations. Characterization of the effect of defects and impurities in semiconductors and insulators.

True colours of titanium dioxide - coloured titania and their advanced characterisation for use in CO2 reduction and sensing applications 01/01/2021 - 31/12/2024

Abstract

Titanium-dioxide-based materials (titania) are semiconductors with many versatile applications in chemical catalysis, electrochemical sensing, food industry, energy conversion and many more. A considerable part of these applications rely on the electron-hole formation in titania by the absorption of light in the UV range. However, this restricts many practical applications, since sunlight has a limited UV content. Coloured titania, such as grey and black titania, can be formed via thermal, chemical or sonochemical reduction pathways. Although these materials absorb light in the visible range, there is many conflicting data reported about their activity and involved mechanistic pathways. There is also no consensus on the optimal synthesis routes to enhance specific favorable material characteristics. The large heterogeneity in coloured titania materials and their syntheses used in literature hampers a clear correlation between synthesis, electronic structure and activity. In this concerted action, we aim at a controlled alteration of the reduction conditions of porous titania linked to a direct determination of a variety of properties, such as electron traps, surface-adsorbed and surface-reacted species, bulk defects, band gap, polymorphs and pore sizes, and to activity measurements. For the latter we will test their capacity for photocatalytic reduction of CO2 and their applicability as electrode material in the electrochemical sensing of phenolic compounds in water. With this approach we guarantee that the results of the different experiments can be directly compared and correlated. This will allow determining the key factors governing the relation between synthesis, electronic and geometric structure and activity of coloured titania. This knowledge will be translated in optimal synthesis conditions for the here proposed applications, of importance in sustainable chemistry and development. The project makes use of the unique complementary expertise in the synthesis, experimental and theoretical characterization and application of titanium-dioxide-based materials available at UAntwerp.

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Hybrid spin-charge quantum systems based of single point defects in diamond: Combined theoretical and experimental approach. 01/01/2021 - 31/12/2024

Abstract

Individual point defects in diamond crystals belong to an important class of quantum systems denoted as solid-state qubits. Such point defects, as for example NV, SiV, are intensively studied in the field of quantum sensing and metrology but also quantum information science. The applicants recently developed a novel technique, photoelectrically detected spin resonances in diamond, which brings promises for a new category of quantum devices that can be coupled with classical semiconducting electronics. The photoelectric readout is fundamentally based on charge state transitions in single point defects. In this respect, the photoelectric method differs from optical detection in two level quantum systems. In our proposal we would like to use this basic property of photoelectric readout and realise a novel type of qubit - charge-state solid qubit - using the transition between the different charge state of the same defect. Combining with the spin manipulations a hybrid quantum systems can be conceived. The proposal is based on preliminary results demonstrating the SiV charge state readout. To devise the mechanism of charge state transitions we will use predictive ab initio calculations theoretical methodology, permitting to determine the energy position of charge state levels in the diamond gap, photoionisation cross section, rates and the electron transport coherence with respect to the driving field. We will demonstrate charge-qubit superposition and two qubit entanglement.

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Computational modeling of materials: from atomistic properties to new functionalities. 01/01/2019 - 31/12/2023

Abstract

Computational modeling is an essential factor in the study of the properties of materials. Nowadays, computational modeling is extensively used to predict and develop new materials. This requires a thorough knowledge of the local atomic (structural and electronic) structure and its influence on the macroscopic properties. Although, in principle, all materials can be described with the laws of quantum mechanics, it is impossible in practice to derive all material properties from these. Even with today's most powerful supercomputers, quantum mechanical electronic structure calculations are limited to a thousand atoms and to a maximum of 1 ns. To study length and time scales that go beyond these atomic scales, (semi-) empirical techniques are used and further developed through multiscale modeling. Transitions between models describing at different time and length scales are achieved by studying the relevant scale with the appropriate computational techniques. In order to have a thorough understanding of materials properties it is therefore important for collaborations between computational groups with expertise on different methods to flourish.

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Spent Fuel – Corrosion Modelling 01/10/2018 - 30/09/2023

Abstract

In this project we provide an atomistic description by means of quantum mechanical density functional theory calculations of the defects that occur during the corrosion of UO2 to U3O8. In particular we investigate the properties of the intermediate oxide U3O7, which is the main precursor to the formation of U3O8. We investigate the influence of external factors like water and grain boundaries on the oxidation of UO2. The formation mechanisms of U3O8 are essential to understand the degradation of spent fuel under storage conditions.

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Improving the performance of rock salt type cathodes for Li-ion batteries through control of the transition metal cation migration using redox reactions of the oxygen sublattice and Li-conductive coatings. 01/01/2016 - 31/12/2019

Abstract

The performance of Li-ion batteries is still far below the threshold for automotive and grid applications. This largely depends on the cathode. The commercially most developed cathode is LiCoO2, but there is a better alternative in LiNixMnxCo1-2xO2(NMC). However, even the best NMC still suffers poor electrode kinetics and large voltage decays on cycling, due to structural rearrangements upon charge-discharge. We propose to engineer the reversibility of the structural transformation also in NMC by coupling the TM cation migration with redox changes at the oxygen sublattice through dedicated TM cation replacement. We also propose to develop a Li-ion conducting coating to prevent contact between electrolyte and cathode to stop oxygen and cation loss and improve the capacity retention.

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Functionalisation of nanostructured semiconductor metal oxides for chemical sensing (FONSENS). 01/10/2015 - 30/09/2018

Abstract

The objective of FONSENS is to develop breakthrough technologies in gas sensing that will provide higher sensitivity and superior selectivity at reduced cost and power consumption. This objective will be pursued by integrating complementary skills of EU and Russian groups. The main strategy in FONSENS for achieving enhanced sensor performances is to develop new nanostructured materials, which will allow control of concentration of active centers over a broad range for selective detection of toxic gases of different nature. The development of new generation of gas sensing materials will be supported by computational modeling with ab initio DFT calculations and a wide range of high resolution morphological and physico-chemical characterization techniques including (scanning) transmission electron microscopy and electron diffraction.

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Determining the concentrations of cargo vapours around a ship's superstructure by wind tunnel experiments and CFD. 01/01/2015 - 31/12/2016

Abstract

This project will quantify the concentration of cargo vapours around the ship's accommodation and investigate how to improve the situation. Wind tunnel experiments and CFD calculations will in addition to the existing on‐board measurements help to visualise the streamlines around the accommodation. Based on these results we will draw up guidelines to the crew on how to minimize cargo vapour concentrations around the superstructure in relation to the different cargo handling operations

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Project website

Quantification of target surfaces (QUOTAS). 01/01/2014 - 31/12/2017

Abstract

The overall objective of the research proposal is to elucidate the chemical composition of the target surface under different experimental conditions, and using this chemical information to calculate the electron yield by first-principles techniques and the sputter yield by Monte Carlo techniques. In this way, the project combines experiments and calculations to obtain quantitative data about two fundamental processes during reactive magnetron sputtering.

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A first-principles study of grain boundaries in CIGS absorber layers. 01/01/2013 - 31/12/2016

Abstract

Grain boundaries in polycrystalline materials are known to play a critical role in determining their electronic properties. For several reasons, polycrystalline materials are at the heart of many present day electronic devices. Thus, a thorough understanding of the physics of grain boundaries is of fundamental importance for the design of devices with increased efficiency. The problem is compounded by the fact that the typical presence of nonnegligible concentrations of impurities and defects leads to a phenomenology that can be very different from that occurring in the bulk. In this project we will consider as a case study the chalcopyrite CuIn1-xGaxSe2 (CIGS) systems, which are of great current interest. Indeed, although today photovoltaic cells are still largely built with Si-based absorber layers, the low absorption coefficient of Si has prompted research on cells based on thin-film absorber layers, with higher power-to-weight ratios.

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BOF: 1 year doctoral fellowship (Kirsten Govaerts). 01/01/2011 - 31/12/2011

Abstract

This project represents a research contract awarded by the University of Antwerp. The supervisor provides the Antwerp University research mentioned in the title of the project under the conditions stipulated by the university.

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Computational modeling of materials. 01/01/2009 - 31/12/2013

Abstract

The goal of this Scientific Research Community (Wetenschappelijke Onderzoeksgemeenschap, WOG) of the FWO-Vlaanderen is to intensify the collaboration between the different research groups in Flanders which are active in the field of the computational modeling of materials. In addition a collaboration with the external partners will be set up or intensified.

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XANES meets ELNES: a study of heterogeneous materials at different length scales. 01/01/2009 - 31/12/2012

Abstract

The project aims to confront and compare the results of two related techniques for obtaining information on the structural environment of metals in solid materials: X-ray absorption near-edge spectroscopy (XANES) and electron loss near-edge spectroscopy (ELNES). Both probe the density of unoccupied electron states in atoms and the manner in which this distribution is influenced by the neighbours of these atoms. Both methods employ different primary projectiles (resp photons and electrons) and different ways modes of detection; as a result they operate on different length scales.

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In Silico Materials Design and experimental validation for novel optical coatings (ISIMADE). 01/01/2009 - 31/12/2012

Abstract

The primary objective of this SBO is to develop advanced tools for pragmatic materials modeling. However, to stimulate the interaction with experimental work at Flamac and their industrial partners early on, we have targeted one application area; particularly optical thin film materials. These applications have been chosen on the basis of their high technological relevance, industrial interest in Flanders, environmental issues, and feasibility to make impact with modeling.

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Electronic and optical properties of transparent conducting oxides: an ab initio study. 01/01/2008 - 31/12/2011

Abstract

Within this project we will study in a systematic way the relation between composition and structure versus the electronic and optical properties of transparent conducting oxides (TCO) by means of ab initio electronic structure calculations.

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Phase stability of Ge-Sb-Te alloys : an ab initio study. 01/07/2007 - 31/12/2011

Abstract

The phase stability of Ge-Sb-Te alloys is investigated as a function of composition and temperature by means of ab initio electronic structure calculations, cluster expansions and data mining techniques. The presence of vacancies on the Ge/Sb sublattice is fully taken into account and for the ground state structures the optical properties are investigated through a calculation of the dielectric function.

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Quantitative analysis of electron energy loss spectroscopy of nanostructures. 01/10/2005 - 30/09/2007

Abstract

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FWO Visiting Postdoctoral Fellowship. (Antonina KRAVTSOVA) 01/10/2005 - 30/09/2006

Abstract

The local (electronic) structure of perovskite-based interfaces will be investigated computationally by means of ab initio electronic bandstructure calculations and the Multiple Scattering technique. In particular the finestructure of the electron energy loss spectrum will be calculated and interpreted in terms of the local (electronic) structure of the interface.

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    Measurement and computation of accurate electron scattering data for composition analysis in ternary semiconductor nanostructures. 01/01/2005 - 31/12/2008

    Abstract

    The aim of the suggested research project is the computation and measurement of electron scattering data in ternary semiconductors, needed for accurate compositional analysis of semiconductor nanostructures such as In(x)Ga(1-x)As quantum wells and quantum dots by high resolution transmission electron microscopy. The planned research project is a collaboration between an experimental group (EMA T, Electronenmicroscopie voor Materiaalonderzoek) and a theory group (TSM, Theoretical Study of Matter) of the University of Antwerp. The goal of the project is twofold. First, structure amplitudes, Debye-Waller factors and static displacement effects will be computed theoretically for technologically interesting materials such as e.g. InGaAs, AIGaAs, GaAsSb, CdZnSe and CdZnS. Second, intensities of diffracted beams will be measured in these materials and compared with our theoretical data. In this way, we aim at providing more reliable data for structure amplitudes and Debye-Waller factors. Our research will improve the accuracy of composition determination in ternary semiconductor nanostructures, and will provide accurate data for any quantitative transmission electron microscopy investigation of these materials. Furthermore, methods developed for theoretical calculation of structure amplitudes and Debye-Waller factors will be applicable to almost any type of material. Therefore, this work will make a substantial contribution to improved quantitative analysis of transmission electron micrographs in general.

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    Network for Actinides Sciences (ACTINET-6). 01/03/2004 - 29/02/2008

    Abstract

    The goal of the network is to revitalize actinide research and to ensure the highest level of expertise in Europe through the dissemination of knowledge and the organization of education and training activities. The research activities of the participating partners will be brought together and a strong collaboration between the laboratories will be organized e.g. through the exchange of scientists. The network aims at making nuclear research more attractive to young scientists.

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    Ab initio calculation of EELS and XAS spectra of actinide oxides. 01/10/2003 - 31/12/2005

    Abstract

    Calculation of EELS and XAS spectra of actinide oxides e.g. U02, PU02, Am203 by means of ab initio electronic structure calculations. The calculations are performed with the LAPW method within the DFT methodology. In order to get an accurate description of the strong correlation of the 5f electrons we consider both the LDA and the LDA+U approximation for the Exchange-Correlation functional.

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      Ab initio calculation of mean inner potentials and Debye-Waller factors for technological important semiconductors. 01/10/2003 - 30/09/2004

      Abstract

      For quantitative electron holography it is essential to know the mean inner potential V0, which describes the phase shift of an electron wave transmitted through a crystalline specimen of thickness t with respect to a reference wave going propagating in vacuum. With an accurate knowledge of the mean inner potential one can precisely determine the specimen thickness. We perform first-principles calculations within the density functional theory formalism to determine the mean inner potential of II-VI semiconductors (e.g. ZnSe, CdSe, ZnS, CdS, ZnO, CdO). In addition we calculate the Debye-Waller factor of those materials, which are needed for quantitative determination of the composition of sphalerite type semiconductor heterostructures by the CELFA method. CELFA compares the local (002) Fourier coefficients of transmission electron microscopy images with (002) Fourier coefficients calculated by Bloch-wave simulations. The local (002) Fourier coefficients strongly depend on the local composition of the heterostructure. The accurate knowledge of the Debye Waller factors of the semiconductors is needed as an input parameter for the Bloch-wave simulations, because the accuracy of the measured composition is directly effected by the accuracy of the Debye-Waller factors used as input.

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        01/10/2003 - 31/12/2003

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          Dynamics of fullerene molecules in C-nanotubes (peapods). 01/01/2003 - 31/12/2004

          Abstract

          The dynamics of C60 (and C70) molecules encapsulated in single-wall nanotubes, (C60)n@SWNT, will be studied by analytical and numerical theory. Molecular and site symmetry adapted rotator functions will be constructed. A model for the intermolecular potential and the molecule'wall potential will be established. Orientational density distribution functions and correlation functions will be studied. The possibility of orientational and structural phase transitions will be investigated. Raman and NMR experiments will be explained.

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            01/03/2002 - 31/03/2005

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              Quantum Chemistry : fundamental and applied aspects of Density Functional Theory. 01/01/2002 - 31/12/2011

              Abstract

              This Scientific Research Network of the FWO-Vlaanderen brings brings together several research groups active in the field of Density Functional Theory.

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              Theoretical study of dynamical, thermal and optical properties of carbon nanotubes. 01/10/2001 - 30/09/2002

              Abstract

              The dynamical, thermal and optical properties of carbon nanotubes will be studied computationally within empirical, semi-empirical and ab-initio approaches. In particular, the phonons, elastic moduli, heat capacity, absorption, and Raman spectra will be calculated.

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                RAFO financial support for the 1-day symposium "Many electron theory for molecules, clusters and condensed matter" in the framework of the Francqui chair of N. March, 12.10.2001, Antwerpen. 01/10/2001 - 31/12/2001

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                  Computational design of molecules and materials. 01/01/2001 - 31/12/2004

                  Abstract

                  It is the purpose of this project to unify a number of theoretical methods and techniques from different fields (quantum chemistry, condensed matter physics and statistical physics) related to molecules and materials into a coherent software package allowing to tackle a wide variety of problems of interest to the industry.

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                    Thermo-elastic properties of amorphous polymers. 01/01/2001 - 31/12/2002

                    Abstract

                    Study of the thermoelastic behaviour of amorphous polymers (polyglycine and nylons) by using Molecular Dynamics and Monte Carlo simulations. The atomistic calculations are based on empirical interatomic interaction potentials. The elastic constants (and moduli e.g. Young's modulus) are derived from the strain-strain fluctuations within the Parrinello-Rahman approach. The effect of temperature, pressure and additives on the elastic behaviour of the polymers is also investigated.

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                      Ab-initio molecular dynamics simulations of MgSiO3, 01/05/1999 - 30/04/2001

                      Abstract

                      In this project the structural, elastic and electronic properties of MgSiO3 will be investigated by means of ab-initio density functional theory. This will be done in collaboration with foreign groups.

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                        Ferroelectrics and dipolar glassesì 01/10/1990 - 30/09/1992

                        Abstract

                        Microscopic study of ferroelectricity and structural phase transitions in mixed crystals. Phase transitions in nitrites and perovskites. Dielectric properties. Influence of substitutional disorder on various properties.

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